Amending Soils—Why??

I think the blog and garden professors web page is pretty full of research and benefit descriptions of mulching, particularly with arborist chips. A little less clear is the role of amendments in garden soils. I always like to ask the “why” questions for gardening practices. Like “why” prune trees? Why fertilize, etc? Ideally gardening practices should be founded on a basis of science and inquiry as to their necessity. Poor structure early structural training or a damaged canopy may prompt tree pruning, mineral nutrient deficiency symptoms may suggest

When amending, organic materials are often tilled in 50% by volume (3 inch layer tilled six inches deep)

fertilization. So why amend your garden soil? For me as a gardener you do this because your soil is not providing something you think your garden or plants growing in that soil need. This could be nutrients, or water. Amending as a soil or garden practice is best done in garden beds that host annual plants: vegetable gardens, color beds with annual plants etc. Obviously we are not going to lift all the perennials just to add some amendment under their root systems. We can also make arguments that amending soils that you are going to plant perennials in is unlikely to be helpful. So why amend?

 

Research on providing amendments in the holes of perennial plants has most often shown no significant differences compared to plants installed with just native backfill. There are lots of reasons for this and I can imagine some soils where amendments would give a slight boost, but these were not the soils most studies used (extreme sands). Mostly, perennial roots do not reside in the planting hole for long, so the time that amendments would be effective is very short. Since amending can also harm some plants if done incorrectly, University of California does not recommend the practice, neither did Harris for trees, shrubs and vines. Nor did we find any effect in palms (Hodel and others). For this blog we will assume that amending is restricted to annual plant beds. So why amend? The usual reason I hear is: “My soil is crap!” I think it would be interesting to survey people about their soil and see what they think about it as compared to how it actually grows. Most people seem to disparage their poor soil….So many gardeners believe that if they add something to their crap soil it will get better. Maybe, or no. Amending has potential benefits and detriments depending on what and how much you amend with.

snaps growing in soil amended with high quality yardwaste compost
Snaps growing in soil with uncomposted yardwaste used as an amendment. Nitrogen is immobilized

So the potential benefits of amending are:
• rapid (immediate) modification of the planting bed
• potential increase of moisture holding capacity in the soil
• potential increase of nutrients and nutrient holding capacity (cation exchange capacity of the soil
• change in the soil texture, porosity
• rapid increase in soil organic matter
• suppression of soil borne pathogens

Potential detriments include:
• nutrient draw from the soil (nitrogen immobilization: see images above)
• toxicity from residual phytochemicals
• adding pests (weeds or root pathogens)
• soil structure is destroyed
• soil food web is challenged and harmed
• may increase soil salinity
• contaminants can be transferred to gardens

One of the incontrovertible facts about amending is that you have to disturb the soil to do it. Amending involves digging in, roto-tilling, soil turning with a spade, or some kind of incorporation process. Usually the more the better. This destroys soil structure and a good part of the soil food web. Beneficial nematodes are highly sensitive to tillage and many are killed by tillage, often perturbing the entire soil food web in a disturbed soil (See research by Howard Ferris). The beauty of mulching is that the soil structure is not initially influenced only assisted in its further development. The downside is that mulches take months or years to have their effect. While amending can give immediate physical, chemical and biological assistance to soil, it also may bring pathogens, salts, toxic phytochemicals or weeds to your garden depending on what you choose to use as an amendment. Soil tends to be very resilient, so structure destroyed by amending is usually back in place at the end of the cropping cycle in many cases. The need for further amending should be considered carefully after each rotation.

So you still want to amend? What do you amend with? In the case of mulching we (Garden Professors) make a strong argument for freshly prepared (not composted) arborist chips. Nothing could be worse for amending (at least in the short term). Un-decomposed substrates such as wood chips are high in carbon and low in nitrogen. They will cause the microbial community of soil to attack the carbon and utilize all the free nitrogen in the soil, screened or fine materials after composting have greater surface area and will enhance the water absorbing and nutrient holding properties they give to soil. Furthermore, well composted substrates or feedstocks will be free of pathogens and other pests so they should be “safe” for your garden. Composts that are made from plant feedstocks tend have concentrations of plant required minerals. Since composts lose about 2/3 of their carbon and moisture during the decomposition process they have a much higher mineral content than their feedstock. Manures have already been partially composted by the animals that made them. Additional composting increases their salt levels sometimes to plant damaging levels. Manures should be used with care, or in lower quantities as they can damage sensitive plants. Some manures and composts can be contaminated, since some long term soil-residual herbicides such as clopyralid are not broken down in the composting or animal eating process.

soil amended with peat moss
Soil amended with composted coffee grounds

Gardeners are inventive in their use of compost and amendments, so there are many ways to amend soil. Peat moss has been the gold standard amendment for many gardens. However due to environmental damage, sustainability of peat moss use is questionable. Coco fiber or coir is a good amendment, but it can bring high salts with it depending on how it was processed. Biosolids are phenomenal amendments and often produce growth responses, but there can be issues with metals and other biological contaminants in biosolids. Home-made compost is a good amendment because you know what is in your compost, as long as it is properly prepared and cured, it can function very well. Greenwaste or yardwaste compost is a possibility, but from my experience, most of these if commercially produced are not well prepared, and are not mature (they still heat up if piled). Many gardeners like coffee grounds, and with the advent of large coffee companies, grounds may be available in bulk quantities. Be careful though as some sources of coffee are toxic to many plants and their use should be limited in any amending situation.

What about rate? In my research I have always tried to amend soils 50% by volume. So a three inch layer of amendment tilled six inches deep has been my goal. Most annual plants have their roots in the upper six inches and this strategy works well. Also, most rototillers are only good for about a six inch depth. If you intend to dig deep with a spade and incorporate to depths beyond six inches, increase the amounts accordingly.

What kind of soil needs amending? Another way to view this is, “have you tried growing without amending? Many soils grow very well with just added nutrients. Typically sands will most benefit from added amendment due to increased water and nutrient holding capacity. I also like to amend clays because they become easier to plant in over time, however the initial go round may be difficult. Clays are very nutritive so amendments may make you feel better gardening in them, but often plants grow very well without amending clay soils. Plant responses to amendments are best in sands.

How often should I amend? This is up to you, but organic matter is “burned up” by the soil microbial community rapidly because 1) you are tilling and this accelerates microbial activity; and 2) you are likely amending during the growing season when warm soil temperatures favor organic matter breakdown. Most gardeners amend after replanting the bed.

References

Ferris, H., and M.M. Matute. 2003. Structural and functional succession in the nematode fauna of a soil food web. Applied Soil Ecology 23:93-110

Harris, R.W. Arboriculture: Integrated management of landscape trees, shrubs and vines. 1992. Ed. 2 Prentice-Hall International, New Jersey. 674pp.

Hodel, D.R., Downer, A.J., Pittenger, D.R. and P.J. Beaudoin. 2006. The effect of amended backfill soils when planting five species of palms. HortTechnology 16:457-460.

Plant Control to Major Tom(ato): The Art of Spacing Out Your Plants

“Why don’t you just plant it up against the house,” piped my mother-in-law.  She was talking about a run-of-the-mill “old fashioned lilac” that we had received in the mail for our donation to Arbor Day.  While I don’t necessarily think of the organized tn as a source of high-quality or novel plants, I felt beholden to  make a donation since it was founded and is still located in Nebraska (and we have visited the Arbor Lodge, home to founder J. Sterling Morton and his brood of tycoons (one of salt fame – that Morton, one of cornstarch fame – ergo we have Argo, and one of the railroad).  I had pawned the 10 blue spruce off to the freebie table at the office, but she wanted a lilac…and what momma-in-law wants, momma-in-law gets.

I explained to her that the labeled final size of the cultivar was 12 feet in diameter, so it needed to be at least 6 feet from the house (preferably more) and from other plants.  “Nonsense!” she decried, “I planted mine close to the house.  You just have to keep it pruned back.  Mine did just fine….. until it rotted.”  Since the right spacing would put the shrub in the middle of a narrow passage between the house and the fence, I opted to throw it into a pot since I was heading out of the country the next day for two weeks.  It was, after all, a little more than a spindly twig (with roots wrapped together in a ball) sheathed in plastic.

What’s the issue? 

Most gardener’s desire for instant gratification often means that correct spacing for the finished size of the plant gets thrown out the window so that the garden looks good to go from the beginning.  Or even worse, plants get shoved against houses, under power lines, or in other areas where they’ll either be cramped and crowded or incessantly pruned to the point of oblivion throughout their probably shorter-than-expected lifespan.  Think of it like your bubble of personal space.  Just like you don’t want to be crowded, neither do plants.

In addition to the pruning and space issues, crowding can increase the likelihood of disease or other plant issues.  Crowded plants reduce air flow, which aids the development of diseases by increasing (ever so slightly) the humidity in the plant’s microclimate, increasing drying times after rain or irrigation, and even allowing for disease spores to more easily settle on the plants.  For perennials, and especially trees and shrubs, overcrowding can be a chronic issue since the problem can last for many, many years.

That’s not to say that spacing it isn’t a problem with annuals, either, especially in the vegetable garden.  In addition to the increased possibility of disease, competition for space and for nutrients can reduce yields.  Crowded root crops like carrots, beets, and radishes don’t have enough space to fill out, resulting in stunted and irregular produce. The same goes for leafy crops like lettuce or kale.  Fruiting crops like tomatoes and peppers can also suffer from reduced production when plants can’t fully grow to their potential.

Getting Spacing Right: The Simple Art of Not Planting Too Damn Close

Perhaps the secret is complicated formula for figuring out the proper plant spacing?  Or perhaps it is some specific planetary alignment you need to wait for?  Since it seems to mystify may gardeners, spacing must be difficult, right?  Au contrare!

Most plants come with the proper space printed right on the label!  Think of such a novelty!  That lilac my MIL wanted to plant against the house said right on the packaging that it generally grew to 12’ wide.  If I were planting a bunch of them in a row (and not as a hedge), I could plant them 12’ apart.  If I wanted to grow them as a hedge, I’d reduce that spacing to make them grow into each other (but it will take time for them to grow into a hedge…so they won’t be touching right away).  Keep in mind that this is the genetic potential of the plant and isn’t a guarantee.  Many factors, including microclimate, soil conditions, precipitation, nutrient availability, disease, etc. etc. etc. could limit the plant’s growth to that potential (or even more rarely increase it).  What if I’m not planting a bunch in a row?  Here’s were a teensy bit of math comes into play.

Think of plants in general terms as circles.  Just look at a basic landscape architect’s plans and you’ll sometimes see plants represented generally as circles.  If you think all the way back to that geometry class in high school, you’ll remember that there are several measures of a circle, including the diameter and the radius.  The diameter is the width of the circle from one side to the other. The radius is the distance from the center point of the circle to the edge.  So if our plant is a circle, then the listed width of the plant is the diameter and the distance from the trunk, stem, or center is the radius.  So I can expect my lilac (if it reaches full potential) to grow out 6 feet from the trunk.  That means I need to plant it at least 6 feet away from the wall.  If I wanted to plant it in the landscape with other plants around it, I would need to figure out the radius of the plants I wanted to plant close to it and add their radius to the lilac radius to figure the minimum distance I should plant them apart.  Let’s say I wanted to plant a small shrub beside the lilac with listed width of 10 feet.  That means the radius of that shrub is 5 feet.  Adding them together, I get a distance of 11 feet.  On the other side of the lilac I want to plant a large perennial with a diameter of 4 feet.  The radius would be 2 feet, so my minimum planting distance would be 8 feet.  You also have to keep in mind any variation due to microclimate and environmental factors.

What about the vegetable garden?

The same concept holds true for the vegetable garden as well – think of each of the plants as a circle.  Where planning the spacing is different is usually interpreting what the seed packet says in terms of in-row versus between-row spacing.  The in-row spacing is based on the size of the plant, a general idea of the size of the circle the plant makes or how much space it needs between plants (some plants, like beans, are OK when they overlap a bit and share space).  The between-row spacing is for human use in creating typical in-ground, large garden areas.  I’ve had the discussion before of large garden area vs. in-ground beds, vs. raised beds so we don’t need to go into that detail, but the general movement is toward some sort of bed system to reduce walkways (reducing bare soil that can lead to erosion or compaction when walked on) and intensify plant spacing/output per a given area.

Taking that into consideration, use the in-row spacing as the between plant spacing in all directions.  This is what the popular Square Foot Gardening method does – the spacings and number of plants per square are based on the between plant spacing and eliminates row spacing.  For example, radishes and carrots typically have an in-row or between plant spacing of 3 inches.  If you fit that spacing evenly within a foot row segment, you get four plants.  When you make that two dimensional you get 16 plants per square foot.  For four inch spacing you get 3 per foot and 9 per square foot, six inch spacing you get two and four, etc.  You can fill an entire bed with plants like this without spacing between rows of plants.

Of course, the tricky thing is that, just like our trees and shrubs that are planted too closely reduced airflow and increased microclimate humidity can increase the risk of diseases in the plants.  The Square Foot Gardening method by the book states that you shouldn’t plant any adjacent square with the same crop to decrease likelihood of disease sharing, but that seems sounder in theory than in practicality. I use some of the spacing (and you don’t need the book, just look at the between plant spacing and calculate. You just have to monitor, use good IPM, and treat or remove issues promptly to reduce disease issues. Using interplanting to intensively plant by mixing various space usages (tall plants with short plants, root crops with fruit crops) can also help make use of the space while mixing plants to reduce disease spread.

Problems with Planting Trees

 

Ok. I admit this blog is going to turn into a rant pretty quick because there seems to be a lot of ways to screw up a fairly simple horticultural practice—tree planting.  Since Arbor days are happening/happened everywhere around now, its a good time to talk about how to plant trees.   First let me state some simple and useful guidelines for a successful tree planting.

-When at all possible, plant trees bare-root. Even washing the container media away. This allows for inspection and removal of root defects.
-Select trees carefully that are free of defect and disease and that are adapted to your climate and soils
-Plant the youngest tree you can
-Take care in choosing the planting site.
-Avoid Root Barriers
-Plant trees so that the root flare is above ground slightly
-Plant trees in a hole only deep enough to contain the root system, no double digging.
-Plant trees in a hole wide enough to contain the root system, no wide holes (unless there is a reason for using one)
-Fill the hole with soil removed to make it. Do not amend the backfill around newly planted trees—Do not put rocks in the bottom of a planting hole!
-Plant trees without staking unless there is a reason to stake them
-Plant trees away from turfgrass or other groundcovers.
-Plant trees under the cover of a fresh layer of arborist chips.

-Irrigate newly planted trees from the surface—Do not install U tubes or tree snorkels to irrigate deeply.

An old planting detail from “a book of trees” . Several myths here: rocks at the bottom of the hole, amended hole, nursery stake still there when it does not need to be, etc.

I guess this rant comes from the variety of tree planting specifications I have seen over the years used by municipalities, landscape architects, nurseries and others. There seems to be a need to use the latest product, method or modification to site soils in order to make a fancy planting detail. Simpler is better and research by Universities has not verified most of the “innovative” approaches seen in planting details.

The first step in planting a tree is to chose the tree you want to plant. While this seems simple there is a lot that goes into tree selection. Setting aside personal choices, it comes down to selecting a tree that is healthy and free of defect. The potential candidate tree should have no signs or symptoms of disease, a naturally developed canopy unfettered by nursery pruning (especially heading cuts), and has few or no root defects. Initial superficial examination of the root collar in the nursery can eliminate some trees with circling or girdling roots. However, when the tree is planted root washing will reveal the entire root system and as Dr. Linda Chalker Scott has shown in this forum, root washing allows for rapid establishment in site soil. When at all possible chose the youngest tree you can for the new site. Young trees have fewer root defects, and we have the advantage of training them (structural pruning) from an early age. Young trees establish rapidly and will often outgrow older, boxed trees. The larger the specimen that you plant, the more chance for establishment problems such as settling, drying out, root rot or just slow growth. Planting trees from seed is ideal but most gardeners don’t have the patience to wait and seedlings, and seedlings do not give the option of using cultivated varieties that impart horticultural value, such as predetermined flower color, disease resistance, and known form (canopy shape and size).

Once the tree is selected, purchased and root washed, it is time for setting it in the ground. The first step is choosing a good planting site. A good site for a tree is somewhere that provides adequate soil volume for its roots to expand and for its canopy to expand. Many trees in urban settings fail to achieve their potential because they have restricted spaces to grow in. Chose a location in full sun. Unless you are planting a species that grows well in shade or needs protection from the environment, most trees will grow best in a sunny location. While trees are forgiving of most soil conditions, they will not grow well in compacted soils. If this is all that is available, break up compacted soils before planting. Consider the ultimate size of the tree you are planting, and imagine it attaining that size in your planting site. Avoid sites that have close proximity to buildings or hardscape. One of the most frequent problems with trees is that as they attain mature size they conflict with the infrastructure at the site.

Dig the hole for your tree so that the roots are very slightly above the grade. Do not double dig! While double digging has its proponents, there is no research-based reason for destroying soil structure– it is a disaster for tree planting. When a hole is dug too deeply soil will always settle after planting and irrigation resulting in the tree being planted too low in the ground. The root collar is buried and this is a predisposing factor for disease. The hole should have undisturbed soil under the roots. The hole only needs to be as wide as the root system. While many planting details show wide holes these are not necessary in most garden sites. If the site is compacted, wide holes can give temporary advantage to a newly planted tree, but the width of the hole will be the size of the “pot” the tree will have to grow in. So it is better to modify the site first to take care of compaction and then you will not need a wide hole.

Root barriers do not function well in most landscapes and lead to the development of landscape trash. They can also create root defects

Root barriers were very popular and are still specified today.  They actually do not usually achieve thier goal of preventing surface roots and protecting infrastructure.  Trees outgrow root barriers and they result in increases of landscape trash/pollution.  Root barriers can also create root defects such as circling and girdling roots.  Do not install root barriers, if you are tempted to do so you are likely not choosing a good site to plant a tree.

Cover the roots with backfill from the hole. Do not modify the backfill. Research does not support adding amendments to planting holes for trees. The native soil is what the tree will be growing in ultimately, and there is no reason to modify it. If the soil at your site is so bad that it needs to be changed, this should be a site-wide soil modification that will cover all the area the tree roots will explore up to its maturity. Most gardeners are not able to do this. Roots rapidly expand beyond the planting hole within months, so the time and benefit derived from an amended planting pit is minimal. Adding amendment, especially organic amendments to backfill can also be disastrous for trees. The organic material may utilize nitrogen in the soil and lead to a deficiency in the newly planted tree, worse, it may break down and cause anaerobic conditions in the bottom of the planting pit. Avoid amending planting holes! Never place rocks in the bottom of the hole—this does not create drainage, but creates an interface that prevents it.

A “lollipop” Tree.  Note the very skinny un-tapered stem, lack of temporary lateral branches and retention of the nursery stake–all bad…. Also note the tree snorkel lurking to the left. Kudos for keeping turf away but not far enough away.

If you have selected a good tree, it will stand without staking. There are three reasons for staking: support; anchorage; and protection. Support is sometimes necessary when a tree is cultivated with a long un-tapered trunk and a lollipop crown. Lollipop trees are often sold in nurseries as they resemble small trees. Trees trained in this manner, will not stand without staking. Loose staking allowing trunk movement will foster development of caliper so the tree can eventually stand without supportive staking. Anchor staking is used for trees that experience high winds and “staked out” with guy wires and a non-constrictive collar. Protective staking is analogous to placing bollards around a tree prevent impact from machinery or cars. Always remove the nursery stake at the time of planting and provide any additional support the tree may need. Many Cooperative Extension services have publications on how to stake a shade tree.

Providing a No Turf Zone around trees will aid in their establishment

Avoid planting trees in lawns. Turfgrass and trees conflict with each other. Trees shade turfgrass which results in a thinning sward and increased disease prevalence. Turfgrass slows the growth of trees in an attempt to limit their shading effects. Turfgrass is a very competitive water user and trees will be deprived of moisture and nutrients if turfgrass is present.  If trees must be planted in lawns, maintain at least a 1 yard radius around them with no turfgrass.

Aeration/Irrigation snorkel tubes do not help trees and result in landscape pollution. Note the original nursery stake still in place and the supportive stakes should have been removed long ago. Mulch needs to be replenished.

It has become a common practice to add irrigation or aeration devices to tree plantings. Sometimes called a tree snorkel these plastic 4 inch U tubes are buried below the root zone. Kits can be purchased from Box stores, and architectural details have been drawn specifying their use. Work by UC researchers showed that oxygen does not diffuse far from aeration tubes. So utilizing tree tubes to increase air flow is suspicious. Some planting details specify adding irrigation to the tubes to force a deep rooted condition in the tree. This places water below the root system, which can dry out and compromise establishment—not a good idea… Worse of all tree snorkels are sometimes installed with no purpose at all other than that was what the planting plan indicated. This is a needless practice and results in landscape pollution. Long term, tree snorkels are ugly, easily broken and provide no useful function to an establishing landscape tree. It is not in the nature of trees to proliferate absorbing roots deep in soil and snorkels will not change a tree’s genetics.

After the tree is set in its hole, and backfill settled in with water, apply a 4 inch layer of arborist chips as far out from the trunk as feasible—at least several feet. The chips will modify the soil improving, chemical, physical and biological properties while conserving moisture from evaporation, preventing runoff, and germination of annual weeds. Generally trees thrive under mulch as it simulates litterfall, or accumulation of organic matter under their canopies. Replenish the mulch as it deteriorates. Finally apply irrigation as needed through the mulch from the surface of the soil. This will help establishing roots, leach salts, and move mulch nutrients into the soil profile.  Avoid companion plantings near the main stem of the tree and avoid piling mulch around the tree stem. Following these guidelines will lead to a healthy and useful shade tree that provides its many services for decades.

Understanding the mysteries of plant diseases: Prevention, Control and Cure (Part 3 of 3 in this blog series)

Understanding the mysteries of plant diseases: Prevention, Control and Cure (Part 3 of 3 in this blog series)

What next?
You’ve done your research and made a diagnosis—now what? Sometimes the plant has to be removed and never planted there again. Start over, do something else.

Some diseases are difficult or impossible to control (virus diseases) especially when they are new or unknown to science.

Controlling plant pathogens or abiotic disorders can be daunting, frustrating, even impossible. As I mentioned in the last blog early detection gives more options for control because the disease has not advanced to a degree where it can not be controlled. Controlling plant diseases is not just palliative (treating your plant’s pain) it involves understanding where pathogens come from, stopping their movement, arresting their development and preventing their spread. Understanding genetics of resistance can offer amazing control of diseases, and finally biological control limits the development and spread of many pathogens.

Virus particles can only be seen with an electron microscope, since signs are hard to visualize, early detection is very difficult. Shown are TMV virions

What Can What Can’t?
There are some battles that can’t be fought or fought easily with plant pathogens. When plants are infected with viruses, there is almost no control option but removal (roguing). All plants likely contain some kind of plant virus; but not all viruses in plants cause symptoms of disease. Dangerous viruses like tomato spotted wilt, impatiens necrotic spot virus, cucumber mosaic virus, or many others, are devastating to their hosts and once infected there is no controlling these. Removing infected plants at the first symptom of viral involvement is prudent but often infections have already spread. Viral pathogens almost always infect without significant symptoms,  and become systemic in the plant before their more

Once trees with root rot show symptoms it is too late for control measures, the tree is dead and will not recover. Here Phytophthora spp. has killed a eucalyptus tree.

devastating effects become visible.  By late season, in most vegetable gardens, viral titre (concentration) is very high in solanaceae plants (pepper, tomato etc) and in cucurbits, both groups are highly susceptible. When perennial plants get viral pathogens there is no cure, and symptoms will increase over time. In orchids, viruses can sometimes be avoided by tissue culturing the meristem (which is usually virus free) to clean up a rare plant worthy of salvation. Sometimes plants are already dead but don’t look it. In the case of root rotted trees and shrubs, leaves may still hang from the tree, may still be green but the tree is beyond salvation, control may not be possible. In general control measures are best conducted early.  And by early I mean before you obtain your plant!

An old adage goes: “An ounce of prevention is worth a pound of cure” This is especially so when there is no cure!.  Prevention as a control technique really involves several factors such as exclusion, quarantine, and maintaining plant health so that plants are not predisposed to disease. The first tenet of control is exclusion. Don’t bring pathogens to your garden. Gardeners are their own worst enemy where plant diseases are concerned. Since pathogens can be seed-borne, come with insects, be already infected in the nursery, or resident in soil, care must be exercised when new plants are selected for your garden. Practice safe plant swapping!  Gardeners sharing plants with each other may also be sharing their respective plant diseases! Be careful where you buy plants, sloppy nurseries with their plants on the ground in standing water is a red flag.  Also be on the look out for weeds in nurseries since they can harbor insects that vector virus diseases. Plant debris left on the ground and not cleaned up, can be a source of fungal spores.  So consider the source when selecting plants for purchase.  Inspect plants carefully before purchase, especially slipping the container off to look at the root

All plants should be inspected carefully, especially root systems. Always remove a sample from containers to inspect. Here cyclamen are shown with root rot.

system. I don’t purchase anything (even boxed trees) without doing this first. If you are satisfied that you have a healthy plant then you are ready for the next phase of disease control.

Plants are often quarantined before they are released for cultivation or planting. When you bring your plant home, leave it in the pot for some time. Even bedding plants if purchased young can grow for a bit in containers. Remember lack of growth is a symptom of incipient disease.  Observe your new purchase of a few days or even weeks depending on the plant. If normal growth is occurring then move on to garden placement and planting. A little time set apart from other plants, and careful observation, will possibly prevent bringing something bad to your garden.

Once disease is established, and symptoms are apparent, gardeners often turn to pesticides to try to provide therapy. Sometimes fungicides applied to a plant post infection will slow down the spread of the pathogen within or on a plant. Therapeutic approaches can also turn on plant defense systems or enhance them so that the plant can limit the progress of disease. Therapy is usually not an option with most diseases because the pathogen has often gone beyond the point of stopping it by the time disease is recognized.  Some fungicides applied early, can be very therapeutic in turfgrass diseases, blights and powdery mildew diseases. The key to therapy as a control option is to detect the disease early and use an efficacious material that is labeled to control the pathogen you think is causing the disease on a given plant.  All this should be on the label.

Pruning out branches with cankers is a form of eradication.

An immediate response of many gardeners when disease is discovered is to kill the pathogen. This is eradication. Eradication takes several forms. There are eradicant pesticides, that kill the pathogen on contact. Usually these cause some degree of harm for the host since most pathogens have a host relationship that is destroyed when the pathogen is killed. Eradication can also be  or removing plants from the garden that are a source of disease. Picking up and disposing of fallen plant debris is eradicating a source of potential inoculum from the garden. Pruning cankered branches from a tree is a form of eradication.

One of the best forms of disease control is resistance. Selecting plants that resist disease is built in control. Diseases such as rust and powdery mildew have wide ranges of interaction with their hosts. By selecting plants that are resistant, there is no need for other control measures such as sprays. Resistance to plant disease comes as two types. Horizontal or multigenic resistance is partial or incomplete resistance and is conferred by several genes or their interactions in the host with the pathogen. Vertical or complete resistance is resistance conferred by a single gene in the host. Plants with horizontal resistance will get some of the disease but it won’t be overwhelming, often in grains, lack of resistance will result in complete crop failure. Plants with vertical resistance show no symptoms and are completely immune to the pathogen. While this complete resistance is appealing, it is only conferred by a single gene, and the pathogen can easily break down this resistance and cause disastrous disease. Horizontal resistance while not complete, is called “durable” resistance because it takes more time to overcome resistance conferred by multiple genes. The nature of resistance in garden plants is rarely detailed by growers or seed sellers. Often we are lucky to see any labeling for resistance. Crops like rose, crape myrtle and snap dragon are often sold as resistant to powdery mildew or rust and in some cases plant breeding programs strive to incorporate disease resistance into their breeding lines but then fail to label the product as disease resistant!

Cultural control often involves doing the right horticulture. Keeping turfgrass away from the stem of trees, applying arborist chips, planting at the right depth, are all cultural controls for root disease.

Cultural control is using good horticultural practices to limit the development of disease. Since many plant pathogens require a host to be predisposed, we have the opportunity through good horticulture to avoid the disease development. Planting woody ornamentals at the right depth is a cultural control of Phytophthora collar rots.  Appropriate application of water, reduces stress and prevents plants from being predisposed to both root rots and canker diseases. Correct pruning cuts limit the development of decay in trees.  Appropriate horticulture as discussed in the Garden Professors page will go far toward cultural control of common garden maladies.  Proper plant selection is also a form of cultural control. Choosing plants adapted to the growing area climate, and soils selects plants that are less likely to be predisposed to disease. Poorly adapted plants are more susceptible to pathogens and thus more likely to become diseased.

Biological control is the effect of one organism limiting the development of another thus preventing disease. Classical bio-control is when an exotic pest is introduced and there no natural enemies or parasites to regulate it. The pest/pathogen multiplies rapidly killing or affecting a large plant population. Research in the native range of the host looks for native organisms to control the pest. They are brought to the infestation, released and the pest/disease is brought into control. This works well with insects and the damage they cause. It has also been achieved with exotic plant pathogens.  For our native pathogens, there may already be a community of organisms that limit its development.  This is especially true for soil-borne pathogens. This is why the GP professors so often recommend fresh wood chips as mulch.  Fresh wood chip mulches supply carbon for organisms in soil that interfere with soil-borne pathogens; a kind of mulch-mediated bio control for root diseases.

I find controlling diseases is a lot more difficult than understanding or identifying them.  Usually by the time you have observed disease in the garden it is too late to stop its progress. You can take mental notes not to plant that variety again, or prune more diligently etc. but diseases are largely regulated or advantaged by the environment and our good or bad gardening practices. Of course the pathogen has to be present for biotic disease to happen, as we know that organisms don’t spontaneously generate.  Disease control starts with identification then research and finally gardening actions that help prevent, limit or eradicate disease propagules.

Feel the Heat: Temperature and Germination

 

In most parts of the country it is time to dust off the seed starting trays, pick out your favorite seeds, and get a little plant propagation going on.  There’s definitely a lot of science (and perhaps a bit of art) to successful seed starting.  While the process starts (and relies on) the imbibition of water, one of the biggest factors that affects the success, efficiency, and speed of seed germination and propagation is temperature.  Germination relies on a number of chemical and physical reactions within the seed, and the speed and success of those reactions is highly temperature dependent. Respiration, where the seed breaks down stored carbohydrates for energy, is probably the most notable process involved that is temperature dependent (source).   Think of it in terms of a chemical reaction you might have done back in your high school or college chemistry class – there’s an optimum temperature for the reaction and any lower and higher the reaction might slow down or not happen at all.

Thinking of it this way, seeds and germination are just like Goldilocks and her porridge – there’s too hot, too cold, and “just” right.  Seeds are the same way – there’s a “just right” temperature for germination. The seeds of each species has a different optimal temperature for germination with a range of minimum and maximum temperatures for the process.

Why is important that seeds are started at their optimal temperature?

The optimal temperature is the one at which germination is the fastest. This may seem to only have consequences for impatient gardeners, but slower germination speeds increase the days to emergence for the seeds, which in turns means that the seeds and seedlings have a greater chance of failure. The early stages of germination are when seedlings are most susceptible to damping off, which can be caused by a number of fungal pathogens (Fusarium spp., Phytophthera spp., Pythium spp., etc.) that basically cause the seedling to rot at the soil level. These pathogens (as well as decomposers in some cases) can cause seeds to rot or decompose before emerging as well.  That’s why you’ll sometimes see seeds that are slow to germinate (or traditionally direct sown like corn, beans, and peas) treated with those colorful fungicides.  The fungicide gives the seed and seedling a little bit of protection (for a week or so, depending on the product), which is handy if you accidentally sow them before soil temperatures are optimal or if the species is slow to germinate.

If emergence is really slow, there’s also the possibility of stunting or failure due to exhaustion of the stored carbohydrates that the seed relies on until it begins photosynthesis.  So the closer to the optimal temperature the seed is, the faster the emergence and the highest percentage of germination success.

Image of graph showing relationship between soil temperature and seed germination.

What does this mean for home gardeners?

Whether you are starting seeds indoors or direct sowing outdoors, knowing the germination temps can help increase your likelihood of success.  You can find a variety of resources for the optimal germination temperature for your selected crops.  In general, most warm season plants, like tomatoes, peppers, and summer flowers are in the 70-80 °F range.  This is why most of the warm season crops are started indoors – so temperatures can be controlled to higher levels.

For vegetable crops, here’s a good resource for basic germination temperatures.  And here’s one for a few annual flowers.

Many of the cool season crops germinate at much lower temperatures, which means many of them can be directly sown early in the season rather than started indoors.  Crops such as spinach, lettuce, and other leafy greens have these lower germination temps and typically perform better if germinated at lower temps.

Germinating a variety of plants for our 2018 All-America Selections trials

It should be noted that this is for the soil temperature, not the air temperature. If you’re starting seeds in your home, most people don’t keep their homes in the 75 – 80 degree range in the winter.  Many commercial operations use warmed tables or beds for seed starting, rather than heating the whole facility to the necessary temp – it would be expensive.  For home growers, supplemental heat mats can help increase soil temp without having to heat a whole room.  In a pinch, you can even clean off the top of your fridge and keep seedlings there.  It is higher up in the room (heat rises) and most refrigerators create some amount of external heat as they run.

For any seeds that you’re direct sowing outdoors, whether they require higher or lower germination temperatures, you’ll have more success if you plan your sowing around soil temperatures rather than calendar dates (planting calendars can be good for estimation, though).  Investing in a soil thermometer can offer detailed information on the specific temperatures in your garden soil.  Or, if you have a good weather station nearby many of them have soil temperature probes that could give you a good idea of what the soil temperatures are in your region.

Direct-sown lettuce germinating for a fall crop

But don’t let the cool/warm season crop designation fool you – the Cole crops like cabbage and broccoli actually have an optimal germination temperature on the warmer side, but grow better in cooler temperatures to keep them from bolting (flowering).  This is why they need to be started indoors for spring planting, but you can start them outdoors (even trying direct sowing) for fall crops – they germinate in the heat and then slow growth as the temperatures drop.

Understanding mysteries of plant diseases: Diagnosis and Detection (Part 2 of 3 in this blog series)

Something is wrong?

Sometimes its subtle sometimes its not–like here with powdery mildew on coast live oak.

Do you ever have a feeling that there is something wrong with a plant? It’s just not healthy looking, or it has not grown for awhile? As we discussed in the last blog, disease is a process–it occurs over time. When in the disease time-line you notice the process, can be quite varied. Some astute gardeners may know something is wrong before there are symptoms, others may not take notice of the process until the plant is dead. Your disease detection acuity, or disease intellect, is largely dependent on your ability to recognize when the disease process is happening.  Early recognition gives you a chance to interrupt or limit the progress of disease or “control” it.  This blog is all about enhancing your disease detection acuity.  In the last of the series, I will cover what we can do about plant diseases, their prevention and control.

Sycamore anthracnose disease has vein-following necrosis as one of its foliar symptoms.

Symptoms and signs
Plants respond to challenges from a disease agent by producing symptoms. Symptoms are physiological changes in plants which we can see. Yellowing leaves, necrotic (dead) areas of leaves, stems, flowers or roots are common for many diseases. Some symptoms are very subtle. Slowed growth may be the first symptom of a systemic disease that is spreading within a plant’s vascular system or destroying its roots. Some plants can have 75% of their roots killed by pathogens without any visible symptoms on foliage. Most of the time when symptoms are this subtle, the plant is not growing at the same rate it would if it were healthy. Absence of new foliage, short internodes (distance between leaves), lack of initiation of flowers can all be symptoms of disease. Another subtle symptom is an overall color change that takes away a Plant’s “brightness” or healthy glow. I think most gardeners recognize this, but may not associate color dullness with disease. When subtle symptoms are detected, it is always a good idea to check the roots to see if they are functional (not rotted).

Overt symptoms are easy to distinguish. Fire blight is a good example—the bacterium Erwinia amylovora is spread by bees to flowers where it invades the floral nectaries. Bacteria migrate into shoots and stems and turns them pure black.

Early infections of the fire blight bacterium kill the peduncles of flowers

The disease proceeds rapidly in springtime during bloom and the symptoms (necrosis) are striking. Blights, anthracnose diseases, and canker diseases all produce necrotic tissue symptoms that are easily distinguished from healthy tissues. Even root rot is overt if you take the time to look at the roots!

Fungal hyphae of Armillaria fuse into a mycelial mat under the bark of Peruvian pepper.

Signs are the causal agents of symptoms. Fungal hyphae (collectively mycelium) growing under bark or on plant surfaces are easily observable signs. Just like symptoms, signs can be overt or cryptic. Armillaria mushrooms form in large clusters around the bases of infected trees and are easily identified, but the fruiting bodies of canker diseases (pycnidia) are very small and look like small pepper granules on the surface of a dead twig or branch. Plants often form galls (a symptom) that form around insects or bacterial pathogens (signs). Observing plants carefully to look for signs can be quite diagnostic. For instance if you observe the symptom of distorted new growth on your grape or rose and then carefully examine the tissue with a hand lens you may find the sign of mycelium from powdery mildew. Symptoms often develop after signs and many signs only form in the dead tissue or after the disease has produced much damage.

Fruiting bodies appear as black dots in this necrotic coast redwood tissue. Also note signs of white mycelium

Since signs are often reproductive structures of a pathogen, they are very helpful in pathogen identification. Many microbes have signs and cause significant disease but their signs are microscopic and thus hard

Phytophthora mycelium and chlamydospores are impossible to see in garden soil. These signs are not visible in-situ.

to observe.  The mycelium and spores of many Phytophthora spp. that cause root rot of trees, crops and flowers are invisible in-situ.  They can only be visualized by isolation in the lab.

Internet searches and labs
So you have observed symptoms, you think you have signs but are not sure. What next? There are thousands of plant diseases, and we see new diseases at an ever increasing rate as we explore growing new plants in new places.  Accurate disease diagnosis is beyond most gardeners.  Certainly you can narrow things down by looking at google images of diseases listed for the plant in question. But you can also be misled by google searches.  I would trust only University-based web pages, as there is a lot of mis-information from other sites that are inaccurate or outright incorrect in their diagnoses. In many states Cooperative Extension offices have personnel that will look at samples for you, or may refer you to a diagnostic lab that can examine or isolate the pathogen from your plant sample for a fee.

If you go to a lab for diagnosis, it can rapidly degrade into incorrect or inconclusive findings. Lab analysis, isolation and pathogen identification work well if you already have a suspicion of what your pathogen is.  You are just seeking confirmation.   Samples sent to a lab found without pathogens may not not indicate the plant was not diseased.  Samples degrade as soon as they are taken, they may not be examined right away at the lab or they may not have been transported correctly (ice chest away from sunlight). Sometimes pathogens just don’t survive well in samples, and will be hard to detect in lab settings. And most frequently, the lab usually does not get a sample with the pathogen in it.  A good example is branch die-back symptoms on a tree.  So the gardener brings in dead twigs, but the twig dieback is actually caused by extensive root rot.  The gardener never even thought to look at roots, because the twigs were the dead part. The lab of course finds no pathogens, only saprophytic organisms, which it lists and leaves the sample submitter confused and wondering if they are pathogens.   Labs are best used to confirm something you already have strong suspicions about. You have the fruiting bodies (signs) the symptoms match on-line versions of the disease you are looking at, on the same host, and everything seems right, but you want to be sure. Then a lab is useful. Especially if they get a good sample with signs present.

There are some useful test kits that home gardeners can use to confirm their diagnoses.  Lateral flow test strips are available that detect pathogen analytes. These are especially useful in testing for plant viruses and the diseases they cause.  While the cost of each test is low, there is usually a requirement to purchase a number test strips, so the cost can be over $250 to purchase a number of lateral flow test strips. The test for Phytophthora (root rot organism) is quite effective, gives results in five minutes and requires no special chemistry or long incubation periods. Some of these diagnostics are species specific, some like the Phytophthora kits, only detect the genus, not the species of Phytophthora involved. Test strips are specific to the disease at hand, so you would already need to be pretty certain of what you have if you are using these. Like a lab, they can confirm what you suspect.

Another handy way to diagnose disease is to use a host index. This is basically a list of diseases occurring on a list of different plants. Cynthia Westcott published the most important host index for ornamental plants, but it is long out of print now, and no longer published. Her plant disease handbook can still be found occasionally at Library book sales. The host index by Farr and others, “Fungi on plants and plant products in the United States” produced back in 1994 by the American Phytopathological Society is still in use by most plant pathologists because in its twelve hundred pages, you can likely find what you are looking for.

So after looking at symptoms, perhaps some testing and examining a host index, you think you have your diagnosis. So what? What can you do with a diagnosis? Well this is a jumping off point for reading the literature on a particular disease and its causal agents. Understanding the disease, its processes and timelines for disease progression will assist you in building an effective control program for your plant or garden.  At least you can decide if you dig it up and start over, or weather there is a chance of saving your plant and helping it to resist and recover from the pathogen at hand.  Astonishingly, many plants are treated (even by professionals) without an accurate diagnosis.  Know your pathogen and you will know the range of its effects on your garden plant and you can research ways to limit its damage and spread.  Next time I will talk about actions to keep garden plants healthy.

Tuning up for Pruning Up–Care, Maintenance and Utilization of Hand Pruning Tools

A. J. Downer

Fall is passing into winter and the bare sticks in my deciduous fruit orchard are calling to my annual fruit tree pruning chores.  I can prune my entire orchard with very few tools: a good pair of bypass clippers, a similar set of loppers

Illustration 1. Tri-edge saw blades are made from stainless steel and are not easily sharpened. When dull or bent they should be replaced.

(optional) and a high quality “razor” or “tri edge” saw.  Most hand tools require some maintenance especially the clippers and loppers.   Clippers are easily sharpened but modern saw blades can not be sharpened by gardeners. I usually just buy a new saw, replacing the old one when blade eventually dulls or bends from over zealous use (illustration 1).

Illustration 2. To sharpen bypass clipper blades follow the angle of the bevel. Do not sharpen the flat side of the blade

Before using your pruning tools inspect them for signs of damage. Blades should be sharp and straight.  Loppers should have their rubber “bumpers” intact otherwise your knuckles will be smashed after exerting force on a difficult branch.  Sharp tools offer less resistance and actually decrease injury to users. One exception here is with the modern “tri-edge” or “razor” saws. These saws can cut so quickly that you may pass through the branch you are cutting and continue on to some part of your anatomy quickly ripping your flesh open. I have suffered more cuts (some serious) from these saws than from any other gardening activity (although I was recently impaled by a frog metal art sculpture!).  They should be used with careful precision, not with the wild abandon and pruning fervor of the craven academic desperate for real world pruning experiences.  A thick long sleeved shirt and gloves will also help prevent cuts from hand pruning equipment.

Bypass clippers are so termed because the blade passes by the hook. To sharpen these, find the bevel on the edge of the clippers and align a small file to the same angle of this bevel, and file the bevel until you can feel the sharpness with your finger (Illustration 2).  Never sharpen the back side of the bevel—this will create a gap, and every time you cut, a flap of tissue will remain. Back bevel sharpened clippers will require blade replacement or grinding until the back bevel is gone. The hook does not require sharpening, do not attempt to file it. Repeat this process with lopper blades.

When you are done pruning for the day, wipe the blades of your clippers and loppers with an oil soaked rag or apply a few drops of oil and rub it into the blade. Most modern saws blades are made from stainless steel and require no oil protection.

As a Cooperative Extension Advisor, one of the most common questions I receive is: “Should I sanitize my clippers between cuts or between uses on various plants?”.  Indeed, many publications, extension leaflets, gardening columns, and other sources make broad recommendations to sanitize clippers after every cut. Some articles even compare various products for their killing efficacy.  Blind recommendations are often made to sanitize clippers when the pathogen is not  known or specified.  It is not necessary to sanitize your clippers when pruning most garden plants and fruit trees.  There are a few pathogens that are spread by moving plant debris, but published evidence that they are spread by hand pruning equipment (especially clippers) is nil. One exception is palm wilt caused by Fusarium oxysporum f.sp. canariensis which is easily spread by saws. Some of the canker fungi caused by Botryosphaeria can also be spread by pruning equipment. With many of these pathogens, a wound is required for infection so it may not be that the clippers are spreading disease so much as providing an entry point (infection court) so that pathogens have a way to enter.

If diseases are present in or near the plant already, sterilizing pruning equipment will simply provide a clean entry port for the pathogen—infection can still follow after the cut is made with a sanitized tool.

In my garden, I never sanitize clippers between cuts.  However, conditions vary across the US, and in some places rain, humidity, and temperature are more favorable for disease development.  If you have concern about spreading pathogens, prune during the dormant season, when the likelihood of pathogen activity is lowest. Apply dormant sprays containing copper to limit the onset of new fungal diseases that may enter pruning wounds.  If you still feel you need to protect wounds from dirty clippers I like to use the flame from a plumber’s torch to sanitize.  A few seconds along the cutting edge front and back kills all pathogens (Illustration 3).  The process is similar for a saw but efficacy is increased if the saw gullets are wiped clean with a cloth and then the flame applied. The only time I take these measures is when I know I am working with plants that can be inoculated by pruning (which is rare).


Illustration 3. A plumber’s torch will rapidly sanitize saws and blades when pathogens are present in plant tissues.

When pruning garden plants, there are a plethora of recommendations on how to make cuts. Rose experts have extolled the virtues of an angled cut so water runs away quickly, flush cuts used to be recommended by arborists as the highest quality cut. These examples are without research foundation. Cuts on woody plants should made to create the most circular exposure that leaves the smallest surface area possible. We abandoned flush cuts many years back because they cut into protective zones that limit decay in trees. Some gardeners feel compelled to cover their cuts with a pruning paint and there is a similar paucity of research to support this practice. Leave pruning wounds unpainted.

Grow Garlic – Keep the Neighborhood Vampires at Bay

While most of those gardening tasks are coming to an end, in most parts of the US it’s time to think about planting a few things in the veggie garden to bring a flavorful bounty next year – garlic (and a few related alliums).

I often reference Halloween and vampires when I talk about garlic, not just because traditional lore says that garlic repels vampires, but because it is a good reminder of when to plant garlic in the garden. October is the prime time for adding the alluring allium to the garden. You can also remember that you plant garlic during the same period that you plant spring flowering bulbs.

Why do vampires hate garlic?

Yes.  Vampires are fictional (unless someone finds some empirical evidence of their existence, since you can’t prove a negative 😉 ).  These bloodsucking creatures of folklore may actually have a basis in fact that could explain their aversion to garlic. Way back when people didn’t have science to understand things, they often invented explanation for things that were supernatural.  Sometimes these explanations may have actually had some truth to them.

In this case, the symptoms of vampiricism could have evolved from the symptoms of porphyria – a set of rare disorders of hemoglobin (there’s the connection between vampires and blood).  Symptoms of porphyria include shrunken gums (that could make teeth look like long fangs), painful sensitivity to sunlight, and….and averse reaction to garlic. The reaction comes from the effect of garlic on the blood – it can stimulate red blood cell turn over and increase blood flow, both of which can exacerbate symptoms of porphyria and cause acute, painful attacks.  There’s also an allegorical connection – vampirism was considered a disease (or represented the spread of disease in some literary cases) that was spread by a causal agent and garlic was seen as a curative for disease (it does have some antibacterial properties).  Note: other possible symptoms of porphyria can be excessive hair growth in random areas of the body, which gives it a connection to lore around lycanthropy.

On to the gardening

Now that we’ve covered some trivial, albeit interesting, info lets get on with the gardening!

While many people are accustomed to the single variety available in grocery stores, there are several different types of garlic that all have different flavor characteristics. These types can be classed in two categories; hardneck garlic has a hardened central stem when it dries, and softneck garlics remain soft and pliable. Softneck varieties are the ones that lend themselves to being braided into those hanging garlic braids. Softneck varieties are also longer-storing than hardneck varieties.

It can be tough to find garlic in local garden centers to plant. Those that do carry garlic, often carry it at the wrong time of year for planting when it is shipped in on the spring garden displays. If you don’t have friends to share their garlic with you, or a local farmer to buy some from, you are going to have to go the mail order (or online order) route.

Once you have your garlic bulbs, split them up into cloves, being sure that you have a piece of the basal plate (the part that holds them all together) on the clove. This one clove will turn into a whole bulb over the growing season.

Plant the cloves tip up about 4 to 6 inches apart and about 2 inches deep in loose, organic soil. Mulch after planting with about one inch of straw or shredded newspaper.

Garlic is a relatively heavy feeder, so it would benefit from a good balanced fertilizer treatment with nitrogen after it is established. You can also plant them in the garden where you grew beans over the summer – the bacteria that colonized bean roots adds nitrogen to the soil.

After that, just be patient. It may pop up before winter if the weather is mild, but don’t worry – it can survive even if a freeze kills the growth back to the ground.  Garlic requires little maintenance, and only requires water if the weather turns very dry. Harvest it once the leaves start to die in mid-summer (around July, unless it is an early-maturing variety). Be sure to save some to plant next year and store the rest for use in the kitchen.

Aside from garlic, there are some other odoriferous onion relatives you can plant this time of year like shallots and perennial onions in the vegetable garden or edible landscape.

Shallots have a mild onion flavor and are great because they form cloves like garlic (meaning you don’t have to cut up a whole bulb if you just need a little bit) and store well. The beauty of shallots is that they can also be planted in really early spring — they are a multi-seasonal crop. You can also start them from seeds in the spring.

Shallots are technically perennials, as they will grow over many years if left undisturbed. However, to harvest them, you have to dig them up so they are usually grown as annuals. Once you dig them up, use the larger bulbs for cooking and save the smaller ones for replanting.

Multiplier onions, sometimes called “potato onions” are another fall-planted perennial. These plants produce clusters of bulbs (hence the name “multiplier”) that are harvested in the early summer for bulb onions.

One of the benefits of these and other perennial onions is that you can harvest the green blades of the plant for use as green onions or scallions throughout most of the winter and spring.

Egyptian walking onions are another perennial that can be harvested either for its bulb or as a green onion. The name comes from the bulbils that form at the top of the flower stalk. When they mature, they get heavy enough for the stalk to collapse and fall over, creating a new bunch of onions away from the mother plant. You can allow them to do this to fill in an area, though most people limit it by harvesting the bulbils before they fall.

There are also perennial leeks that have a flavor similar to leeks and can be harvested as green leeks through the winter or dug up as small, tender leeks in the spring.

If you love growing perennial vegetables that add flavor to just about any dish, give these tasty plants a try. They’re really simple to grow and can keep your garden and your kitchen full of fun and flavors for years to come.

A quick primer on types of garlic

Hardneck Varieties

  • Purple Stripe — bulbs have purple on the outside. Some of the tastier garlics that become deliciously sweet when roasted.
  • Porcelain — popular gourmet variety. Usually has a more robust and spicy flavor. Bulbs are typically large and have large cloves.
  • Rocambole — Rich, complex flavors popular with chefs. Their scapes (edible blooms) form a double loop. They do not do well where winters are warm.
  • Asiatic/Turban — Do not store for long periods. Mature earlier in the season (late spring as opposed to summer) than other types. Flavors are usually strong and hot.
  • Creole — Attractive red color. Performs well where winters are warmer. The flavor is similar to (though milder than) Asiatic/Turban Varieties.

Softneck Varieties

  • Artichoke — the grocery store garlic (California White) is an artichoke garlic, though other varieties have more complex flavors. Bulbs tend to have multiple layers of cloves.
  • Silverskin — often the last in the season to mature, these are the longest-storing garlics.

Elephant Garlic

This is a common “garlic” planted by many gardeners because it has large, easy to use bulbs with a garlicky flavor.  Though it is technically not a garlic species – it is a type of perennial leek.

Root washed perennials – 3 months later

You’ll recall that in July I posted about root-washing perennials before planting them in the middle of our typically hot and dry summer in the Pacific Northwest.  I wanted to update everyone on how they performed now that we’re heading into our cooler and wetter fall months.

Just to remind you, here’s a photo of the garden right after planting:

South-facing pollinator garden

And here is the same garden, 3 months later:

Made it through the summer!

No plants died; in fact, as you can tell, they all thrived. They were watered twice a day during the hottest months and now are rain watered only.  (The underlying soil is an excessively drained glacial till, which is why we water frequently during esablishment and why we don’t worry about the drainspout. Water doesn’t stay around long.)

I used no fertilizer. I did add the soilless media from the root washing to the top of the soil and then covered with woodchip mulch.

There was, of course, a period of about 6 weeks post planting where there was no above-ground growth. But all of these plants retained their flowers, which kept our bees and other pollinators (butterflies and hummingbirds) happy. In August, the plants started to put on new growth at a furious rate now that roots have established.

Native bumblebee on salvia.

Take some time and go back to the original post (which is linked in the first sentence. Look at the roots – before and after washing and pruning. Now look at the results.

Why wouldn’t you plant this way?

My cucurbits won’t stop having sex.

Not really a botanically-correct statement, but you know what I mean. John Porter’s previous blog post did a great job of explaining cucurbit reproduction (loved the Pucchini). Though I was surprised to learn “not getting any fruit” is actually a problem. Can’t say I’ve had an issue with that, ever. We have a really vibrant bee population and they’ve been super busy.

I love growing squash of all sorts, despite not being a terribly gifted vegetable garder. Past Garden Professors posts have addressed this issue. One might ask, why on earth would a two-person household need a 60-foot-long row of zucchini? Because we can!  Though if I recall, I intended to go back and thin the row. Whoops.

The zucchini hedge. And those aren’t weeds, they’re *biodiversity*.

By late summer, we usually end up with gummy stem blight, powder mildew or squash stem borer  No sign yet, though any of these goodies could show up next week. The plants are all healthy and ridiculously enormous. It’s been very warm and dry, but we have a nice drip irrigation system in place.

So guess what happened when we got too busy to check on them for three days?   Many more were still on the plants when I snapped this pic. I’ve worked zucchini in some form into every meal except breakfast. Joel’s still being a good sport. Next step is anonymous *gift* bags to folks at the office. Though I think I’m getting a reputation.

Normal-sized zucchini at top of photo for reference.  Aargh.

Not all zucchini taste alike, as true fans know. The pale hybrid Bossa Nova, right, has very creamy and tender flesh with seeds that are really only noticeable when it gets, er, hefty. Bossa Nova is a recent All-America Selection and perfect for use with those spiralizer thingies.  The ribbed/striped variety is Costata Romensco – an heirloom variety with really wonderful flavor. Humongous plants though, probably not the best choice for square foot gardening fans. Tigress is the white-flecked green selection, allegedly more disease resistant than most. Bright and sunny Gold Rush, an old-school AAS selection, adds some color and is a bit sturdier/keeps longer than yellow summer squash.

I won’t be trying to save seeds – as John noted, can be very tricky/futile when there are other cucurbits about. Plus it’s too much fun to pick out next year’s selections from the winter seed catalogs, when the prospect of bountiful zucchini stacked like firewood actually sounds appealing.