I’ll be the first to admit it: I am a neat freak. I work best on desks with little clutter and feel calm and relaxed in spaces that are well-organized. But outdoors, it’s a different story. Dynamism is in charge and it’s refreshing and exhilarating to be surrounded in nature’s chaos. So this time of year can bother me when I see gardeners putting their neatness imprint on their gardens – especially onto their soils.
If you Google the word “soil” and look at the images that pop up, nearly all of them look the same. Nice, dark brown, granular stuff, often lovingly cradled in a pair of hands, that really looks more like coffee grounds than soil. In fact, the only realistic picture in the first page of images comes from the Soil Science Society of America. THAT’S actual soil.
So gardeners must discard the “tidiness ethic” that seeps out of the house and into the soil. Soils are living ecosystems, and living ecosystems are messy. A living soil will have some sort of organic topdressing (mulch) resulting from dead plant and animal material that accumulates naturally. In temperate parts of the world, this happens every autumn, when leaf fall blankets the soil with a protective and nutrient-rich, organic litter. And what do we do? Why, we rake it or blow it and bag it and toss it. Then we turn around and buy some artificial mix of organic material and spread it on top – because it looks nice and tidy.
Let’s stop this nonsensical cycle. Stop buying plastic bags for leaf disposal. Stop buying organic matter for mulch. Instead, use what nature provides to protect and replenish your soils. This doesn’t mean you have to leave messy piles of leaves that blow around rather than staying put. Instead, shred them! They look nicer, they stay in place better, and they break down faster. The easiest way to do this is to either run a lawnmower over them, or to put them into a large plastic garbage can and plunge a string trimmer into them. (Bonus – if you use a battery-operated mower or string trimmer you reduce your fossil fuel use.)
Likewise, if you have twigs, prunings, and other woody material, save these too. A chipper is a useful, though expensive, purchase. But those woody chips are the best mulch you can use over your landscape and garden beds. Most plants rely on mycorrhizal fungi, and these fungi require a source of decaying wood to function optimally. The chips can go right on top of your leaves to keep them in place and add a slow feed of nutrients.
So this fall, see how much of your garden’s refuse can stay
on site. Compost soft materials; shred dead leaves; chip woody material. You’ll
reduce your contribution to the landfill, and improve the health of your soils
and plants alike.
Here in California we had an extreme heat event on September 6, 2020. In my yard temperatures peaked at 120 degrees F. This also happened back in 2018 earlier in the summer where we reached a similar peak temperature. It is not supposed to get to be 120 degrees F. in Ojai. This year new high temperature records were set all over southern California for the month of September. Following these heat extremes, wildfires have spread from border to border (Canada to Mexico) in western states. As we suffer through heat and flames here in Western US states, we are also now told that this is a la Nina year so Southern California will continue with drought conditions into 2021. Extremes in climate bring hot dry weather to the Western United States and hurricanes and drenching rains to the eastern United States. Plants in landscapes may or may not be adapted to these extremes.
My poster child heat monitor is the coast live oak, Quercus agrifolia. When temperatures exceed triple digits >110F, foliage on this native oak turn brown and burn on the south exposed canopies. They are not adapted to these record temperatures. This can be evidenced by looking at the damage throughout many California communities. Coincidentally other non-native plants are better adapted to high temperatures. The California pepper or Peruvian Pepper (Schinus mole) does fine in 120F weather with no irrigation. Eucalyptus of several species also have tolerated these increased temperatures. Trees that are drought stressed from lack of irrigation after a long dry summer will sunburn more severely than the same plants under consistent irrigation. If you see this kind of damage, its best to leave it alone until the plant responds by growing new shoots.
While study of “climate ready” trees is giving us tree selection options for hotter climates, the research is still new and we have many other species to consider beyond what has been recently reported. Of the species I have in Ventura County few of our study trees showed any damage from the extreme heat, and only the very youngest leaves were damaged on western hackberry and Catalina Cherry. Pistache, Island Oak, Palo Blanco, Tecate cypress, Arizona madrone, and Ghost Gum were not affected by triple digit weather this September. Other ornamental species that were damaged all over Southern California include the following: Avocado, Camphor, Privet, Magnolia, Coast Live Oak, Sycamore (especially the native Platanus racemosa), loquat and ornamental plum.
It our recent heat damage surveys I have observed that Coast Live Oak and Western Sycamore, two native trees that enjoy widespread tree ordinance protections were consistently damaged by our hot day early this month. If we continue to have extreme hot days, poorly adapted native trees will be injured more frequently, and possibly become more susceptible to damaging insects or native pathogens. This tends to restrict the range of natives to areas they are still adapted to growing in or grow into a new region where they are more successful. A time may come when a native tree is not the best choice for your area.
McPherson E.G., Berry, A.M., van Doorn, N.S., Downer, J, Hartin, J., Haver, D., and E. Teach. 2020. Climate-Ready Tree Study: Update for Southern California Communities. Western Arborist 45:12-18.
This topic may have no relevance to where you live – but it’s very much front and center here in western Washington this summer. Our naturally droughty summers have gotten longer, hotter, and drier thanks to climate change. Wildfires are ravaging all of the west coast, on both sides of the Cascade mountains. And one of the recommendations I see for fire-proofing your landscape is to remove all wood-based mulch. While this might seem logical, it’s not. And here’s why.
Not all wood mulches are equal. Wood chip mulches, which readily absorb water, are different than bark mulches, which can be quite impervious to water based on the type of bark and how fresh it is. The waxy components of bark not only make it resistant to water movement, they also more likely to burn. Likewise, pine needles, cones, straw, and other coarse organic mulches absorb little water and easily ignite. They should be avoided in fire-prone areas.
Wood chips are one of the least flammable mulches, and if landscape plants are properly irrigated, the wood chip layer is going to be increasingly moist as you work your way down to the soil. This reduces flammability, while maintaining plant health. And healthy plants are more likely to survive fires than water-stressed plants – because they are full of water. (Oh, and those “flammability lists” of plants you might see? Dr. Jim Downer has already debunked that approach.)
The best way to reduce wildfire damage to your planted landscape is to keep it irrigated. Bare soil is a no-no in planted landscapes, regardless of what you might see recommended elsewhere. A well-hydrated landscape with green lawns and healthy trees and shrubs is not going to catch fire from a spark or ember. And it might even survive a fast-moving wildfire.
We saw this in eastern Washington this week, where the small town of Malden was 80% destroyed by a fast-moving fire. But some homes were spared – why? Whitman County Sheriff Brett Meyers pointed out “those people that had some green and some buffer around their home were able to maintain their homes.”
So while it may seem counterintuitive to keep woody debris on your soil, look at the whole system – not just a piece of it. If you don’t have plants anywhere near your house, then bare soil is the way to go. But for planted landscapes, wood chip mulch is part of the solution – not the problem.
Summer is here in the west in a big way. We are just coming off of one of the largest heat waves ever recorded, and while temperatures are down they are not done. Its hot. Depending on where you live your gardens may have suffered. In the East Hurricanes are starting and extreme rains are occurring. I have images of bent over palm trees in Florida. No matter the season, plants respond with their own growth stages providing they are not blow away or burnt up by raging wildfires. Here in Arizona we have had moderately hot weather in my location but the garden is surviving with irrigation. My Iris plants remind me that it is long past time to deadhead and remove spent flower stalks. Deadheading is second nature to most gardeners and other than making the garden look better, you may not realize why you have or have not adopted this common garden practice.
Deadheading involves removing the spent flowers or inflorescences have withered. Sometimes pruning back to a lower leaf or adventitious bud in the case of roses, or completely removing flower stalks in the case of German Iris is required. The immediate result is a neater looking garden and an emphasis on remaining blooms. When the dead flowers are gone the remaining flowers look better the garden is refreshed. Depending on the plant there can be other benefits if deadheading is done consistently and is well timed.
We grow many kinds of plants in our gardens and deadheading has varied physiological impact depending on the subject being pruned. Properly timed, deadheading can extend the bloom of some plants for example Calendula. However, Calendula produces lots of flowers and removing spent flowers can become an enduring task if you have a lot of Calendulas. Deadheading some garden plants seems pointless such as impatiens which just regenerates flowers on its own. Deadheading soon after a flower passes prevents the plant from investing energy in seed development. If the plant has a long enough bloom cycle, so that energy can be put into other flowers then trimming back the flowering stem stems that are destined to fruit production often releases other buds to grow more flowers. Since photosynthate (sugars) flows in plants on a source-sink model, taking away the “sink” or developing fruit allows energy to be used for growth elsewhere in the plant. The trick is to remove spent flowers soon because seed begins to form immediately after flowering and the plant will rapidly allocate its energy to reproduction once the flowers are pollinated.
Not all garden plants respond to deadheading–the number of flowers some plants present is genetically regulated and dead flower removal does not promote more flowering (many bulbs produce only one set of flowers). Other garden plants will re-bloom if given a chance, and with deadheading (no matter what the flowering habit) the garden will look better without the dead flowers. Some bulbs can be deadheaded to prevent seed formation so that the energy is put back into the bulb or bulblets for next year’s display. Many roses will re-bloom after deadheading. This is not a wild-type characteristic of roses but a quality that has been selected for after years of plant breeding.
Deadheading can also be an excellent method of excluding diseases. Botrytis on rose blossoms and petal blight on Camellia are both controlled to some degree by removing infected blooms as soon as they are observed and disposing of them away from the garden.
Sometimes deadheading results in seed collection. Left too long, some plants go to seed but have not yet released their seed. If you want to save seed for propagation, strategic deadheading will allow you to collect seed while redirecting the plants growth patterns for more vegetation or more flower shoots. It is also helpful with our more ruderal garden friends to remove flower stalks to prevent their reproduction and taking over of smaller garden spaces that endure frequent cultivation or soil disturbance. Some plants are desirable but their progeny are a bother….
It’s the middle of summer, and maybe you’re wondering what’s wrong with your landscape tree (or shrub) that just doesn’t seem to be putting on the growth that you’d expect this time of year. Before you take any “corrective” action, let’s figure out what the problem might be. Here’s a short checklist that we will start with. (NOTE: This is just a start. You can go so many different directions once you have some specific concerns to explore.)
Soil information. Have you had a soil test done in the last few years? If so, are there any nutrient toxicities indicated? Has the soil been significantly disturbed or modified in the last several years? Have you recently added any chemicals (fertilizers and pesticides, organic or otherwise) or amendments?
Plant information. When was the plant installed? Was it in a container or in a burlapped rootball? If so, were all materials removed from the roots by root washing before planting?
Planting information. Did you amend the soil (i.e., add anything to the backfill) prior to planting? If so, what did you add? Did you mulch it afterwards? If so, what is your mulch material? Did you ensure that your plant was set at grade in the landscape? (“Grade” means that the root flare is at the soil surface.) Did you water it in well and avoid compacting the soil? Are new plantings adequately irrigated during their first year in the landscape?
Environmental information. Have there been unusual weather events between time of planting and now? Is there sufficient irrigation and drainage?
Symptoms. What are you seeing that concerns you?
At least 95% of the landscape failure cases I’ve diagnosed over the last
20 years can be traced back to improper planting methods. You simply cannot
pull a woody plant out of a pot and stick it in a hole. There are three major
factors at play here to consider when rootballs are planted intact:
The textural and structural differences between the soilless media around containerized roots (or the clay in a B&B rootball) and the soil in the landscape are significant enough that they will impair water, air, and root movement across the interface. This means roots have a difficult time establishing outside the planting hole.
Any structural flaws in the root system created during improper potting-up at the production nursery, such as circling or J-hooked roots, are undetected and uncorrected. And these woody roots will stay in a death spiral after planting.
If you cannot see the root flare of your plant, then you cannot plant at grade. Most trees and shrubs that are buried too deeply will generally fail to thrive and eventually will die.
If you’re like the majority of people who are seeing problems this time of year, you know that improper planting or severe soil disturbance is to blame. But now is not the time to fix it! You’ll need to wait until the fall, when the crown has gone dormant, to dig the plant up and take corrective action. (The “corrective action” has been discussed in this blog before; you can explore the archives or wait for an upcoming post).
What you want to do right now is keep your plant as healthy as possible by mulching with coarse wood chips (not bark) and supplying them with adequate water. You DO NOT want to prune them, because that just uses up stored resources as the plant then replaces pruned material with new shoots and leaves. You DO NOT want to add fertilizer, unless you know that you have a nutrient deficiency (which you can’t know unless you’ve had a soil test. And no, those cute little diagrams of what nutrient deficiencies look like in corn leaves are worthless. You’re not growing corn here.) And DO NOT add any pesticide of any sort, even if you see signs of insect or disease damage on the foliage. With few exceptions, pesticides are broad-spectrum and you will kill beneficial species as well as any possible pests. Opportunistic pests and disease attack stressed plants, and that’s why you are seeing them.
In the upcoming months, I’ll do some follow up case studies that can help you learn how to diagnosis problems. If you’re interesting in having your tree or shrub problem diagnosed and can supply sufficient information (as outlined above) and clear photos, leave a comment on this post and I’ll contact you.
Terrariums are are contained environments that allow culture of plants. They take many sizes, shapes and dimensions and can be sealed or open. At the least terrariums are just plants in a bottle, in their highest form they are cultivated landscapes in miniature. Closed terraria create a unique environment and opportunity for plant growth. The transparent walls of the container allow for both heat and light to enter the terrarium while maintaining high relative humidity and preventing system water loss. Sealed containers combine retained moisture and heat which allows for the creation of a small scale water cycle. This happens because moisture from both the soil and plants evaporates in the elevated temperatures inside the terrarium. Water vapor then condenses on the container walls and eventually drips back onto plants and soil below. A sealed terrarium is ideal for growing some kinds of plants due to the constant supply of water, thereby preventing them from becoming dry. Lowland jungle plants from warm climates will do well. Some cloud forest plants, orchids and bromeliads will not fare well in sealed environments because they require more air movement and/or cooler temperatures. Terrarium culture can allow growth of plants difficult to cultivate even in greenhouses. Terrariums can be displayed to great effect and are an easy method of indoor gardening. Success with a terrarium garden requires an understanding of the container, light, media, and the plants themselves.
A Word about the Plants
A contained environment is not for all plants. When in a sealed environment, certain plants such as cacti or succulents will grow poorly or in a manner not suited to their habit (lanky or etiolated growth). Problems arise when plants not suited to a small contained environment are used. Plants such as Syngonium, Diffenbachia, and the larger Peperomia spp. look good when planted initially, but will soon outgrow their space–they are not suitable for closed terrariums. The classical “florist” terrarium planted with very young houseplants looks good at first but is completely unsustainable for months or years. A well designed terrarium should grow for multiple years before a complete tear down and replant is necessary. Thus it is necessary to select truly miniature and high-humidity-loving plants for closed terrarium culture. Ferns, sellaginellas, gesneriads, begonias and some peperomias are suited for these conditions. Obtaining truly miniature and humidity loving plants is difficult. Online vendors are the most accessible sources, but also other hobbyists or plant societies can be sources at their annual sales. Nurseries carry some of these plants but the vast array and diversity of rare plants are found on Ebay and Etsy. Many nurseries list plants under the ‘terrarium plants’ search words that are not really suitable, so take care to look for truly small or miniature plants. Perhaps start with the list I have provided at the end of this article for some of the tried and true plants that will work well. Terrarium gardens are not sustainable if you make bad plant choices, you will eventually end up removing plants that outgrow their containers.
Once you have your plants, you are ready to start. Or you can start before getting your plants and set up your terrarium now to plant later, or in stages, as you acquire new specimens to add into your contained garden. The first consideration is a suitable container. The larger the container the easier it will be to plant, grow and maintain your garden. Larger containers will also allow for a greater diversity of plant types. Fish aquariums may not be the most attractive, but are the most practical in many ways. Because they are rectangular they allow for placement of a light on the lid and they are easy to cover and place on square surfaces such as tables or window sills. Glass containers are preferred over plastic because they maintain transparency better over time. While bottles are attractive, if you can not get your hand inside they can be very difficult to plant and maintain.
Lowland, humid jungle plants grow in decomposing organic matter. For our purposes peatmoss is the best medium. It can be amended with fine horticultural perlite (20-30%) or sand. Sand will make a heavier mix, and, if you are doing a large terrarium, mix weight is important. If not, sand is ideal. Also, since terrariums are contained, they may become disease gardens if you are not careful. Therefore I recommend sanitizing your media in a microwave until the media temperature exceeds 160F. Keep the bag closed until the media cools. A turkey roasting or other microwave safe bag works well. Media can be sanitized in a conventional oven–it just takes longer. Media should be moist but not wet when microwaved. Distilled water can be added later to moisten the media after planting. Commercial mixes can be used for terrarium media but care should be taken. Search the blog for my article on potting soils.
Since terraria are sealed environments, you need a reservoir for the water and a filter. Create the reservoir with coarse horticultural perlite (#3) up to an inch thick (the bottom most layer) depending on size of the container –the bigger container, the thicker the layer. Cover the perlite with activated charcoal. Fish aquarium charcoal or horticultural charcoal from the nursery is fine, but NOT charcoal briquettes. The charcoal layer just covers the perlite. Now add soil. Slope the soil from thin in the front to thicker in the back. You can also add wood, sticks, and rocks to make interesting landscapes. They should all be sanitized in the dishwasher or boiled or microwaved until sterile. After placement of soil, rocks and sticks are ready to plant. Place larger growing plants in the center and rear and small vines up front.
Your container should be sealed either with “cling tight” plastic wrap or glass. I prefer glass for most applications.
While terraria can grow in window light, especially north light, it is not optimal for most plants and they will grow slowly. You can’t place terraria in direct sunlight or the plants will “cook” because closed terraria can’t dissipate heat that rapidly. The old standard for light sources is fluorescent tube fixtures, but they have been supplanted by Light Emitting Diode (LED) technology. Grow-light LED fixtures are expensive, but provide some performance differences. Terrariums are not crops and we don’t want them to grow too fast so find an affordable light source that works for you. LED sources are nice because they are not bulky and do not add large amounts of heat. A bit less light or less optimal wavelengths of light are ok because we want to sustain plant growth for a long time, not grow the plants to the edge of the container real fast and have to prune or start over. The Costco brand shoplight LED fixture is perfect, but it is four feet long. Smaller LED fixtures would be appropriate for smaller containers. The Costco fixture is perfect for a 60 gallon fish tank. White light works well and looks best. Red and blue LED fixtures change the way we see the plants and are not best for viewing. Light should come from above so plants will appear to be growing normally. If the terrarium is placed near a window it will need to be rotated to keep plant growth even.
Moisture is critical in terraria. The growing medium should hold a shape when squeezed but not be saturated when you plant. After the terrarium is planted, you can “water it in” with a dilute -1/4-strength fertilizer solution mixed into distilled water. Watering amounts will vary by container size. Water should penetrate soil to the depth of roots and some should enter the reservoir. No more watering is necessary again until some time later when plants have grown considerably—usually months later. I usually water the glass to clean it from the initial planting with a turkey baster. At some point in the future, months not weeks, the soil may dry as growing plants use up water. When this occurs, water again with another dilute fertilizer solution. Do not over water your terrarium or bad things will happen. Also resist misting or spritzing as this will cause leaves to rot and is not necessary in a sealed environment.
Pruning, Replanting and Maintenance
Some of your chosen plants may outgrow their space. Some like Ficus minima ‘quercifolia’ will just overgrow everything, the same can happen with common Sellaginella sold in nurseries such as S. brownii. You should plan on pruning back the plants and making cuttings or planting other terrariums with the prunings. Cut begonias below a node or along the rhizome. Rhizomatous ferns can be clipped or dug and planted elsewhere. If you have to remove a really big plant it will leave a hole. New sterilized mix should be added to fill the hole along with the new plant occupant. Removal of flowers, mushrooms (should they form) and dying leaves is important. They will cause rots on plants they fall on. Sticks are usually always a problem since it is very difficult to kill mushroom fungi living in them. Mushrooms are mostly non-toxic to plants, but they drop spores and these lead to rot on sensitive begonias and ferns. Clip back Begonia, EpisciaSellaginella, Peperomia or Ficus to prevent them from overgrowing other plants.
Recommended Plant List
If you can find them, here are some recommended plants for terrariums.
Begonias B. prismatocarpa B. prismataocarpa variegata B. versacolor B. ‘Raja’ B. ficicola B. exotica
Ferns Edanoya spp. Humata parvula Lemmaphyllum microphyllum Microgramma spp. Pecluma pectinata Tectaria spp. Quercifelix zelanica
Others Peperomia prostrata Sininngia pusila and all its variants Episcia spp. (there are many, I like the pink ones) Saintpaulia (african violets-only miniatures) Sellaginella erythropus Sellaginella spp. (there are many kinds, S. brownii is most common) Ficus minima ‘quercifolia’
It’s not my week to post on the blog, but this is a PSA for California residents. Having visited the Capitol grounds in Sacramento, I find it important to make others aware of the plans to remove a number of large and historically important trees for the purpose of building a parking garage and expanding the Capitol building space.
I’m not a California resident, so in a sense it’s none of my business. But I am an urban horticulturist, and an arborist, and committed to preserving trees especially in urban environments. These trees are irreplaceable unless you want to wait a few hundred years. The plans to “relocate” some of these large trees are probably not realistic given the size of the specimens.
More importantly, this is public space and the public should be actively involved in discussions. But the process has been secretive and under the radar of a public more concerned, and rightly so, about COVID-19 and all the associated fallout from the pandemic. But it’s not too late.
Please share this post with California residents who have should have a say in how their land should be managed.
More importantly, you should call AND write to your own California legistator at this website findyourrep.legislature.ca.gov, as well as the two Legislative leaders who can really pause the project and guide its re-planning: Senator Toni Atkins, President pro-Tempore of the Senate, 916 651 4039 and firstname.lastname@example.org. UPDATE: This email does not appear to work. Try using this form. Assembly Member Anthony Rendon, Speaker of the Assembly, 916 319 2063 and email@example.com
Two years ago I installed a pollinator garden in early July. This goes against my recommendation to install plants in the fall, when roots have longer to get established and less stress is felt on the rest of the plant. But I wanted to see what would happen if I was careful to mulch well and keep it irrigated. Oh, and did I mention I was going to root wash every one of them? (Be sure to look at that process in the link from 2018.)
I reported on progress last year, and this year shows even more vigorous growth by nearly all the plants. Two of the three ‘Bandera Purple’ lavender died over the first winter, as they were marginally hardy (USDA 7-10) for our area. One straggler remains in the lower right hand corner of the photo below. The Agastache ‘Acapulco Red’ and the Verbena ‘Homestead Purple’ were planted near the front of the beds on both sides and while they survived the first year, they are now gone. My guess is that our cold snap in February 2019 wiped out those plants that were in less protected locations. Perhaps we’ll fill those spots in later with something more cold hardy, or just let the escaped Viola tricolor continue to colonize bare spots.
Overall, the garden is wildly successful in attracting hummingbirds and a variety of native bees and other insects.
I still have a little work to do – I’m relocating the strawberry adjacent to the southeast garden so it stops invading the perennial bed. But after that I’m calling this garden finished.
Summer is a time of bounty in the home garden. During June, July and August the majority of small fruits ripen on home orchard trees. Plant health care is important to consider in advance of summer bounty. Careful dormant season pruning, dormant sprays, mulching and care helped to produce a nice harvest. As the fruit comes off the tree, some summertime options are available. This is a time when some limited summer pruning can be done to manage the physiology and growth of many fruit trees. Even some citrus will benefit from careful summer pruning.
One obvious reason to prune in summer is to repair broken and remove dead branches that may have occurred from excess fruit weight or other injuries. Breakage is common in peach, plum and apples if fruit loads are not thinned earlier in the season. Cut the broken branch from the stem it attaches to with an angled cut that leaves the branch collar intact. Do not cut branches flush with the stem they were attached to. Many years ago the myth of flush cuts for shade trees was found to permanently damage trees, but flush cuts are often still practiced on fruit bearing trees. Flush cuts allow decay organisms to enter trees leading to heart rot and other kinds of wood decay.
Another myth that persists in home fruit orchards is painting wounds with a ‘sealant’ or ‘protestant’. There is no reason to paint cuts. They do not limit the progress of decay or prevent decay from forming behind the paint. Pruning paints do not promote “healing” or callus formation to close the wound. There is some thinking that pruning paints may even accelerate the process of decay formation. So throw away the black tar, it has no practical purpose in support of pruning.
While pruning paints are no longer used, paint has other functions that can be helpful. If a large branch was removed from a tree, sometimes the remaining branches may require protection from sunlight. Apples and other thin-barked trees (citrus, cherries, etc.) are very susceptible to sunburn. If branches that were previously shaded are suddenly exposed to high light levels, the bark can be destroyed leading to sunburn cankers and entry of disease-causing fungi such as Botryosphaeria spp. If repair pruning exposes a large gap in the canopy, it is appropriate to apply white wash or diluted white latex paint to exposed branches in order to protect them from bright sunlight. The most severe damage occurs on southern and west facing branches. Sunburn is one of the leading causes of abiotic damage and a predisposing factor for disease such as stem and branch cankers in apples.
Fireblight is another common disease on pears and apples and develops after bloom. Pruning out fireblight affected twigs helps to arrest disease progress. Finally, bacterial canker can be devastating to Prunus (plum, cherry, peach, nectarine and almond) in parts of the country with warm summer rains. Immediate removal of bacterial canker affected branches is necessary to prevent permanent damage to the tree. Tools used to remove cankered branches should be sanitized by flame (torch) or with disinfectants. Canker diseases are active in the warm summer growing season. Cankers can be caused by bacteria or fungi and should be dealt with as soon as symptoms are noticed. The earliest symptom of an active canker is slowed growth relative to other branches on the tree. Slowed growth results in smaller leaves and fruit and fewer leaves. Affected branches seem more open and just look “weaker” than their healthy counterparts. Slowed growth is often followed by wilt, leaf drop and eventually necrosis or death of the branch. It is best to remove diseased branches early before the organism spreads to the main stem. Since symptoms occur when leaves are on, summer pruning is the best approach to remove cankered branches. Regardless of where or when damage occurs, using correct pruning practices should be adhered to.
Healthy growth on the tree above but thin, weak, small leaves on the tree below indicate a developing branch canker.
Pruning is used most widely on fruit trees to dwarf them so that fruit is produced at a height convenient for harvesting. Pruning creates two universal responses that apply to all woody plants:
I. Pruning is growth retarding. The part of a tree pruned will grow less than the unpruned part. Or, a pruned tree will grow less than an unpruned tree.
II. Pruning is a bud invigorating process. A pruned tree or branch will have more of its buds released to grow compared to the unpruned branch or tree where many buds remain in a dormant state.
The more a tree is pruned, the less its roots and stems will grow. Even though the more a tree is pruned the more latent or axillary buds will be released to grow, it will not be able to make up for the lost leaf potential of the unpruned tree. The pruned tree has reduced photosynthetic capacity, makes less energy and will grow less overall. The thing that is not very clear is how the timing of pruning affects the basic processes. In his review, Chandler makes clear that pruning in the dormant season will retard the growth of apples less than if they are pruned in the summer. Summer pruning also significantly reduces the growth of roots compared to dormant season pruning. Removing leaves in mid-summer or after all shoot growth has stopped (summer rest period), removes photosynthetic capacity and reduces stored energy in the tree, thus retarding growth overall. While buds may be invigorated and new summer growth may occur, this rarely makes up for the tissue lost and still results in growth reduction.
Summer pruning does not result in more fruitfulness the following year, and in apples does not increase the number of spurs formed for fruit formation. Summer pruning can open the canopy and allow branches to form lower down that are useful for easy harvest. The effect of summer pruning on next year’s fruit quality is uncertain. Summer pruning can accelerate the ultimate scaffolding or canopy shape for the mature tree.
Pruning citrus after harvest, during the warm season can affect fruit size in the following year. This may be due to fruit thinning as some citrus have green fruit formed by summer that ripen in winter or spring. Summer pruning removes fruit and remaining fruit can grow larger.
Summer pruning of fruit trees before fruit harvest increases light penetration into the tree and can increase color development of the fruit. Pruning must be done cautiously to avoid excess light penetration and sunburn to scaffold branches and resultant canker diseases. Summer reduction pruning is most often accomplished by pruning the ends of branches back to other branches or twigs. Removing about one half the current season’s wood (on a given branch) will achieve objectives usually without causing excessive light penetration into the canopy. Not every branch need be pruned but an even approach, removing branches consistently around the tree, will maintain form. No more than 15-20% of the canopy should be removed by summer pruning. On some vigorous growing trees such as Persian mulberry, pomegranate, or some peaches, heavier pruning doses can be used. Pears, apples, plums and cherries require less pruning and cuts should be made to preserve spurs and other fruit bearing wood. Some varieties of cherries can become ‘over spurred’ and thinning cuts to remove excess spur wood can sometimes be helpful to limit production and increase fruit quality in the next season.
Chandler, W. H. 1923. Results of some experiments in pruning fruit trees. Cornell University Agriculture Experiment Station bulletin 415.
Ingels, C. and P. Geisel. 2014. Fruit and Nut Tree Pruning Guidelines for Arborists. University of California Agriculture and Natural Resources publication 8502. http://anrcatalog.ucanr.edu
Saure, M.C. 1987. Summer pruning effect in apple—a review. Scientia Horticulture 30: 253-282
Over the last couple of months I started a series on raised bed gardens, focusing on materials and preparation. In this final installment, I’ll focus on maintenance activities to avoid in your raised bed systems and remind you of three things you should always do.
We’ll start with some practices that damage soil structure and function (GP John Porter discussed this in much detail a few years ago). Tilling, once the mainstay of soil preparation for crops, is increasingly found to cause more damage than good. Grinding the soil into a material with the texture of coffee grounds might look pretty, but it’s devoid of the ped structure that allows water and gas to move through easily. It also increases microbial activity by bringing up microbial spores, which release carbon dioxide to the atmosphere as they digest whatever organic material is there. And tilling will increase the likelihood of erosion and compaction.
This is the opposite of what gardeners should want: an
optimal soil has natural structure which might look messy but allows for good
drainage. It’s also more resistant to compaction and erosion, especially when
it’s protected with mulch (more on this later).
Speaking of drainage, don’t be tempted to add gravel or
some other coarse material at the bottom of the bed. The change in soil texture
creates a perched water table, which makes for a soggy planting bed and optimal
conditions for soil-borne diseases.
While we’re talking about unnecessary or harmful additions to your raised beds, let’s not forget the annual addition of compost or other rich organic material. This is a holdover from old agricultural practices and is not warranted unless you have an organic material deficiency. Without a soil test, you don’t have a clue about what your soil has or what it needs. The problems associated with routine amendments are discussed in this peer-reviewed fact sheet, and are exacerbated by the tillage that is often the means to incorporate compost. Likewise, don’t add fertilizers and pesticides unless you have conclusively identified nutrient deficiencies or pest issues.
The last tradition I’d like to see shelved is growing cover crops. This practice originated in the management of agricultural fields, which were otherwise left bare after harvest. Outside of producing some kale or other winter vegetables, what’s the point of planting a cover crop in your garden, when you can protect the soil in other ways? Cover crops require water and nutrients, which eventually will need to be pulled or incorporated. You are forcing your soil system to continue to support plant growth and be subjected to disturbance with the planting and harvesting of the cover crop. Why not let the soil rest over the winter with a nice blanket of mulch? Give it a chance to regenerate its nutrient load while being protected from unnecessary disturbance.
Two of these tips have been discussed many times in this forum, so I’ll direct you to longer discussions of soil testing and mulching. Mulching is not just important for protecting the soil bed after the growing season, but should be used on actively producing beds. A deep, coarse organic mulch will promote water and air movement, moderate soil temperatures, reduce weeds, and provide a slow feed of nutrients throughout the season. You’ll have to wait until your seeds are up to apply it, of course, but try to avoid bare soil as much as possible.
Soil testing is really crucial for any garden, but
perhaps most important in vegetable gardens where harvesting may decrease key
nutrients over time. It will also guide you in identifying potential heavy
metal problems. The money you will save in not buying unnecessary fertilizers
and other amendments will pay for many soil tests.
Sometimes you will need to add material to your existing
beds if you are not using a natural soil. Soilless media (deceptively
marketed as “potting soil” though no soil is to be found) will decompose and
settle over time, leaving you with a sunken soil system. You will need to add
more of the same sort of media to the beds, making sure you mix it in
thoroughly to prevent a perched water table. (This is why you might consider
using a natural soil and avoiding this annual chore – because a natural soil
will not subside over time.)