Tiny plants that pack a flavor and nutrition punch: getting in on the microgreen trend

If you do any searching for gardening (or even think about the color green), you’re likely bombarded with adds on social media and search engines about all stuff gardening.  One of the recent trends is microgreen production.  There’s all kinds of fancy little systems and gizmos that will help you grow microgreens for a price.  But what are microgreens?  Are they the same thing as sprouts? And do they have the same food safety issues as sprouts?  Let’s discuss, shall we?

What are microgreens?

Microgreens are basically tiny plants harvested shortly after germination.  Unlike sprouts, like the common alfalfa or bean variety, these baby plants are grown on a medium of some sort and just the “above ground” portion of the plant is harvested.  Sprouts, on the other hand, are typically grown in a moist environment without a medium and harvested whole -roots, seed, and all.  It is this wet and warm environment that make sprouts especially risky for food borne illness. 

Microgreens can be any number of different crops, but common types are kale, mustard, chard, broccoli, arugula, and radish.  Sunflower and pea are also common, but they fall more in the “shoot” classification since they are harvested a bit larger.  There’s lots of other crops that are used for microgreens, including herbs like cilantro and even marigolds, so the sky is the limit!

Why microgreens?

There are a few things that make them attractive to farmers which also are good for home growers.  First, it only takes 1-3 weeks for a finished crop.  This fast turn-around makes it easy to keep up with production needs for customers (or your own uses) and also reduces risk.  If a crop fails, it is much less damaging if it only took a week to grow rather than a whole field full of peppers that have been growing for months getting wiped out by disease or a storm. 

Second, is the value and profit.  While there is some investment in seed starting equipment and then continued expenses of seeds, trays, and media, microgreens have a high per pound value.  Microgreens are used in small quantities and are therefore sold in small quantities.  A small amount you may purchase at a farmers market for a few bucks may be an ounce or less.  When you calculate it out by the pound, microgreens are sold for between $20 and $200ish per pound (depending on the variety, organic production, other factors). 

And of course, microgreens lend themselves to year-round production.  It can be a fun and easy way to get some flavor and color on the plate even in the dead of winter.  Just a few square feet of production area can provide a decent sized crop, so it is great for those with limited space or no garden at all.

Look ma….I made fancy mac and cheese. All I had to do was add some microgreens.

Microgreens are popular with home cooks and chefs alike because they pack a flavor punch and add some color and texture with just a pinch or two of product.  Studies have shown that microgreens also pack a nutritional punch in a small package.  However, production practices can greatly influence nutrient content, especially light.  Microgreens grown with higher quantities (brightness) and quality (spectrum colors, mainly red and blue but also green) of light have higher nutrient values. 

How do you grow microgreens?

The way you grow microgreens lends itself to why they are so popular to grow, for both home enthusiasts and farmers alike.  Microgreens are basically recently germinated seedlings.  If you are good at seed starting, you can be good at growing microgreens.  Lots of the ads I’ve been seeing recently are for attractive but pricey growing trays and mats that you just lay down and water.  However, budget conscious gardeners can grow them pretty simply and inexpensively at home.  And you probably have most of the equipment you need, especially if you start your own seeds each year! 

Microgreens are usually grown in those flat plastic seedling trays, the type that don’t have cells in them (the ones used to hold the cell packs).  For those “in the know,” they’re called 1020 trays.  You can either use a sterile media like peat or coir or purchase specific fiber mats (I have some made from hemp -they work well but smell like a moldy gym sock full of weed when in use). We’ll talk about the importance of a sterile media when we talk food safety. 

A demonstration of sowing microgreen seeds on hemp fiber mats.

The sowing density of seeds can vary by crop due to seed and seedling size.  Typically, one ounce of seeds can sow anywhere from one to eight 1020 trays.  In general terms, large seeded crops like chard and beets may take up to ½ cup per tray and small seeded crops like radish or kale might require ¼ cup.  Tiny seeded crops, like sorrel may need just a few tablespoons.  If you’re really into production, Penn State extension has an excellent Excel calculator to calculate seeding rates. Typically, you’ll broadcast the seeds on top of your media and then maybe sprinkle a little more media on top to make it easy (no dibbler here!).

Most seeds require darkness to germinate, as well as high humidity.  You can use humidity domes and cover trays with an opaque material to achieve this, or you can use the trick that producers use and stack trays on top of each other for a day or two.  This keeps the seeds covered and dark and preserves moisture and humidity.  Just unstack them after a day or two and stick them in their growing location.  As with seed starting, you’ll have the most success if you provide some good quality light and heat.  (You can search through old articles to find lots of info on seeds starting).  There’s research that shows that light is a big factor in microgreen growth, coloration, and nutrition levels. 

You’ll harvest your microgreens typically one two three weeks after sowing.  Typically, this is done after at least one set of true leaves have formed, but you can usually let them go until there are at least two (or sometimes three) sets of leaves.  To harvest, use a sharp, cleaned pair of scissors to snip the seedling off just about soil level, being sure not to disturb the media so that you don’t get it on your precious produce.

There should be no need to wash the microgreens right after harvest and before storage, since they’re typically grown in a clean environment.  Washing before storage can increase storage moisture to levels that support microbial growth, reducing storage time and also increasing the risk of human pathogens.  Instead, store microgreens (and most leafy greens) without washing and wash just before use. 

Working with a local farmer to demonstrate microgreen production at a regional production conference.

Food Safety

As we learned when discussing what microgreens are and comparing them to sprouts, we learned that microgreens have been found to have much lower risk of human pathogens.  However, the risk is not zero, especially if production practices are conducive to pathogens.  We just discussed that washing prior to storage can lead to microorganism contamination, but there are a few other areas where contamination is easy.  To reduce contamination, follow these steps:

  • Always use clean and sanitized trays or containers.  If reusing trays, be sure to wash with soapy water then sanitize with a dilute bleach solution or other approved sanitizer. 
  • Keep the production area clean and sanitized.  Microgreens are often produced on multi-leveled vertical racks, so contaminants can drip down.  Make sure all surrounding surfaces are clean.
  • Use sterile media for production.  This is typically a soil-less media made primarily of peat or coir, like a seed starting mix, or specialized fiber growing mats.  Do not use regular potting soil, any mix containing compost, or anything containing soil to avoid the introduction of human pathogens or other microorganisms that might affect the crop, such as those that cause damping off.
  • Use cleaned and sterilized seed. Many companies sell seeds specifically for microgreens that have been processed to remove pathogens.  I’ve seen seed production, and while it isn’t filthy, it typically isn’t sterilized to the level of food production standards.  You can sterilize common seed at home using a solution of hydrogen peroxide or vinegar.  For guidance, visit this guide from K-State extension.
  • Use a clean source of potable drinking water.  If you wouldn’t drink it as is, don’t use it.  Typically this means it should be straight from the tap of a trusted source. 

Conclusion

Growing microgreens can be a fairly easy and enjoyable way to produce something fresh and green year round.  In terms of production practices, it is basically ramped up seed starting where your seedlings only grow a few weeks before harvest. This makes it a fairly easy process and one that can be done almost anywhere.  If you’re looking for an indoor gardening project or just want to add a quick source of nutrients to your diet, give microgreen production a try. 

Sources and resources:

Microgreen nutrition, food safety, and shelf life: A review

Microgreens and Produce Safety

Microgreens—A review of food safety considerations along the farm to fork continuum

A step-by-step guide for growing microgreens at home

Pruning Paints Debunked

When my turn comes up to blog for the Garden Professor site I like to reflect on the horticulture in my own gardens and orchard. Right now I am focused on pruning my old apple and stone fruit orchard. It has suffered bear attacks, drought, and mismanagement before we arrived in 2018. The previous owners were very aware of the need to treat pruning cuts large and small. The remnants of tree wound dressings are found all through our orchard and range from white latex paint to silicone caulk. Unfortunately there has never been good research evidence to support pruning paint use. Despite the lack of any published evidence, for their usefulness, pruning paints are still available in garden centers and there are no end of do it yourself preparations that gardeners continue to use on pruning wounds.

Wound dressings did not protect this apple branch from decay fungi

So why paint the cuts on your fruit trees after pruning? One idea is to keep the surface protected from infection by pathogens. Plant pathogenic fungi and bacteria can cause disease that may lead to blight, cankers, or wood decay.

Laetiporus gilbersonii (chicken of the woods) is a common brown rot wood decay fungus that destroys cellulose in wood.

Wounds are often implicated in pathogenesis or disease development. Many horticulturists believed that wound dressings provide a barrier to entry of pathogens and insects. Fruit trees are easily decayed by a number of fungi which cause white and brown rots in their wood. Wood decay organisms enter through wounds created when branches break from excessive fruit loads or when pruning wounds expose heartwood or significant amounts of sapwood. So painting cuts became a very common practice advocated by gardening columns and various books over the last century.

Wound dressings used in Ukraine for many years on this shade trees did not stop decay fungi from fruiting under the wound dressing! Photo courtesy Igor Signer, Kiev, Ukraine

Wood contains cells that store starch. Here, parenchyma cells in the wood ray tissues have been stained purple to show their starch content. Fungi that invade wood use this stored energy to grow, invade and degrade wood. Fungi invade both the heartwood (non-living) and the living, water transporting sapwood. Sap-rotters typically lead to the decline in tree vigor and canopy density.

Over one hundred years ago Howe (1915) recognized that pruning paints did not help wounds to close, in fact, they retarded the development of callus wood especially in peaches. Howe called into question the necessity of using wound dressings at all. Still the use of wound dressings has prevailed to this day.

Shigo and Shortle (1981) showed that wound dressings do not prevent decay nor do they promote wound closure. If the poor pruning practices that harm trees are abandoned, then wound dressings are unnecessary (never mind that they don’t work). Shigo often maintained that tree genetics determine the extent of decay forming in a given species. His work conclusively showed that flush cuts would lead to more decay than cuts that were made outside the branch collar or bark ridge.

Expanding foam? As far as I know there is no research on expanding foam but lots of anecdotes and observations of how it is often used to fill tree cavities. Filling cavities with cement to prevent or limit decay is a practice that subsided some decades ago and is generally not recommended as part of modern arboricultural practice. By the time decay has caused a cavity it is usually well entrenched in the wood of a tree and is not controlled by filling in the void. The best way to limit decay in trees is to prune them frequently so cuts are never large and the tree (fruit or shade) develops a strong structure that is unlikely to fail.

Literature:

Chalker-Scott, L., and A.J. Downer 2018. Garden Myth Busting for Extension Educators: Reviewing the Literature on Landscape Tree. Journal of the NACCA 11:(2) https://www.nacaa.com/journal/index.php?jid=885

Howe, G.H. 1915. Effect of various dressings on pruning wounds of fruit trees. New York Agricultural Experiment Station, Geneva, N.Y. Bulletin No 396.

Shigo, A.L and W. C Shortle. 1983. Wound dressings: Results of studies over 13 ykears. J. or Arboriculture 9(10): 317-329.

Shigo, A.L. 1984. Tree Decay and Pruning. Arboricultural J. 8:1-12.

The complicated issue of heavy metals in residential soils. Part 3: How can we garden safely in the presence of heavy metals?

This is the last part of our discussion on gardening in soils that contain heavy metals (you can catch up on part 1 and part 2 if you need to). Today we’ll focus on the strategies you can use in your gardens and landscapes to reduce your exposure to soil-borne heavy metals.

Raised beds can be an easy solution for gardeners with contaminated soils

Test your soil!

First – and this should really go without saying – you must test your soil to determine if it contains heavy metals of concern. The COVID19 pandemic provides the perfect comparison: you can’t assume you don’t have the virus just because you don’t have symptoms, and you can’t assume your soil doesn’t have toxic heavy metals just because you don’t think it does. The only way to know for sure, in either case, is through testing.

This eyesore did more than spoil the view.

Most soil tests routinely report aluminum, lead, zinc, and aluminum. Other metals, such as arsenic, cadmium, and chromium, may not be part of a basic soil test and you will need to request additional tests if these metals are likely to be present. Often, county health offices will provide free soil testing if you live in a region where there are known contaminants. For example, I live in the Tacoma area where large amounts of arsenic were deposited for decades downwind of an aluminum smelter. Residents of Pierce County can get free soil testing because of the potential danger.

The aluminum is higher than we would like to see, though everything else looks fine.

Even if you don’t live in an area where industrial or agricultural activity may have added toxic heavy metals to your soils, your soil may naturally contain high levels of some metal of concern. As I’ve mentioned in a previous post, our soils have high levels of aluminum. Because we are not downwind of the smelter site mentioned above, I would not have assumed we had any metals of concern, given the rural location of our land, but knowing this informs my choice of vegetables to plant.

The demolition of the Tacoma smelter. Finally.

Avoid adding more heavy metals

Fortunately, many of the consumer products that contained heavy metals are now gone and no longer will add to existing levels of soil metals. But there are still sources out there that gardeners are well-advised to avoid.

  • Older treated timbers. As mentioned in my first post, landscape timbers were once treated with a chemical preservative containing arsenic and chromium. Even though gardeners love reusing materials (we are a thrifty bunch!), these older timbers should be removed if they are still on your property. New timbers are treated with a copper-based solution, which is a more environmentally friendly preservative.
  • Kelp-based fertilizers and amendments. While these products are wildly popular with gardeners, they aren’t very effective fertilizers. Moreover, some kelp species accumulate heavy metals, like arsenic, in seawater and these metals will become a permanent part of your soils. Take a look at this fact sheet for more information.
  • Recycled rubber mulch. This product should be avoided for many reasons (you can read more about the problems in this fact sheet). As it disintegrates it releases high levels of zinc into the soil. And while zinc is an essential micronutrient in plants (and people!), high levels are toxic.
  • Unregulated composts and organic products. Certified composts and other organic products have been tested for pesticide residues and heavy metals: unregulated products have not. Unless you are making your own compost from materials you know to be free from contamination, your safest bet is to purchase certified products.

If you have materials like old timbers, you should never burn them or throw them away. They need to be disposed of as a hazardous waste, much like old cans of paint, mercury-containing thermometers, etc. Eventually, we may be able to use these hazardous discards for biofuel production through pyrolysis, or extract the heavy metals from them for reuse. For now, just dispose of them in a legal and environmentally responsible way.

Cedar is naturally decay-resistant and can be a good choice for rasied beds

Suggestions for safe gardening

If soil testing reveals high levels of metals of concern, there are work-arounds to allow you to still enjoy growing vegetables safely. If your soil tests reveal that your soil is safe for growing edibles, congratulations! You may still benefit from some of the suggestions below.

  • Cover exposed soil with ground covers and mulches (coarse organic or inorganic materials) to eliminate metal-laden dust.
  • Create raised beds for edibles using untreated wood or other metal-free materials. Line the bottom of the bed with an impermeable membrane to prevent movement of soil-borne metals into the beds.
  • If raised beds are not possible, use large containers to grow edibles.
  • Avoid using galvanized tubs, as they will leach zinc (and sometimes chromium) into the soil.
  • Fill beds and containers with clean (i.e., tested) soils or potting media.
  • Don’t plant vegetables near roadways, which are a source of airborne lead.

Planning Ahead (in a pandemic) for Vegetable Garden Success

Looking back to January 2020, most of us would have never imagined the year we’ve had.  All of our best laid plans went away and instead we socially distanced, scavenged for toilet paper, and canceled events and vacations.  But one thing that wasn’t canceled was gardening.  By June, garden retail sales had increased 8.79% over the average, a big jump for a trend that was already showing increased gardening over the last few years.  Wanting to grow food to ensure a safe food supply was one reason gardening increased this year, but it also served as away for people break the boredom of being stuck at home. 

One bit of advice that we in Extension always give to gardeners, young and old, is to plan ahead, especially if they are growing fruits and vegetables or starting their own seeds.  Given that rapid increase in garden sales, many would-be gardeners were frustrated to find the seed racks and plant shelves empty and online catalog retailers out of stock. From personal experience, I can tell you that white beets don’t look quite as pretty in the jar as those bright red ones.  Given the fact that the pandemic is likely to continue well into 2021, it would be a good idea for those thinking about gardening to plan ahead on what they want to grow and plan to buy seeds and supplies early.  This not only helps you plan out what you want to grow and when to start or plant it, but will also help you beat the rush and get the plants or varieties that you want. 

Here are some things to consider while planning for your vegetable (or other) garden:

  1. What are your garden goals?  Are you wanting to harvest for fresh eating only? Hoping to preserve harvest for later?  Have extra to sell or give away?  Figuring out what you hope to accomplish will help you plan out how to use your space most effectively.  Plan to plant extra of stuff you plan to preserve or give away, and plant it all at the same time to have a larger harvest.  If you’re focusing on fresh eating for just your family, planting smaller quantities of each plant and spacing them out over time would be better.
  2. What do you enjoy eating or growing?  Focus on the crops that you and your family like to eat, especially if you have limited garden space or time. 
  3. What resources are you willing to commit to gardening?  How much money do you have to invest in seeds, plants, or supplies?  And how much time do you have to spend per week?  You should base your garden size on what you can reasonably support.  And also look for investing in efficiencies.  For example, adding drip irrigation will be an investment of time and money up front, but will save on water bills and time spent watering the garden and will likely increase your harvests so it can have a pretty decent return on that initial investment.
  4. Are you planning on growing throughout the garden season?  Many people focus on gardening May through September and often miss those very productive early spring and fall months when cool season crops flourish.  Making a plan for using space effectively can include growing an early season, summer, and late season crop all in the same spot using interplanting or succession planting.  If you aren’t sure what to grow when in your climate, look for local growing guides or calendars to help.  Your local Extension office will likely have some good resources to share.  Having an idea what you want to grow throughout the season will also help you make early purchases to ensure you have what you need throughout the season.  Seeds are usually off the store shelves by mid to late summer, so buy seeds in the spring for those fall and late planted crops just to be prepared. 
  5. Are there things you want to grow that would be easier to buy?  This question is especially important if you have limited space, time, or money.  Crops like potatoes, cabbage, and onions are often cheaper for home growers to buy than grow and crops like squash can take up a lot of room and are often easy to buy (there’s usually plenty of zucchini everywhere in the summer).  Focus on those things you can’t buy like interesting varieties of tomatoes, peppers, etc.
  6. Are you ready to deal with diseases and pests throughout the garden season?  Be ready to scout the garden for pests and do a little research on the common pests and diseases on the crops you’re growing so you know what to look for.  You can often reduce the likelihood of pests and diseases by growing newer resistant cultivars versus older varieties and heirlooms that don’t have resistance bred in. 
  7. What has worked (or not worked) for you in the past?  Focus on growing those things you do well.  Take some time to research or learn how to better grow the things you haven’t grown so well in the past (extension resources are great for this- contact your local office or search for info online, looking for pages that end in .edu).  And don’t be afraid to try something new – you can find new favorites by trying out new cultivars or even new crops. 

Using some of these steps can help you plan ahead for a year of garden success. The key is to start early, and especially in 2021, buy those seeds and supplies early.  When you do, take a look at your plans for the whole garden season and plan accordingly in advance.  Though while you’re out there buying those seeds, be sure to leave a packet or two on the rack for me.  I’d prefer to have red beets for pickling this year instead of those white and yellow ones. 

The complicated issue of heavy metals in residential soils, part 2: How plant species and environmental variables complicate the issue

Last month we discussed the various heavy metals that might end up in your garden and landscape soils. Today we’ll consider how different factors can alter heavy metal uptake by plants.

Parking strips can contain high levels of lead after decades of car exhaust

First of all, let’s consider plant uptake. Plant roots can either accumulate a particular metal or exclude it. If they exclude it, that’s the end of the story, (though it’s still a soil contaminant). If plants take it up, they can either store it in their roots, or they can transport it to some other part of the plant – stems, leaves, flowers, and fruits are possible destinations for metals in accumulator plants. Accumulation varies with plant species and life stage; in other words, seedlings may have different uptake abilities than later life stages. And of course, whether a plant accumulates or excludes a particular heavy metal does not mean the same uptake pattern holds for other heavy metals.

Clay soil will bind heavy metals tightly

Secondly, soil conditions will influence heavy metal mobility. Heavy metals are positively charged, so anything in the soil that carries a negative charge – like clay particles and organic matter – will tend to hold heavy metals in place. That can either be good or bad, depending on your use of the landscape. If you are growing edibles, metals that are tightly bound to the soil are less likely to be taken up. But this also means that they are pretty much there to stay. Sandy soils don’t hold metals well, since sand particles carry no charge, so heavy metals are free to move elsewhere – into the air, into bodies of water, or into plant roots.

How soil variables affect heavy metal uptake

Additions of fertilizers, like those that contain phosphate or that chelate metals, will also increase the ability of plants to take up heavy metals. Likewise, earthworms ingest metals and bind them to other compounds that can be taken up by plant roots. And microbes associated with the roots (and the roots themselves) can acidify the rhizosphere, solubilizing metals and making them easy to incorporate.

Earthworms make all kinds of things available to plants – including heavy metals

It’s apparent that many factors are at play in determining whether plants will take up heavy metals, thus making it impossible to come up with lists of “safe” plants. There are hundreds, if not thousands, of studies on heavy metal uptake of vegetable and other crop plants worldwide, and the variability among their results is a direct reflection of the complexity of soil environments and plant physiology. Nevertheless, there are some very general observations about accumulator species that can be gleaned from the research:

  1. Roots are the most likely tissue to contain heavy metals, since they are the point of uptake; arsenic can accumulate in carrots and lead has been found in carrots and potatoes;
  2. Stems are much less likely to accumulate heavy metals, as they are basically just a straw connecting roots to leaves and other terminal tissues;
  3. Leaves, including basil, lettuce, and spinach, can accumulate heavy metals. Moreover, it appears that red leafed cultivars may accumulate more than those that are green leafed;
  4. Flowers and fruits, including vegetable tissues that produce seeds, are less likely to accumulate heavy metals. For plants that depend on animals to spread their seeds by ingesting the surrounding fruits and then excreting their seeds, it would be an evolutionary disadvantage to have those tissues carrying toxic heavy metals. That being said, there are vegetables, like beans, broccoli, and zucchini, that can accumulate heavy metals such as lead and arsenic.
Red leaves may contain more heavy metals than green ones.

By this point, I think we can agree there will never be a “one size fits all” approach to gardening safely when heavy metals are part of the soil, water, or air environment. Next month I’ll provide suggestions on how to navigate the confusion and design your own approach to creating gardens and landscapes that work around heavy metal contamination.

The worms crawl in and the worms crawl out but these worms kill your plants

Our first major frost hit my part of Arizona a month ago, killing all tomato vines. I did my thanksgiving cleanup chores–removed all the vines and ground them into mulch. I noticed an ominous symptom on one a few of the heirloom varieties (Prudence Purple) that I removed—galled roots. This symptom when seen on tomato is evidence of Root Knot Nematode (RKN). More about RKN shortly. Nematodes are non-segmented worms, mostly free living in soil and feed on bacteria, fungi, small animals or each other. Nematodes are small, barely perceived without magnification but easily observed under low power microscopy. Most nematodes are principal components of the soil food web and are vital to its health and functioning. A few kinds (>30) are opportunistic plant feeders. Plant pathologists consider nematodes plant pathogens because they evoke complicated responses in plant physiology leading to the development of symptoms.

Root knot nematode (Meloidogyne spp.) forms extensive galls on Prudence Purple tomato by the end of a growing season.

Plant parasitic nematodes have some common features and some rather diverse feeding habits and lifestyles. All plant parasitic nematodes have a stylet or spear at their mouth end that is used to puncture plant tissues and such the sap from their host. Looking under a dissecting microscope you may not be able to identify the genus of a nematode but you can tell if it is bad for plants by seeing the spear just behind its mouth. Plant Parasitic Nematodes (PPN) are either migratory or sedentary. All PPN reproduce by eggs and molt once inside the egg emerging as a second instar juvenile nematode. After a couple more molts the juveniles become adults. Male nematodes are less common than female worms. As adults they can keep feeding from plant to plant if they are ectoparasitic (feeding outside of the root) or they can settle down and make eggs inside a cyst or gall. Some nematodes are endoparasitic and once inside the root never leave it until their eggs hatch and juveniles swim off find another host.

Even though these marigolds are heavily galled by root rot nematode their only above ground symptoms are dwarfing or slowed growth

Gardeners should be on the lookout for PPN by noticing symptoms of infection. The most common symptom caused by nematodes is stunting or reduced growth. There may be no other symptoms observable. When the number of PPN is quite large, yellowing or chlorosis can occur as the worms shut down a plant’s ability to take up water and minerals. RKN is the most common destructive plant parasitic nematodes for many gardeners. The gall symptoms on roots are indicative of an infested host. Galling can be light or complete, occurring on every root the plant has. RKN survives in soil for years even without a host because the eggs enter a dormant stage called cryptobiosis. Hatch is snychronous with susceptible roots that grow nearby. Root knot nematodes can build huge populations in a single growing season. Gardeners get nematodes by introducing contaminated soils that come with plants to their gardens. Since symptoms don’t show on plants with minor infections, people think they are buying healthy stock. Even with RKN, there may be juveniles in the soil that have not formed galls yet and when introduced to your garden they will develop later on susceptible plants.

RKN has a very wide host range. Fruit trees, impatiens, calendulas, and tomatoes are a few of its common hosts. Perennial plants can really develop high populations of RKN because the host is undisturbed and provides many seasons for the pathogen to develop. Once detected as galls on roots the plant should be removed and destroyed. RKN is particularly horrible for tomatoes and other annuals when it combines with fungi that also cause disease. RKN forms disease complexes with Fusarium which causes wilts. When tomatoes are infected with both RKN and Fusarium the symptoms are severe, and the plant will die relatively early in its life cycle often before a crop can develop.

Chipping or grinding and composting will kill most nematodes if you want to reuse your greenwaste. More likely RKN will survive as eggs in the soil. Soil samples that find just one RKN per gram of soil sample are considered hazardous as the worms can rapidly develop from these low populations. You may have heard that Marigolds will control RKN. Switching gardens to a non-host (crop rotation) does help decrease populations. And French marigolds and crucifers if tilled into soil as “green manure” will decrease RKN but these methods will not eliminate them from soil. There is a dose response to tilling in mustards so the more you incorporate the more RKN will be harmed. Some varieties are better than others. Fumigation provides a good level of control but is not feasible outside commercial agriculture. Soil solaraization with plastic tarps also controls nematodes in the upper regions of soil but there are usually many eggs that survive in lower soil profiles. The best control is not to plant susceptible plants.

Some tomato varieties are resistant to RKN. In fact VFN (Verticillium Fusarium and Nematode resistant) varieties should be chosen to avoid recurrent problems. The resistance to RKN in tomato is not complete and under high nematode populations and/or high temperatures the resistance can break down and even resistant varieties can develop galls and symptoms. There are no pesticides that home gardeners can use to kill nematodes. However there are biological controls of nematodes and since they are soil food web opportunists, increasing the diversity of organisms in soil tends to cut down on PPN. As always, fresh arborist chips applied as mulch will build a resilient soil food web and will slow the development of PPN harmful to garden plants.

Hydroponics for the Holidays? Home Systems are a hot holiday gift list item

Systems to grow fresh produce in your home using hydroponics or other automatic processes have been popular for several years but seem to be even more popular this year with more folks home and looking for something to do and hoping to produce their own food.  As a result, these systems are popping up on holiday wish lists and gift buying guides all over the internet.  But are they worth it?  And if so, what should you look for in a system? 

First off, what are these systems? And what is hydroponics?  Hydroponics is the process of growing plants without soil in a aqueous nutrient solution.  Basically, you provide all the nutritional needs of the plants through nutrient fertilizers dissolved in water.  These systems can grow plants faster and in a smaller space than traditional soil-based production. It also allows you to grow plants indoors and in areas where you would not normally be able to grow.

This Aerogarden (which is the previous generation) has a digital brain that controls light and water schedules for the specific growth phase of the plant and yells at you when it thinks you need to add more fertilizer solution.

As for systems, you might have seen what is probably the “oldest” one on the market – the AeroGarden.  Since it is the oldest and most common, that’s the example we’ll be staying with.  It has been around a few decades and has evolved from a basic electronic system to fully automatic, “smart”Bluetooth connected systems that you can control with your phone.  In recent years there have been many new systems come onto the market at all different sizes and price points.  A quick search of online retailers will usually provide an array of options – from DIY kits to plug-and-play enclosed systems such as “Click & Grow” and “Gardyn”. My only experience is with the Aerogarden system, so I can’t speak to any of the others (though I’d love to try them out!).

The answer to “are they worth it” is up to you, really.  Most home based hydroponic or aeroponic systems offer convenience, but at a cost.  Most cost several hundred dollars and are small, so they produce a small amount of produce (or other plants) at any one time. So you have to determine what goals you, or your intended giftee, have with the system. 

“Baby” lettuce, 18 days after sowing. The current version of this 9-plant Aerogarden system, called the “Bounty”, retails for $300 but you can usually get it for under $200 on sale.

The benefit of the “plug-and-play” enclosed systems like the AeroGarden is that basically you can take it out of the box, set it up in less than 10 minutes, and have some fresh lettuce or herbs in a few weeks.  It controls the water cycles, lighting, and all other conditions for growth.  You just drop in pods that contain the seeds suspended in a spongy-material.  The smallest system, that holds 3 plants, retails for $100.  As an additional expense comes from buying refill kits to replant. The mid-size systems are the most common and range from $150-$300.  The largest system, the “XL Farm” retails for $600. But these systems are commonly on sale at pretty significant discounts. 

For many systems, you typically buy a new set of pods (there are different plant variety selections), but there are pods you can buy to assemble your own using your own seeds.  For the AeroGarden, the pod kits range from $15 up to $30 to grow up to 9 individual plants. There are other plug-and-play systems on the market, as well as some kits that are more build-your-own and less automated. 

No matter which systems you buy (or gift), keeping these costs in mind is important.  If you’re looking for a fun and easy activity with the benefit of a little fresh produce and aren’t as concerned with production costs these systems may be for you – and if you are giving or getting them as a gift that definitely makes it more economical. But given the cost of the plug-and-play systems and the refill pods, they will never be an “economical” option for producing your own food.  If you are wanting to produce food on a budget and you’re interested in home hydroponics, look for plans to build your own or buy a DIY kit. 

The complicated issue of heavy metals in residential soils, part 1: What are toxic heavy metals, and where do they come from?

The popularity of home gardens is exploding as we wait out the COVID pandemic

So many of us are growing our own vegetables – either as experienced home gardeners or as COVID19-isolated novices. There is a lot of effort in figuring out garden beds, vegetable choices, and growing medium – but one of the issues rarely considered is whether there are heavy metals present in the local soil and/or growing medium. We can’t see heavy metals, or smell them, so we need to have a way of assessing their presence before we plant edibles.

In the next few months, I’ll tackle the complicated science behind this invisible threat. Today, let’s look at the heavy metals that are commonly found in garden soils and where they might come from.

What heavy metals do gardeners need to monitor in their soils?

Heavy metals are exactly that – they are dense elements that have certain chemical properties that define them as metals. In fact, most known elements are considered to be heavy metals. Fortunately, there are only a handful of heavy metals that are commonly found in residential soils. Some of these heavy metals are necessary for life – iron, manganese, and zinc, for example – but others have no known biological function. Arsenic and lead, for instance, can interfere with enzymatic activity and effectively poison biochemical pathways. There is no “safe” level of heavy metals that are not essential nutrients.

Here’s a table of the most common toxic heavy metals that might be found in your soil, and possible anthropogenic sources:

Heavy metal Sources of contamination
Aluminum* Smelting
Arsenic Pesticides, smelting, treated timbers (old)
Cadmium Paint
Chromium Fly ash, metals industry, paint, leather tanning, treated timbers (old)
Lead Gasoline (leaded), paint, pesticides, plumbing, smelting, solder
Nickel Plumbing, smelting

*Aluminum is a light metal, not a heavy metal, but has similar biochemical poisoning activity as toxic heavy metals

Some of these sources of contamination are not relevant to where I live – why do I need to test my soil?

Gardeners may be tempted to look at the chart above and feel relieved, because pesticides and paint no longer contain heavy metals, they don’t use old treated timbers, and they know that leaded gasoline is a thing of the past. What many don’t consider, however, is that heavy metals are elemental – they don’t break down, though they may change their chemical form. They are a permanent part of soil chemistry unless they are removed by physical or biological means.

The underlying soil in housing developments built on old agricultural land often contains high levels of arsenic – because that was the active ingredient in pesticides many decades ago. If the topsoil was removed during construction, it may have been taken to a commercial soil facility where it would have been used to create landscape fill mixes for new landscapes elsewhere. The same is true for land near older roadways where lead from gasoline was released from vehicles over many decades. Not only are lead, arsenic, and other heavy metals in the soil, they also end up in the air when soil is disturbed by erosion or tilling.

Nearly all soils contain some level of some heavy metals. They are naturally occurring, after all, so their presence is not necessarily from anthropogenic activities. Regardless of the source, it’s important to know whether any of these harmful elements are in your garden soils, especially if you are growing edibles. A soil test is the only way to find out.

Here is a soil test of my own raised bed system. While my nutrient levels are optimum, and lead is very low, the aluminum level is quite high. What should I do?

Why aren’t there guidelines on heavy metal uptake in vegetable gardens?

It would be ideal if there was a list of “safe” and “dangerous” vegetables to plant when heavy metals are present. Unfortunately, real life rarely fits into lists and there are numerous sources of variability. Next month I’ll discuss the complications that arise when we consider plant species, heavy metals, and environmental variables.

Fall is for fungal fruit

Summer is done. The last apples are coming off my orchard trees now and persimmons are ripening fast. Some fruit remains to be picked but most is off. As garden productivity subsides we turn our tasks to winter. In Southern California it means planting the winter vegetable garden, in Northern Mn snow has already flown so gardens are shut down now. For fungi that may be pathogens in our gardens, it is a time for reproduction. Fall is the time for fruiting and for gardeners a time to reckon with next year’s disease cycles.

Most fungi are saprophytic, that is they live on dead or decayed organic matter. Fungi are largely responsible for recycling forest nutrients from litterfall (leaves, branches and whole trees) back to soil minerals. Without fungal decay, mulch would never break down and organic matter would pile up. If you use fresh wood chips (often advocated in this group) you may notice that after some time they are full of fungal mycelium or cordons (rhizomorphs). This is normal and healthy—a good sign that your mulch is decomposing and improving the underlying layers of soil.

Furngi survive as fruting bodies in cankered branches, dead wood and leaves

Some plant pathogen fruiting bodies are edible. The mushrooms formed by Armillaria are often collected and considered delectable by many. Most edible fungi are saprophytes or mycorrhizal fungi. Truffles and other edible mushrooms like Chanterelles are plant symbionts often benefiting oaks and other northern temperate trees. Some wood decay fungi are also considered a delicacy such as the Oyster mushrooms (Pleurotis spp.) or the sulfur mushroom (Laetiporus gilbersonii). I don’t recommend harvesting wild mushrooms for food unless you are able to accurately identify what you collect, even then, second opinions of mycologists are a good idea. Also, not everyone reacts the same to fungi when they consume non-commercial mushrooms, so moderation is best or just get your fungus from commercial sources.

The sulfur conk (Laetiporus gilbersonii) is an edible wood decay mushroom

Not all fungi are beneficial. Some have evolved life histories that allow them to gain energy not from organic matter or dead plant materials but from living plants. These are parasites. Fungi have been evolving their lifestyles for about 400 million years and in that time have developed several strategies involving plant hosts to live and reproduce. Sixty five million years ago, after the Cretaceous-Paleogene extinction event that famously destroyed dinosaurs, fungi bloomed on earth and increased in importance. As land plants diversified, so did fungi developing many forms and parternships, many of them becoming essential to plants such as mycorrhizae. A few fungi specialized as plant pathogens.

Fungi use their reproductive structures to survive and ready themselves to attack susceptible plants. The most common fungal fruiting body the mushroom may not seem like a survival structure. But mushrooms can produce millions if not over a billion spores. Massive spore production ensures that some of those spores will find a place for the organism to survive. Also some mushrooms found on trees (sometimes called conks or bracket mushrooms) are perennial, and live for years—each year they add a new spore bearing surface over the last one. Many of the pathogenic tree fungi that produce conks fruit in the fall or winter.

Mushrooms help fungi survive by producing millions of spores. Don’t attempt to eat this kind though as it is an Amanita and is poisonous! Never eat wild or collected mushrooms without proper identification and study.

Many fungi form their fruiting bodies as small melanized structures that contain their spores. These are often formed in dead host tissue, such as dead twigs or branches. The spores are protected until they are splashed by water onto tender or susceptible plant tissues such as shoots. In soil, fungi can form hyphae that are very concentrated and melanized in to long lasting structures called scleortia. They lay dormant in soil for years until a susceptible root grows into them. Crop rotation often helps to limit disease but some fungi can last decades between crops and remain viable by producing thick walled spores called chlamydospores or sclerotia. The wilt fungi (Fusarium and Verticillium) survive in this way.

Another key strategy that fungi use is a kind of timing called phenotypic synchronicity. Fungi often have their spores ready to be dispersed exactly when new growth or susceptible plants are available for infection. The timing also often aligns with weather conditions that favor spore dispersal or arrival at the intended plant growth stage or phenotype.

Fungi evolved with land plants to take advantage of the environmental conditions and phenology of their hosts. We can interrupt the process with a bit of diligence as gardeners. As fall continues and winter approaches, it is a good time to remove dead twigs and branches from perennials that are prone to disease, clean up fallen or dead flowers from plants like Camellia that are attacked by petal blight because the flower mummies contain sclerotia that start the disease in the Winter. Unfortunately removing conks from trees does nothing to stem the progress of wood decay fungi in the tree they formed on, or their further spread, because so many spores are formed that the few mushrooms we remove will not stop those diseases. Some evidence suggests that increasing soil organic matter will over time reduce soil-borne pathogens, but once a pathogen has affected a perennial, there is often little to be done about it as in the case of Verticillium wilt of shade trees. No matter how fungi survive, its always a good idea to apply fresh tree trimming chips around perennials in the garden….

Smashing Pumpkin Myths: Bleaching to extend shelf (and porch) life

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Scrolling through social media in September and October and you may see those basic signs of the season: scarves, pumpkin spice lattes, sweaters, and Halloween ideas galore.  One of those Halloween ideas is to extend the life of your pumpkins, carved or otherwise, by giving them a treatment with household bleach.  Keep scrolling and you might see another post decrying the use of bleach as inhumane and poisoning for wildlife.  So which is it?  Is bleach safe to use as a sanitizer on your jack-o’-lantern or are you poisoning the neighborhood squirrels?  Let’s use our gourd to explore the science.

The bleach acts as a sanitizer, neutralizing fungi and bacteria on the surfaces of the pumpkin that will cause decomposition and rot.  Even un-carved pumpkins will eventually succumb to degradation under the right conditions.  But if bleach kills fungi and bacteria, will it kill wildlife? The answer is – not if it is used correctly.  Bleach, and sodium hypochlorite (the active chemical in bleach) are toxic if consumed directly in concentrated amounts, however, dilute solutions break down quickly in the environment.  Products containing sodium hypochlorite, including plain household bleach, are actually approved and labeled for use as a sanitizer by produce farmers to reduce both human pathogens and decomposition microorganisms and extend the shelf life of produce that finds its way to the grocery store, farmers market, and any other avenue from the farmer to the consumer.  These wash water sanitizers are used more for reducing cross contamination of from pathogens introduced to the water from dirty produce, but it can reduce the microorganism load on produce items. If used correctly to sanitize the surface of the pumpkins, bleach DOES NOT pose an increased risk to wildlife (or human) health.

What is the proper way to use bleach in sanitizing that pumpkin so that it doesn’t face an early demise?

  1) Make sure the pumpkin is clean by washing with plain water or a mild detergent to remove any soil or debris.  Sanitizers like bleach are quickly neutralized (used up) on dirty surfaces (this is a good lesson for home cleaning, too – you cannot sanitize a dirty surface). 

2) Prepare a DILUTE solution of plain household bleach (unscented, and not “splashless”). The recommended concentration is 200ppm sodium hypochlorite, which you can achieve with 1 Tablespoon of bleach per gallon of water.

3) Apply the solution to the pumpkin using a spray bottle.  Alternatively, you can prepare enough solution to dunk the pumpkin(s) and immerse them in the solution.  If you are sanitizing a carved pumpkin, I would opt for the spray method – dunking may result in infiltration of the solution in to the exposed flesh. It will still break down since it is a dilute solution, but it will slow down the process since it protects the bleach atoms from air and sun exposure.

4) Allow the pumpkin to air dry.  Sanitation is not immediate (keep that in mind for sanitizing surfaces in the home, as well) and wiping can cause cross contamination

If I can do this with a pumpkin, should I be doing this with my other produce?

The short answer is NO.  It is not recommended that home grown or purchased produce be washed with any sort of detergent or chemical in the water.  Fresh cold water and friction should be sufficient for removing soil and pathogens on the surface.  Proper protocols, equipment, and training are needed to make sure sanitation is done properly. Knowing which produce items can and cannot be washed with a sanitizer is important. However, if you are harvesting produce like pumpkins or winter squash for long-term storage you may want to consider sanitation using the above methods.

I don’t want to use bleach, can I use something like vinegar?

There are many sanitizers approved for use by produce growers for sanitation, so bleach is not the only option.  For home consumers there aren’t so many options.  Vinegar is often mentioned as a wash for produce.  I found no direct mention in produce handling guides of using vinegar on pumpkin, but most produce wash solutions use vinegar at a much higher concentration because it is much less effective at sanitation.  I found rates ranging from 1/3 c vinegar to 1 c water to 100% undiluted household vinegar for use as a produce wash.

Sources:

Sanitizers Labeled for Use on Produce (Produce Safety Alliance)

Produce Wash Water Sanitizers (UMN)

Guidelines for the use of chlorine bleach as a sanitizer in food processing operations (OSU)