One of the newer “miracle products” targeted to gardeners is
rock dust. Rock dust (also called rock flour or rock mineral powder) is exactly what it sounds like. It is a
byproduct of quarry work and is generally a finely pulverized material that resembles
silt. It’s heavily promoted as a way to provide macro- and micronutrients to
your soils and plants. Is it worth adding to your gardens?
Rock crushing at a quarry
First, it’s worth acknowledging that repurposing an industry
byproduct is always preferable to throwing it away. Fortunately, the last few
years have yielded some peer-reviewed research that we can use to make informed
recommendations.
What’s in rock dust?
Obviously, the mineral content of rock dust is dependent on
the rocks used to make it. This means the mineral content varies considerably,
but in general rock dusts contain:
Large amounts of silicon, aluminum, and sometimes
iron
Lesser amounts of calcium, copper, magnesium,
manganese, potassium, sulfur, and zinc.
Potentially toxic levels of aluminum, arsenic, cadmium,
chromium, copper, lead, nickel, and sodium.
I’ve added some tables from a few research articles that analyzed their rock dust mineral content below. Note the high silcon, aluminum, and iron content. (LOI = loss on ignition, meaning some materials were burned off during analysis.)
How is rock dust used as a mineral source?
Rock dusts must be solubilized to release minerals. There
are some criteria that can speed mineral release:
Decreasing the particle size of rock dust.
Blending the rock dust with nutrient-rich organic
matter like manure. This provides an acidified environment for mineral solubilization.
When is it beneficial to use rock dust?
There are documented benefits to using rock dusts – but only
in agricultural production systems:
Rock dusts can contribute minerals to nutrient
depleted soils, such as agricultural soils that have been overworked for
decades.
Organic farmers can use specific rock dusts to
supply micronutrients, rather than commercial fertilizers which are not
certified for organic crop production.
Cereal crops – members of the grass family – require
silica as a micronutrient (though silica is rarely if ever deficient in field conditions).
Azomite is a heavily marketed garden product. New to me is that plants require 67 essential nutrients. Sounds like we need to update our plant nutrition textbooks.
What’s the bottom line for gardeners?
As one article states, “…there is a potential for using [rock
flour]…where there is a lack of these nutrients and where conventional chemical
fertilizers are either not available or not desired.”
And how do you know if you have a lack of a certain
nutrient? Why, by having your soil tested, of course! There is no point in
adding anything to your soil unless something is missing. It is MUCH harder to treat
a nutrient toxicity than to add a deficient nutrient. Iif a soil test reveals a lack of a particular
nutrient, a carefully chosen product
could supply this mineral. But you would have to know what else was being
supplied and possibly creating a mineral toxicity.
At this point, there is no evidence to suggest that rock
dusts are of any value to a home garden or landscape. And adding these products can easily
contribute to aluminum and heavy metal toxicities. I would never add it to this
soil, for instance, as it already has excessively high aluminum levels.
Aluminum is already at potentially toxic levels in this soil. No need to add more.
This blog is full of great ideas on how to manage your soil
naturally, sustainably, and safely. Rock dusts are just the latest garden
product with lots of marketing but little benefit.
It is no secret that houseplants are hot right now. Interest was growing before the pandemic, especially with millennials and younger folks. Then the pandemic hit. Houseplant interest skyrocketed since people were stuck at home and wanted to bring a little bit of nature indoors to make their spaces a little more cozy for 24/7 habitation.
This has caused the demand, and price, of many houseplants to increase, especially if they are on the rarer side. One thing that increases the price of many plants is when a variegated version of a standard plant has been developed.
My reading nook/houseplant oasis
Just as an example, after posting a photo of my “reading nook/houseplant oasis” in my home office I was informed that variegated form of a Monstera deliciosa vine that I had was the highly sought M. deliciosa “Albo-Variegata” cultivar, usually referred to as a Monstera albo, or just Albo. Folks were reaching out to buy cuttings right and left. I ended up selling 5 single leaf/node cuttings over one weekend and made $675 in the process. That’s right, $675! The most variegated of the leaves sold for $200, and that was actually a bargain price. The garden writer for the local paper, the Omaha World Herald, even picked up the story and shared it as a focus on the four new houseplant shops that have popped up in the city over the last few months.
Had my plant not had the variegation that made it an albo,
each of those cutting would have been worth a few dollars apiece. So what makes some plants variegated and
others not? Sometimes the variegation is
the standard form found “in nature” and sometimes it is a cultivar or variety
that has been bred or discovered by chance.
Let’s take a look at all the ways that a plant can get that variegation,
whether it is standard or rare.
Chimeric variegation
My Monstera albo that caused the hubub
This is a common form of variegation and the one responsible for the variegation of my Monstera. In this form, a genetic mutation in some cells changes that cell’s ability to produce chlorophyll. It may reduce chlorophyll production, resulting in yellowish or silver coloration, or eliminate chlorophyll altogether, resulting in white coloration.
The name chimeric or chimeral is based on the fact that the plant displays two (or more) chromosomal patterns on one plant. In Greek mythology, a Chimera is a frightening fire-breathing female monster with the head of a lion, body of a goat, and the tail of a serpent.
An ancient chimera statue
This variegation can be stable, where the pattern persists throughout the plant. Or it may be unstable, where it is random on certain leaves and parts of the plant can revert back to the standard green form. These plants can also produce leaves that are almost totally white, which usually results in a leaf that will die since it can’t photosynthesize.
This type of variegation also means that cutting or propagations may or may not be “true” to the pattern. It can be random. For my Monstera, the presence of white striping in or around the node that will become the new plant is the important marker for whether the new plant will be variegated or not.
One common chimeric houseplant is the plant formerly known as Sanseveria, now a Dracena (Snake plant or mother-in-law’s tongue). Many of the different color patterns on some of the cultivars are due to cuttings taken from different parts of the “original” natural type that display different colors on them.
Viral Variegation
Viral variegation that was all the rage in Tulip Mania
While beautiful, this variegation will often reduce the productivity of plants if not kill them outright. There aren’t a lot of houseplants that have this variegation, but some Hosta cultivars do. Probably the most famous case of viral variegation is the Tulip Mania during the Dutch Golden Age (in the 1600s). Prices of tulips skyrocketed and people were buying them as investments (maybe like the current houseplant craze, or GameStop stocks, or bitcoins). Unfortunately, as the virus reproduced plants kept getting weaker and weaker. Eventually the tulip market collapsed and lots of people went broke. Let’s hope that doesn’t happen with the houseplant market….at least with my fancy Monstera.
Natural Variegation
Natural variegation on Tradescantia
This type of variation occurs when the patterns or colors of the variegation are written into the DNA of the whole plant. It will occur regularly throughout the entire plant, not randomly on some parts as in chimeric or viral variegation. This variegation is passed through cuttings and usually through sexual reproduction from seeds as well, though different variations may pop up that cause a more desirable or rare cultivar.
Common houseplants such as Tradescantia, Maranta (prayer plant), and many more common plants have this type of variegation.
Blister, bubble, or Reflective Variegation
Reflective variegation on Phildodendron ‘Birkin’ following veins in the leaf
This type of variegation occurs when there is an air pocket or bubble between the lower layer of tissue and epidermis, or skin, of the leaf. The lower level typically has green pigmentation from chlorophyll and the epidermis does not, resulting in a pattern that is usually white, silver, or yellowish though other colors could appear. This pattern can be blotchy or splotchy like in some types of Pothos and Pepperomia. It can also occur along the veins of some plants, resulting in white or silver veins on green leaves, as in some Alocacia, Anthurium, and Philodendron varieties.
In conclusion…..
Even if you don’t have an expensive plant hiding in the corner, houseplants can add lots of fun and color to your living spaces. And sometimes, your houseplant obsession can even pay for itself. Online swap and sale groups have houseplant afficionados swapping and selling cuttings and plants all over the place. So enjoy your plants….and maybe you’ll find a cash cow hiding in the corner. Don’t mind me….I’m just over here propagating more Albos to fill up my “mad money” jar.
One of the most misunderstood gardening practices is mulching. There is much mulch misinformation in horticulture books, web pages and even extension leaflets. First,what is Mulch? Mulch is any substance the covers the soil surface. Mulch can be inorganic (rock), hydrocarbon (plastic) or carbon based (chips, bark etc.) While any material applied to the soil surface could be considered mulch, the benefits of mulching especially to woody plants are greatest from fresh woody chippings of tree trimmings–so called “arborist chips” applied fresh—not composted. Annual plants such as vegetable plants are often mulched as well but usually with materials that rapidly break down such as straw or some mixtures of shavings and manures. These materials are easily incorporated later when the next crop is planted. For woody plants such as trees and shrubs, mulches that persist for a longer time are desirable. Plastic mulches used in agriculture are not suited to shade trees or other landscape uses nor are landscape fabrics. Each of these deteriorate into landscape trash rapidly and do not benefit soils under the mulch layer. Stone mulches while used extensively in the South west US are not as beneficial to soils as arborist chips.
Why use mulches anyway? Mulches support healthy tree and woody plant growth in landscapes around the world. They increase soil organic matter, the diversity and functionality of the soil food web (particularly saprophytic fungi), support mycorrhizal partners of woody plants, supply nutrients and suppress weeds. Thick mulch layers increase root development, and help to suppress soil borne plant pathogens. The breakdown of woody mulches on the soil surface encourages development of soil structure, increased water infiltration, water holding capacity, and nutrient holding capacity of underlying soil layers. Well mulched trees and shrubs grow healthfully without fertilization.
So why not mulch with compost? Compost is not suited for use as a mulch around trees and shrubs. Compost is often screened and is of fine texture. Fine texture presents a few problems. Fine compost will make hydraulic conductivity with soil and allow for water to evaporate through the compost/soil interface. Thus the moisture savings we see under arborist chips will not be the same under compost. Compost is also able to allow weeds to germinate in it so the weed suppression effects of a mulch will also be lost. Composts applied as mulch can make an interface between the soil surface and the mulch layer which should always be avoided as it will impede water movement through the interface.
Another important reason for not mulching with compost is that compost is poor nutritionally for soil microbes. Composts have most of their active or labile carbon burned away during the composting process by the rapid respiration of microbes. The compost is turned aerated and kept moist until the process stops at this point it has some level of maturity. It won’t reheat when turned. The microbes have consumed most of the available carbon for their own growth and respiration in the compost pile, none of this remains for microbes in the landscape. Fresh arborists chips are full of labile carbon. When laid over the soil surface spores of fungi invade and they begin to uses this carbon for their own growth as an energy sources. Placing fresh wood chips on the soil surface is feeding the soil microbiology at the soil-mulch interface. In time (a few years) these processes go deeper in the soil and begin to feed the soil food web beneath the mulch layer. The diversity of fungi increases, mycorrhizae begin to transfer mulch nutrients to their woody hosts and pathogens are destroyed by enzymes that leach from the fungi infested wood chips. While composts supply minerals (all that is left of the feedstock after composting) they can’t supply the labile carbon as a source for microbes. Fresh arborists chips do all this and are thus the best mulch for woody plants.
Fungi eventually invade fresh mulches releasing nutrients and enzymes to underlying soils
There has been some concern lately for using mulches that are recycled as yardwastes. This concerns me as well because gardeners may be disposing of dead plants in their greenwaste cans. In theory, pathogens could be coming through the greenwaste stream to gardeners. Getting tree chips is best because there is little likelihood for soil borne pathogens since the materials are chipped branches. There is some possibility of wilt diseases (Verticillium spp.) surviving in arborists chips but little research has established that the pathogen can infect especially if the chips are stockpiled for a short time. In my own research we showed that pathogens, weeds an insects had very short survival times in stockpiled (not turned) piles of greenwaste. There is very little chance of pathogens coming to your garden from arborist chips and the benefits to your soil and perennial plants are worth the effort to get a “chip drop” from your local tree care company.
Pathogens buried in fresh yardwaste do not survive for very long
Literature
Chalker-Scott, L. 2007. Impact of Mulches on Landscape Plants and the Environment — A review. J. Environ. Hort. 25(4) 239-249.
Chalker-Scott, L., and A. J. Downer 2020. Soil Myth Busting for Extension Educators: Reviewing the Literature on Soil Nutrition. J. of the NACAA 13(2): https://www.nacaa.com/journal/index.php?jid=1134&fbclid=IwAR0cPfBl3V-3car-RPeEmlqzwW8bPEOPgND07xMTNgCOa5GkuSWtdD5WzF8
Downer, A.J., and B.A. Faber. 2019. Mulches for Landscapes UCANR publication #8672
Downer, A.J., D. Crohn, B. Faber, O. Daugovish, J.O. Becker, J.A. Menge, and M. J. Mochizuki. 2008. Survival of plant pathogens in static piles of ground green waste. Phytopathology 98: 574-554.
Downer, A.J., J.A. Menge, and E Pond. 2001. Association of cellulytic enzyme activities in eucalyptus mulches with biological control of Phytophthora cinnamomi Rands. Phytopathology: 91 847-855
Downer, J. and D. Hodel. 2001. The effect of mulching and turfgrass on growth and establishment of Syagrus romanzoffiana (Cham.) Becc., Washingtonia robusta H.Wendl. and Archontophoenix cunninhamiana (H.Wendl.)H. Wendl. & Drude in the landscape. Scientia Horticulturae: 87:85-92
Greetings from Athens, GA! I am happy to join the group of contributors to the Garden Professors blog. My name is Pam Knox, and I am an agricultural climatologist in Extension at the University of Georgia as well as the Director of the UGA Weather Network and a former State Climatologist from Wisconsin. While I don’t claim to be an expert in gardening, I do know a thing or two about how weather and climate affect plants and hope to share some of that expertise with you over time. You can learn a little more about me from my bio on the blog page.
Source: Merritt Melancon, University of Georgia College of Agricultural and Environmental Sciences
If you really like learning more about weather, climate, and agriculture, you are welcome to visit my own blog page, “On the CASE—Climate and Agriculture in the SouthEast” at https://site.extension.uga.edu/climate/, where I post almost daily about stories that have caught my eye as well as climate summaries and outlooks for the southeastern US. I plan to post on the Garden Professors blog here about once a month and am happy to answer questions at any time at pknox@uga.edu.
A simple way to compare temperatures around your yard
For my first post, I thought I would talk a little bit more about the weather in your yard and how you can learn more about it. As gardeners, you probably spend more time in your yards than I usually do, and so you have noticed that the climate of your yard or field can vary quite a bit from one spot to another. We call that “microclimate” and if you search this blog for that term, you will find several articles about microclimates in previous years, so I won’t spend a lot of time on that here.
Source: toby everard / Blaen y Cwm in a frost pocket / CC BY-SA 2.0
One easy and inexpensive way to measure how temperature varies across your domain is to use an infrared thermometer to spot-check the temperature at a variety of locations. These thermometers are used a lot now to check forehead temperatures in the age of COVID, but they are also used by HVAC technicians to check heating and air conditioning, for example. You can find inexpensive ones selling for less than $20 online, and many hardware stores have them, too. You will be amazed how much difference there is in temperature between sunny and shady locations! Don’t forget to try it at night too to see how much tree canopy can affect night-time temperatures. Of course, if you want a more systematic and scientific approach, you can follow Linda Chalker-Scott’s experience using multiple min-max thermometers as described in http://gardenprofessors.com/microclimate-follow-up/.
CoCoRaHS: Precipitation measurements by citizen scientists
One of the many things I do is to serve as a regional coordinator for CoCoRaHS, short for Community Collaborative Rain, Hail, and Snow network. This is a group of dedicated citizen scientists who take daily rainfall measurements and report them online via computer or smartphone as part of a nationwide (and now international) network of precipitation observers. Theses observations are used by the National Weather Service, drought monitors, water supply managers, and others to document local variations in rainfall at a much denser scale than other available observing networks. I am sure that some of the readers of this blog are already contributing! You can learn more about the network and how to sign up at https://www.cocorahs.org/. Please keep in mind that they do require the use of a particular scientific rain gauge, so a hardware store gauge is not likely to have the degree of accuracy that is needed to participate. A list of inexpensive vendors (costs start around $40 plus shipping) can be found on their site in the right column. By measuring precipitation at your house, you are not only monitoring your own conditions but contributing to our knowledge of water availability around the US and beyond.
I am looking forward to interacting with you all in the months ahead, and please feel free to contact me if you have specific weather or climate questions.
(A friendly caveat – this post does not lend itself well to images. So the pictures here are simply eye candy from my 2019 trip to London to reward you for considering this visually drab but important topic.)
The actual “whomping willow” in Kew Gardens
I’ve been involved in Extension education for 17 years and
one of the most important things I’ve learned is that Extension audiences want
information that’s easily understood and has obvious practical use. Most
peer-reviewed research articles are written for academic audiences, so only the
most persistent nonscientists will slog their way through pages of dense, technical
writing. It’s up to Extension educators
to accurately translate and summarize technical scientific information for use
by the public.
Epiphyte “tree” in Kew Gardens glasshouse
Extension is part of the American land-grant university system
and extends traditional academic teaching to citizens statewide (hence the term
“extension”). In addition to providing seminars and workshops to interest
groups, Extension publishes educational materials in-house and provides them at
low or no cost to their clientele.
The Bonsai Walk at RHS Wisley Gardens
But here’s the problem: the standards for Extension publications are set by each university. Unlike the peer-review system adopted by reputable journal publishers, Extension publications can vary widely in quality. Some universities have adopted a system that parallels that of scientific journals in that they require double-blind peer review. But many universities have not – and this means that looking for Extension publications on a particular topic results in a collection of materials with contradictory messages. This is incredibly frustrating to confused nonscientists and to Extension faculty who have to sift through the mess to find publications that are relevant and science-based. As a result, Extension publications are often regarded with suspicion by both nonscientists and academic faculty (who often do not have the disciplinary expertise to sort through the mess). Since I was a traditional academic before entering Extension, I have a foot in both camps.
Sunken gardens at Kensington
Nonscientists are probably not going to have the disciplinary
expertise to tease out the good stuff from the dreck. But they can look for some
indicators that will help them identify the most reliable publications. Here’s
a checklist to start the process: the more “yes” answers you have, the better
the chances are that the information is reliable.
Is the author identified? Anonymous publications
are not reliable.
Is the author an expert? Expertise is determined
by advanced degrees (at least a Master’s degree) in the subject matter.
Is the publication peer reviewed? There should
be a logo or a statement on the publication that says so.
Is the publication relevant? High-quality Extension
publications targeted towards commercial agricultural production are usually inappropriate
for use in home gardens and landscapes.
Is the publication current? Information relative
to urban horticulture and arboriculture is rapidly changing. Publications over
10 years old likely do not contain the newest information.
Are there scientific references included, either
as citations or as additional readings?
As necessary as this process is for identifying reliable
information, there can also be negative outcomes. Universities that do not have
a rigorous process for publishing Extension materials put their Extension faculty
into the uncomfortable position of having to defend their work when it’s questioned.
It would benefit all parties for every land-grant university to institute a rigorous,
peer-reviewed process for their Extension publications.
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.
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.
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.
Rubber mulch
Kelp meal
Older treated timbers
If you don’t know what’s in it – don’t use it.
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.
Have I mentioned how great arborist wood chips can be in gardens?
Container gardening is easy and mobile
It looks cute…but just don’t use galvanized tubs for edibles
While this may seem like a good use of space, the location next to a roadway means lead expsoure will be a chronic problem
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:
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.
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.
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.
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.
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.
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.
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.
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:
Roots, stems, leaves and fruits can all be destination points for heavy metal accumulation
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;
Stems are much less likely to accumulate heavy metals, as they are basically just a straw connecting roots to leaves and other terminal tissues;
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;
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.
