We’re in for another very dry year in California and much of the American West. Snowpack levels are extremely low in the Sierras. Rainfall has been a fraction of normal. A state of emergency has been declared in California and parts of Oregon and Washington. Water will be expensive, not very good and we’re almost sure to see water rationing. It’s not as bad as the photo of Death Valley above, but we’re in for a very dry summer. What can a gardener do?
Organic mulches that decompose into the soil are the best for the soil biology and the long term health of the garden. Unfortunately we need to be very cautious with the materials we buy or bring into our gardens. There is a real danger that contaminated compost, manure, straw, hay or grass clippings will destroy your garden and keep you from growing veggies for years. We know this from experience! Read on!
Sadly, some very toxic and persistent broadleaf herbicides are being used on grass family crops, golf courses, in ditches and under power lines. The first reported garden contamination occurred in England. Gardeners were using manure from herbivores pastured on land treated with these herbicides, and the compost made from the manure was killing their tomato and other vegetables. Another instance was in Seattle. The herbicide contaminated materials passed through a commercial composting operation, and ruined people’s gardens for years. These material also have contaminated straw from eastern Washington, where these herbicides are used to control Canadian thistle. These very persistent herbicides have the capacity to contaminate straw, hay, compost and grass clippings. They can pass through an animal intact and contaminate their manure. If these contaminants get into your garden they will stunt and kill your plants for years! If you are bringing in mulch materials that you don’t know the full history of, it pays to test the materials before risking your garden.
The herbicides are Picloram, Clopyralid and Aminopyralid but they are sold under the trade names of:
We use this procedure to test any imported material:
Better yet, also maintain a control.
The following alternative procedures are widely reported on the internet.
To test compost or manure…
Fill another three clean pots solely with commercial potting soil. These will be the untreated comparisons.
To test straw, hay or grass clippings…
In both tests there is a possibility that your pea or bean plants will not do well for reasons other than herbicide residue. Photos of herbicide contamination are on this Washington State University website.
In the vegetable garden we use a layer of compost or “proto-compost” (for example, garden waste or mushroom compost that hasn’t fully broken down yet – see picture at right) as a local mulch around the plants. The density of compost and proto-compost is good for holding moisture around seedlings or transplants and the part in contact with the soil gives the soil biology something to munch on.
Note: We don’t use vermicompost as a mulch — it belongs in moist soil below or near plant roots where the microbes in it can spread out and multiply.
Over this we spread a hefty layer of straw. Straw is the stem of grain plants (oats, barley, rice) after the seeds have been removed. Straw is not the same as hay. Hay is the stem and the seeds of plants and is usually grown as a feed for animals. The seeds in hay, even rotted hay, happily sprout and grow in the moist conditions under the mulch.
We also use a thin layer of broken down straw to cover the dirt over newly planted seeds (last years straw works well for this). The bits of straw keep the sun off the soil and help keep it from drying out and crusting over.
Leaves make a great mulch, as does pine “straw” (fallen pine needles).
Grass clippings are dangerous! They have enough nitrogen to heat up and literally burn your plants if fresh clippings are used. Dry your clippings before use or keep them a few inches away from the plants.
Wood chips do not work well in the vegetable garden near the plants. They are great for mulching paths, and around raised beds if you got ’em. The problem is that when they decompose, they tie up nitrogen, and nitrogen is one of the most difficult nutrients to make available in an organic garden. The same is true for sawdust.
We saw one very inspiring YouTube of a man in Washington state who mulched his entire garden with wood chips. It looked great and the plants looked great. Then he let it slip — he’d put a 6″ layer of composted chicken manure under the wood chips. Chicken manure is one of the highest nitrogen manures around. Apparently it had enough nitrogen to supply the decomposing wood chips and grow a good garden.
Ideally every part of the garden will be mulched, including the paths and surroundings. There is something to be said for the communication that happens between plants when all of the soil is covered.
Under the right conditions many plant species will form a symbiotic relationship with a type of soil fungi (arbuscular mycorrhizae or AM). The fungi penetrate the roots of the plants and grow out into the soil, bringing back minerals and water for the plants. The plants in turn feed the fungi carbon. The fungi acts like a second set of roots, providing some degree of drought tolerance.
AM tends to be comparatively sparse in soils with adequate minerals and moisture, probably because under abundant conditions the plants are not feeding them carbon to stimulate their growth. For those of us who keep our soil well mineralized and moist, AM are our insurance policy. If anything comes up short, our plants can send out the AM to get it.
Tilling (plowing, rototilling, spading, etc.) breaks up the fungal strands, but they grow back in about a month.
About 80% of plant species form an association with AM. Garden plants that do not are:
Cabbage, broccoli, cauliflower, radishes, turnips, kale, bok choi, and other plants in the brassica family.
Endomycorrihzal fungi is sold in a powdered form for inoculation of soils. We have not been able to tell one way or the other whether the inoculant works.
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