Dan Hemenway
Amy Simone’s article “Sheet Mulching for Lawn-to-Garden Conversion” in the April 1–14 issue of The Bridge did an excellent job of introducing sheet mulching. This article builds on her piece.
Mulching is how nature builds soil in this part of the world. As you add mulch year after year, soil near the surface gets richer and richer. Earthworms create channels for roots to grow, and plants, which prefer to get their nutrients in the top six inches of soil, are in greenery heaven.
If you plan to start by sheet mulching, a few practices can improve results. First, if you are going straight to garden from lawn, let the grass grow as long as possible before sheet mulching. When mulch covers the grass, it will have more leaves to feed. The lack of light eliminates photosynthesis, by which plants grow their food. More leaves exhaust the plants’ reserves faster and they compost sooner — and become food for your garden sooner.
Some plants have their own pantry full of food in their large roots. Dandelions, burdock, and curly dock will push up through any mulch eventually. The best way to deal with them is to wait until they have produced a good sturdy top. Then push a garden fork into the soil beside the root. Wiggle the fork a bit and give the plant a tug and it will slide right out. Toss them on the mulch surface to bake in the sun and add to the depth of the mulch.
Deep-rooted plants are considered “dynamic fertility accumulators.” So adding them to the mulch retains the fertility they have sequestered right in the garden. If your mulch has important ornamental value to you, chop them into coarse pieces (especially the tap roots) and store them in a covered bucket of water for a month or two. When the roots have disintegrated a bit, you can use the contents as liquid fertilizer, a process called “fertigation” for obvious reasons.
Wood chips are best used for an ornamental garden. I would not use them in a vegetable garden because they decompose slowly and add fertility to the soil very slowly. Wood shavings (different from, and smaller sized than, wood chips) are best used for animal bedding — where chickens, horses, etc., are confined. Sawdust has a horrific appetite for nitrogen, the chemical that, in the right compounds, is essential to make the protein needed for plants and us to grow.
Fall leaves make good mulch, but avoid the leaves of black walnut and butternut trees, which poison the soil for some other plants. All parts of these trees, including the husks around the nuts, are best used to mulch a plant you are trying to get rid of.
Among the plants best not sheet-mulched are comfrey and Japanese knotweed. Alas, they are extraordinarily difficult to kill. I have seen Japanese knotweed pushing through a tarmac driveway. Comfrey leaves can be used to make a liquid fertilizer as described above. Stinging nettles makes an excellent fertility tea for the garden also. Both these concoctions stink, so make them in a covered container in a seldom-visited outdoor corner. Nightshade is an important nutrient and herbal plant.
Permanently mulching gardens, where you yearly add more mulch to keep its uncomposted depth four to six inches deep, is an excellent way to build fertility or just grow plants on top of severely compacted soil. Add a little compost with transplants. If gardening over impervious material, such as a level roof or concrete, careful attention to watering is required. Echo, a research and outreach organization in North Fort Meyers, Florida, has a demonstration that shows this works even in regions with very high evaporation rates. (Don’t let the Florida address put you off; the techniques will work even better in Vermont.)
If you are hoping to garden on extremely compacted or infertile soil, add a package of red wiggler earthworms from a bait store. They will help condition the soil while plants are growing mainly in compost. Severely compacted clay gradually accepts roots because of the earthworms tunneling.
Permanently mulched gardens have one drawback: they are a delight to slugs. I found that Chinese cabbage is an excellent slug trap, however. The slugs gang up on individual plants, so I would go out in the mornings and toss the most infested plants, slugs and all, into the chicken yard, so the slugs become a resource. If you don’t have ducks or chickens, put slug-infested plants into a bucket of soapy water and store with a tight lid. Once the slugs die and break down, the slug soup can fertigate your garden.
Love your garden and your garden will love you back.
Dan Hemenway has co-managed youth gardening projects and served as horticulturist for a Massachusetts prison, where he taught organic gardening, solar design, permaculture design, and more. Disclosure: Hemenway is the father of the editor of The Bridge.
Further reading: check out books by mulch pioneer Ruth Stout, and “Lazy Ass Gardening” by Robert Kourik.
