Problems with sheet mulch/ farm update

We have installed lots of sheet mulches on the Lakewood farm. Sheet mulching involves laying an overlapping layer of cardboard to smother weeds, and then piling on a foot or more of organic matter, ideally weed free, and with a balanced ratio of nitrogen to carbon. There are lots of benefits to this: less weeds, more organic matter, and, after the first year, less work, since the beds are never tilled again. For more information, see this post.
However, we have discovered two potential problems with sheet mulching.
First of all, sheet mulch does NOT stop bindweed. Those long twisting roots easily wend their way around the cardboard and through every crack, to emerge triumphantly at the surface. However, nothing else really kills bindweed either, and sheet mulch at least makes bindweed easy to pull. And the sheet mulch killed off the grass, thistles, dandelions, mallow, and other weeds on our site fairly well.
The second problem is more serious. When we planted the tomatoes, we just opened a hole in the mulch, stuck the tomato in, and pushed the mulch back together. Some of the beds were full of a light, fluffy mixture of grass clippings and mulched leaves. We then got a lot of rain, and occasionally people would step on the beds (our paths are not that well defined.) The mulch compacted and sank. Soon the tomato root balls were sticking out of the mulch, where the peat in the potting mix acted like a wick to dry out the roots. The fact that the grass clippings were very porous did not help matters any. We first noticed the problem when a lot of the tomatoes looked sick, with curled and yellowing leaves on a hot day.
Hopefully, we have solved the problem by laying a layer of rough compost from the pile we built last year over the beds. This will cover the root balls and hold water.
So, if you want to build a sheet mulch:
Don’t expect it to kill bindweed,
Try to mix dried grass clippings with other, more compact and water retentive material,
Lay the mulch much thicker than you think necessary, and plant deeply,
Carefully pack mulch over the root balls of transplants,
And ideally, build the beds in the fall, so they can decompose and compact over the winter.
The tomatoes in our hugelkulture/ sheet mulch hybrids are doing splendidly so far. I will continue to report on the success or failure of our systems over the next year. And now we will know how to avoid this problem for the future.
We are almost done planting. We have also got a fence built on the perimeter of the property, set up plant supports, and done a lot of weed mowing on the site over the last few meetings.

 

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Notes from the meeting of October the fifth/ bindweed

At this meeting we got another hundred and fifty feet of sheet mulching done, and repaired a mistake we made in our hugelkulture last time. We had built a mound of sticks, only to realize that many of them were from a willow tree; and willow branches sprout if stuck in the ground. So we would have had a thicket instead of a raised bed. We removed the willow branches and built a new pile of Siberian Elm and Green Ash. At the next meeting we will add some more wood and cover the pile.  (Willow can be used in Hugelkulture; it just has to be thoroughly dead first.)

Our neighbor to the east cut down a line of Siberian elm along the fence, giving us even more branches to clean up, and a lot more light in the morning. He will be planting evergreens there, but they will take a while to grow.

We took soil samples to do some basic testing on, and some lead testing, since parts of our site were filled in the past. If lead is found in certain areas, we will take steps to tie it up, and only grow fruiting plants there. (Fruit, unlike leaves or roots, does not accumulate lead.)

We found that bindweed had infiltrated our pile of manure from the ground underneath and all the little snippets of root we had accidentally moved to the sheet mulch with the manure were sprouting ABOVE the cardboard. Fortunately they are not well rooted yet, so we are carefully pulling them out now. But I decided to do some more research on it, since some will almost certainly make it through our sheet mulch.

Bindweed is literally a superplant. Its seeds last for fifty years in the soil. A plant can grow twenty-five feet in a single season. Drought, compacted soil, and heat make no difference to it whatsoever. Some say that a root system can be two miles long! While this might be exaggerated a bit, it definitely possesses enough root resources to outlast almost any gardener’s pulling efforts.  It can outcompete many garden plants, tangling them up till weeding is impossible. A tiny piece of root or stem will grow a new plant.

The roots are brittle, making removal difficult. They are herbicide resistant, hard to smother, and can’t be solarized in this climate.

There is dispute about their medical value. Some say they are poisonous, others say they are a useful anti-cancer medicine and tonic. And there is no doubt that they help heal damaged soil, and that cows love them.

But, we don’t have cows, and I think we can improve our soil just fine without this plant. So, what to do?

There are a number of ways to weaken bindweed.

  • A deep mulch, especially when backed with cardboard, will kill some plants and weaken any which make it through. It will then be vulnerable to persistent pulling action when small, as the roots will come easily out of a loose mulch. This will starve the plant.
  • A rye cover crop secretes substances which temporarily suppresses bindweed. A traditional sequence of cover crops is rye and vetch overwinter, then buckwheat, then rye and vetch again for another winter, and then vegetables the next spring.Loosening the soil with a digging fork disadvantages bindweed, whereas tilling just encourages it;  disturbed soil increases its growth, and the tiller spreads root pieces to fresh ground.
  • Since bindweed is a pioneer plant, it thrives in a poor soil. If the soil is improved bindweed becomes weaker.Geese, chickens, and pigs eat bindweed. A ‘chicken tractor” moved across land may destroy the plants.
  • Plants can be coiled up and placed beneath a rock, or in a bag. This cuts off sun from the leaves, but is more effective then pulling. Breaking the plant releases a hormone which increases its growth.They can be liquified or fermented and used as fertilizer.
  • Some Sunflowers, squash, legumes, Mexican marigold, and alfalfa are allopathic to bindweed, though they will not wipe it out. So are a few weeds; dandelions, and Lambs-quarter. We don’t want any more dandelions, but some lambs-quarter might be good, since it is edible. (Dandelion is too, but we have enough of it around.)
  • A deep cedar mulch kills bindweed.
  • They need an alkaline soil; if the soil is acidified, they weaken and disappear.
  • Horticultural vinegar can kill the leaves.
  • Some bugs can be released which EAT bindweed. However, these don’t do as well on irrigated sites

We will probably employ a number of these strategies. We are already laying down a heavy mulch; in the spring, we will plant allopathic plants anywhere the bindweed comes back, do a lot of hand pulling, and maybe get some hungry chickens.