Since our soil has high levels of lead in it, I’m concerned about growing in the soil at all until it’s been amended. My permaculture background brings me to sheet mulching as the answer to our lead problem. The problem is that I’ve don’t have much experience with it; I did an installation once but never found out the results of our efforts. So I started to research.
The recommendation is to use 4-6 layers of different types of compostable organic matter, creating a bed no larger than 200 sq. ft. that is 2-4 ft. deep. The ground should be wet before starting. Here’s a list of layers:
- 1st Layer – High Nitrogen Layer (worm compost, manure, etc.)
- 2nd Layer – Cardboard/Newspaper – dampen before moving on
- 3rd Layer – Another High Nitrogen Layer (manure, fresh grass clippings)
- 4th Layer – Bulk Mulch (8”-12” of loose straw or hay) – Should be damp but not wet
- 5th Layer – Compost (1”-2”)
- 6th Layer – Weed- and Seed-free Organic Matter (2” of straw, fine bark, or wood shavings)
All of these don’t have to be utilized, “sheet mulch can be as simple as a layer of newspapers topped by eight to twelve inches of nearly any mulch material” (Hemenway pg. 88) however this is the optimum plan.
I’m not certain how many of these layers we are going to end up installing; however we have a couple already taken care of. I fortuitously picked up some very large sheets of cardboard from a colleague last week which are going to be using for the 2nd layer, what that doesn’t cover we have newspapers. We need to get the bulk mulch and figure out something to use for the high nitrogen (N) layer. I have some worm compost which could be used for the N layer but I doubt there’s enough to cover the entire area so we might have to consider getting some fresh manure for this task. We have some connections for bulk mulch but need to confirm where we are getting it from.
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Dump truck dropping off compost |
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Compost spread out |
According to Toby Hemenway, “if you plan to plant the sheet mulch within a few weeks, a layer of compost will be necessary to act as a seedbed” (pg. 89). Luckily back in October we had a truck load of compost delivered to the site and we leveled it out to about 2’-0” deep, it’s currently 4”-6” of compost; which will be perfect for us to use for the 5th Layer.
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Compost after winter |
Finally, we need secure the weed- and seed-free organic matter. The fact that its weed- and seed-free is important otherwise the garden will be overrun with weeds, which is exactly what we are trying to avoid with this layer. When we are ready to plant in May, Toby recommends pushing “this layer aside to reach the compost/soil layer right below” (pg. 89).
Hemenway, Toby. (2009). Gaia’s Garden: A Guide to Home-Scale Permaculture (2nd Edition). White River Junction, VT: Chelsea Green Publishing Company