Sheet-mulching: composting in place

Cardboard, an excellent source of carbon, placed around our winter squash mounds.

We all know the wonders of good compost in the garden, but turning piles can be laborious. And spreading it wheelbarrow after wheelbarrow to the beds is lot of work.  Well worth the effort, don’t get me wrong.  We have an extensive operation here on LSSI, but we also use another method to build soil. It’s called sheet-mulching, a.k.a. composting-in-place or lasagna-gardening.
If you have a manure source or a load of coffee grinds and leaves, you’re in good shape.  We need nitrogen (think: manure, coffee grinds, vegetable scraps) and carbon (leaves, paper, cardboard). Whatever sources of wastes you have you just layer them right on top of the ground you intend to grow in and let it break down in place.  A great time to do this is in the fall, so it can degrade over the winter. Come spring, you’ve got soil ready for your seeds and transplants.
Here’s the method:
  1. Soak the planting area. Water heavily. Let sit overnight.
  2. Slash vegetation, weeds, veg. residue, roots and all, and leave as “green manure.” Do remove stumps or woody vegetation, however.
  3. Amend your soil with lime, sulfur, gypsum, any raw mineral, etc. as needed.
  4. Take a spade fork or pitch fork and crack the earth open a little. Don’t turn the earth, “just poke some holes to create better moisture retention, root penetration, and soil-critter movement” as Permaculturist Toby Hemenway says.
  5. Put down a thin layer of nitrogen material: manure, cottonseed meal, fresh grass clippings, or other lush greens or veggie scraps.
  6. Spread cardboard or newspaper to smother weeds.  Cardboard is a better suppressant because it’s thicker and takes longer to break down. (Be sure to remove tape, etc. and DON’T use the produce boxes covered in wax or lots of colorful dye.) Overlap sheets and SOAK them.
  7. Add another thin layer of nitrogen-rich material.
  8. Pour on the bulk-mulch: 8-12 inches of straw, hay, yard waste, leaves, seaweed, saw dust, etc.
  9. Add an inch or two of finished compost if you have it. 
  10. Then another final layer of carbon.
    A word on C(carbon):N(nitrogen): As you layer, pay attention to the C:N ratio. It will ideally be at 30:1.  Get an idea of what the content of your materials are.  For instance, if you’re working with sawdust which has a very high carbon content of  500:1, you’ll want to be sure to add a lot more nitrogen, than if you’re layering with tree leaves. 
     

    from Steve Solomon’s Gardening When It Counts
    Now, sheet-mulching is not an exact science and the method is pretty forgiving, especially if you’re giving it six months to break down.  Just sure to add both the elements as you have them and you’ll be doing wonders for your soil. 

 

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