Many gardeners like to till their garden beds on an annual basis to “fluff” up the soil and provide a nice, open space for their plantings. While the appearance and smell may be appealing, few know that they are actually in many cases doing more harm than good. Tilling the soil has the following nu-intended consequences:
1) It breaks up soil aggregates which are a product of soil organic matter and biological activity
2) It disturbs and destroys populations of soil biology including bacteria, fungi, and earthworms.
3) It stirs up weed seeds and thus creates more work weeding the garden
4) Combined with rain events can lead to soil erosion
Sheet mulching is one strategy to remedy lifeless soil, inhibit weed growth, and mulch all at the same time. Not surprisingly, this is a commonly used technique in Permaculture  because it is easy, quick and effective. Whether you want to start a new garden, fill a raised bed with soil or expand an existing garden, sheet mulching is one of the easiest techniques. It’s the simple process of layering carbon (“browns”) and nitrogen (“greens”) on top of dirt, weeds, grass, or an existing garden much like making lasagna (sheet mulching is also known as “lasagna gardening”). This technique is best used with veggie transplants, tree systems, and perennial beds; direct seeding is not as successful.
Materials you will need:
– Weed barrier such as non-glossy cardboard, newspaper, phone books, or scrap paper (the bigger the sheets, the better)
– Compost or manure (this needs to be completely cured if you plan to plant directly into it)
– Mulch such as fallen leaves, straw, or wood chips
- Let existing vegetation grow as tall as possible, or if the soil is bare sow a cover crop and allow it to grow to 12 – 24″. Mow, scythe or cut your lawn, weeds, or other vegetation right down to the ground. Leave this material right there where you cut it (it will breakdown into new soil and feed the biology).
- Aerate your soil using a broadfork or a regular hard-tined garden fork. Stick in the ground and move back and forth around the entire site you plan to mulch.
- Plant any crops that will require a large planting hole (including woody plants, perennials in large pots, and large transplants).
- Add soil amendments if needed (as determined by your soil test).
- If you have compost materials that may contain weed seeds (like fresh manure, leaves, or hay), spread them in layers on the ground. Put a dry, carbonaceous layer of hay or shredded leaves below or above this manure layer. Avoid thick layers, and make sure to get a good carbon-to-nitrogen ratio just as if you were building a compost pile. Water this layer well if possible.
- Lay down the weed barrier. Use large sheets of cardboard from appliance stores if possible, because these last longer and are quicker to put down. You can use layers of non-glossy newspaper too. Make sure to have a 4- to 6-inch overlap where sheets meet so buried weeds can’t find a route to the surface. If you have already planted crops, or have other preexisting plants, don’t put this barrier over them. Rather, cut holes in the cardboard/paper to make some breathing space for each plant. A great tool for this is a hori-hori, or Japanese garden knife.
- Now you can add weed-free organic materials. Keep it simple and add a nice layer of compost or manure. Or you can do some sheet composting here; alternating layers of nitrogen-rich materials (e.g. fresh grass clippings, kitchen scraps) with carbonaceous materials (e.g. straw, leaves).
- Add your final top mulch layer, at least 3 inches thick. Water the whole bed thoroughly once again. Your sheet mulch bed is complete.
- You can plant right into the bed you made if you like. To plant a large transplant, just pull back the top layers until you get to the weed barrier (cardboard or newspaper). Cut an X into it, peel back the corners of the X and dig a hole. Throw a double handful of compost in the planting hole and then put in the plant. Pull the layers and top mulch back around the plant, water well, and you’re all set. Planting seeds is easy too. Just pull back the top mulch to the compost layer and plant your seeds. You may want to cut through the weed barrier below first, depending on how thick it is and weed pressure below the barrier. If you are planting seeds, be sure to water enough to keep them moist (could once a day in hot weather), as compost on top of cardboard can dry out quickly.
Sheet mulching can be done at any time of the year, but it best done 6-12 months before you want to garden in the space to give all the layers time to breakdown. Then the process can be repeated every year after your garden season is over. Over time, as material builds up and you get further from the seed layer, it may not be necessary to do the entire process.
Author: Falk, Elizabeth, Steve Gabriel Cornell Garden-Based Learning, updated 3.5.14
 Permaculture is a design technique for landscapes including gardens, farms, homesteads, and urban sites. Permaculture uses ecological principles based on patters found in nature. These ecological principles combined with a design method helps to create sustainable, healthy and abundant landscapes while also meeting basic human needs. Source: www.fingerlakespermaculture.org