Toby Hemenway's Bomb Proof Sheet Mulch

The sheet mulching 'formula' we are going to use in the space is Toby Hemenway's "Bomb Proof sheet mulch" as proposed in Gaia's Garden (p. 88, 2nd ed). Sheet mulching or composting in place is an easy way to prevent weed growth and build bountiful soil life, while never using pesticides or tilling. The latter are often seen as negative by permaculturists because they damage soil ecology. Sheet mulching usually entails stacking materials, mulch, compost, and manure on top of undisturbed existing soil. The diagram to the right shows the layers we will attempt in our process.

The first layer is a very thin band of manure. This is also where you'd put your soil amendments (i.e. rare metals etc.) if you needed them. This layer works to attract soil organisms like worms and beneficial bacteria from the existing soil into our raised material. The next and first real level is 1/2" to 1" of newspaper or corrugated cardboard. This barrier smothers existing vegetation and weeds converting their remnants into compost. Next, we'll layer in 1/2" to 1" of manure. Since we are using wood chippings as our primary source of mulch, we'll need to compensate here with extra nitrogen rich material probably pushing closer to the full inch if not more. Keep in mind we are going for the ideal Carbon/Nitrogen ratio of around 30/1. Since our wood chippings are about 500/1 and our manure will be somewhere aroung 20/1 we'll need to make considerable amendments to get a proper balance. Next we will add the bulk of our mulch, which will occur in a 8-12" layer. This layer makes sure that no weeds make it though from the original surface. It is also what will start to become light, fluffy, humus rich, finished compost. For the penultimate step, we add another 1" to 2" of finished compost or manure. Finally, we'll top that off with another 1"-2" of seedless mulch. Here it is important not to use materials like seeding clover, cover crops, or grasses because weeds will become a problem. Through the summer we will continue to add more manure, compost and mulch. This start in addition to our cover crops (N-fixers, Slashable Vegation, and Dynamic Nutrient Accumulators) will ensure that we have healthy active soil life.