Tuesday, October 7, 2008

Sheet Mulching Technique

Greater Plant and Soil Health for Less Work

Once you get the hang of it, sheet mulching can be used anywhere plants are grown in the ground. Sheet mulching may be used either in establishing a new garden or tree planting, or to enrich existing plantings. In both cases, mulch is applied to bare soil or on top of weeds. New plantings are planted through the mulch, and a small area is left open to accommodate established plants and trees.

The benefits of mulching justify putting the energy into doing the job right, using ample materials. Collect all of the materials, and complete the mulching process in a day. A reduction in maintenance and increase in plant vigor will reward the initial effort.

Sheet mulch is put down in layers to mimic natural forest mulch: well decayed compost, weed barrier, partly decayed compost and raw organic matter.

Step 1: The Concentrated Compost Layer
To prepare the site, knock down tall weeds and woody plants with a brush cutter, scythe, or simply by trampling the area. Then proceed to lay down the sheet mulch.

Whether you are mulching bare soil or weeds, the first step is to "jump start" microbial activity by adding enriched compost, poultry or stock manure, worm castings or the like at the rate of about 50 lbs/100 square feet. This high nitrogen matter stimulates soil life and gets things going. If the soil is acid, which it likely is if the area has been disturbed recently and treated with conventional fertilizers, add a layer of lime or crushed coral. A soil analysis will indicate the need for adjustment of pH or mineral amendments. This is the appropriate time to add the recommended doses of amendments such as rock phosphate and K mag.

Soak the area well with water when the amendments are dispersed.

Step 2: The Weed Barrier
Most cultivated areas today harbor untold numbers of weed seeds. There are also weed seeds carried around by wind, animals and people. Soil borne seeds are lying dormant and waiting for the right conditions to sprout. Simply pulling or killing growing weeds will not erase the weed problem: more seeds will sprout almost as soon as the soil is exposed to moisture and light. Therefore the next step in mulching is to put down an organic weed barrier. This barrier prevents the germination and eventual emergence of weeds through your mulch.

Underneath this weed barrier grasses and weeds die and quickly become food for earthworms. From now on, the worms turn and aerate the soil, as they do naturally when in the right environment.

Of the four sheet mulch layers, the weed barrier has no natural counterpart on the forest floor. In the forest, weeds do not sprout because there is "no room for them," which simply means a lack of space above and below the ground, and a lack of light. By planting an area properly, there will eventually be no room for weeds. The weed barrier is needed only for establishment of the mulch, and disappears with time. If your area is planted appropriately, weeds will not emerge after the decomposition of the weed barrier.

Materials for the weed barrier that work well are: 4-6 sheets of newspaper, cardboard, burlap bags, old rugs of natural fiber, worn-out jeans, gypsum board, or whatever you can find around. Banana, ape and ti leaves also work if laid down in several layers. Overlap the pieces of the material so as to completely cover the ground without any breaks, except where there are plants you want to save. Around these leave a generous opening for air circulation around the root crown. Care in laying down the weed barrier will save you the headache of emerging weeds later on.

Step 3: The Compost Layer
This layer is on top of the weed barrier - it must be weed seed free. Well conditioned compost, grass clippings, seaweed and leaves are ideal materials to spread over the weed barrier. Any weed-free material mixture at the right moisture level for a good compost will do. This should form a fairly dense layer about 3 inches thick.

Step 4: The Top Layer
The top dressing mimics the newly fallen organic matter of the forest. It also must be weed-free. Good materials for this include leaves, twigs and small branches, fern or palm fronds, straw, coffee chaff, macadamia nut shells, wood chips, sawdust, bark, etc.. The top layer will slowly decompose into lower layers, and therefore must be replaced periodically; it represents reserves of compost. This layer should be about 3-5 inches deep. Many materials suitable for the top layer often have a pleasant cosmetic appearance. What luck! For this reason, there should be no hesitation in using sheet mulch in all cultivation from landscaping to gardening to permanent orchard crops. In fact, as you use mulch, bare soil will begin to seem ugly and undesirable.

When the soil is amended and sheet mulch applied properly, there will never be a need to turn the soil. Earthworms do the tilling. The only task left will be to keep the soil covered by replenishing the mulch.

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