Sheet mulching, a layered mulch system, is a simple, effective technique for improving soil health, managing weeds without herbicides and increasing soil permeability.
Sheet mulching can be used either in establishing a landscape or to enrich existing plantings. In both cases, mulch is applied to bare soil or on top of cut or flattened weeds or turf. Trees, shrubs, herbaceous perennials and annuals are planted through the mulch, and small area can be left open to accommodate established plants.
Sheet mulch can:
- Suppress weed growth without chemicals
- Reduce labor and maintenance costs—weeds are composted in place
- Improve nutrient and water retention in the soil
- Encourage favorable soil microbial activity and worms
- Enhance soil structure
- Improve plant vigor and health, often leading to improved resistance to pests and diseases
Sheet Mulching in Five Steps
- Prepare the site. Knock down or mow existing vegetation so that it lies flat. Remove only woody or bulky plant material. The organic matter left will decay and add nutrients to the soil. Add fertilizers and amendments to this layer if a soil analysis indicates the need. Optional: "jump start" the decay of weeds and grass by adding compost or manure at the rate of about 50 lbs/100 square feet. Soak with water to start the natural process of decomposition. It is much easier to soak the ground now, before the remaining layers of mulch are applied.
- Plant the larger plants. Before installing the sheet mulch, plant any 5 gallon or larger plants specified in the design.
- Add a weed barrier. The next layer is an organic weed barrier that breaks down with time. It is essential that the barrier is permeable to water and air. Do not use plastic. Recycled cardboard, a thick layer of newspaper, or old carpets of natural fiber work well (find sources of recycled cardboard, recycled mulch and compost here.) Many paper companies offer recycled cardboard or paper in rolls of varying widths. Two or three layers may be required to achieve an adequate thickness. But, if the weed barrier is applied too thickly, the soil can become anaerobic. Overlap pieces 6-8 inches to completely cover the ground without any breaks, except where there are established plants you want to retain. Leave a generous opening for air circulation around the root crown. Wet down the cardboard or paper barrier to keep it in place.
- Layer compost and mulch. This layer mimics newly fallen leaves, needles and other organic matter in forests. Good materials for this layer include chipped plant debris, tree prunings, leaves and straw. They must be free of weed seeds. Well decomposed, weed-free compost is also a good material but it should be spread directly over the weed barrier and covered with bulkier materials such as chipped tree prunings, to optimize weed control. In total, the compost/mulch layer should be 2-5 inches deep. Many materials suitable for the top layer often have an attractive appearance, making sheet mulch a versatile practice.
- Plant the smaller plants. Punch a hole in the cardboard and place plants in the soil under the sheet mulch. Smaller plants can often be planted right into the mulch/compost layer. Add a small amount of compost around the root ball if compost has not been included in the top layer.
Commonsense Tips
In most cases, the benefits of sheet mulching outweigh the costs. However, take care to prevent these potential problems:
As with any mulch, to prevent disease do not pile materials up against the trunks or stems of plants.
Especially during the dry season, small seedlings will need protection from snails and slugs that will seek cover under the mulch.
Protect young trees from rodents with physical guards.
Adapted from: C.R. Elevitch and K.M. Wilkinson, Sheet Mulching: Greater Plant and Soil Health for Less Work, Permanent Agriculture Resources, and Geoff Hall, Sheet Mulch, Sentient Landscape, Inc.