Mulching. Why mulch? What to Use?

CONTROLS WEEDS

suffocates weeds.
saves labour.
reduces competition for water and nutrients.
spares roots near soil surface, which are often damaged by cultivation.

MODERATES SOIL MOISTURE & TEMPERATURE FLUCTUATIONS

keeps the soil moist by reducing evaporation and transpiration from weeds.
buffers diurnal and seasonal temperature changes, soil stays warmer at night and in the fall, cooler during the day, and in the summer.
winter mulch decreases frost heave.

CAUTION: Mulching slows soil warming in the spring, so don't put on too early, especially on crops that like warmth. Lettuce, peas and potatoes do best in cool, moist soil; tomatoes, cucurbits and snap beans prefer a warm, moist soil. Corn should be mulched when a foot high.

IMPROVES SOIL FERTILITY AND STRUCTURE

adds nutrients as it decomposes although it may tie up nitrogen temporarily if high in carbon.
reduces leaching losses and top soil loss by wind action and rain running off the surface.
prevents soil compaction.
encourages earthworms, whose burrows aerate and drain soil.
organic matter improves soil structure.
encourages microbial growth; CO₂ evolved by microbes may be important in stimulating plant growth.

REDUCES PEST AND DISEASE DAMAGE

provides a permanent home for biological controls of pests (predators) parasites, pathogens) although may also encourage slugs and rodents. If the mulch is easily removed, slugs may be picked up and killed so this can be an easy way to control them, the mulch acting as a trap.
microbial toxins released during mulch decomposition probably help to control plant diseases. certain fungi that catch nematodes are encouraged by soil conditions under the mulch.

OTHER

prevents fruit from bruising or coming in contact with the soil, thus decreasing the risk of rot.
can markedly improve the flavour of crops, especially small fruits, (quickly decomposing materials are best for this).
a good way of planting into sod or a weedy field is to lay the mulch down all over the field some time before planting; this will kill the weeds and leave a soft, friable soil.

What to use?

DOMESTIC AND GARDEN WASTES

Newspapers (separated into sections, colour section taken out because of heavy metals such as lead in the ink, the paper held down with stones or boards)
Grass clippings (if free of weed seeds)
Weeds and crop residues (again if free of weed seeds, good for winter mulch, or can be placed under more attractive material)
Old carpet strips and carpet backing
Coffee and tea grounds, peanut shells, etc.

FOREST AND FARM WASTES

Leaves and pine needles (can be acidic)
Sawdust (it may be a good idea to add a nitrogen source underneath as sawdust or other high carbon materials may tie up the nitrogen in the soil as it decomposes)
Bark, wood chips and shavings
Hay and straw
Crop residues (corn stover, tobacco stems, buckwheat hulls, etc.)

COMMERCIALLY AVAILABLE MATERIALS

Generally we do not recommend commercial mulches as they are usually costly and/or non-recyclable. However, these may have to be used if appropriate materials are unavailable from other sources.
Peat moss (very good for improving soil texture, but will not add much in the way of nutrients; it is also quite expensive).
Black and clear plastic (good for warmth loving crops, sometimes can be obtained free from the warehouse if you ask for damaged rolls)
Paper (if you can find a source of cheap rolls of paper; this has been used on a large scale)

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Ecological Agriculture Projects, McGill University (Macdonald Campus)
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