Healthy garden soil is teeming with life: there are
earthworms and micro-organisms by the millions, each with a
particular function in making soil fertile. Like any living
thing, the soil must have food. Without food, the life in
soil either leaves or dies.

Soil life eats organic matter, decomposing it and creating
a crucial soil element called humus. Humus is decayed
organic material. The process of decomposition releases
nutrients in forms that plants can absorb. In other words,
decomposition of organic material has a fertilizing effect.

But fertility is only part of the value of regularly
feeding the soil with organic material. Humus also
contributes to the  sponge-like soil texture that allows
air circulation and moisture retention. Loam -- the ideal
soil for growing plants - is a balanced mixture of sand,
clay, silt, and organic matter. Humus will bind sandy soil
or loosen hard-packed clay.

For these beneficial results (for fertility and texture),
the life in soil needs fresh food. Regular doses of organic
material will ensure that garden dirt is enhanced rather
than depleted over the lifetime of the garden. Every year,
a 30 by 40 foot garden needs around 400 pounds (equivalent
to 10 bales of hay) of organic material, but it doesn't
need to be added all at once.

Additions of organic material take a variety of forms. For
starters, chop garden residues into the soil: weeds, mulch,
and plants left after harvest. Hauling in compost by the
yard from nurseries or hauling animal manures from nearby
farms is also an option. But the easiest and most cost
effective method of continuous additions of organic
material is to grow cover crops, also known as green manures.

Cover crops are grown and tilled into the soil,
replenishing rather than removing nutrients. Even in a
small garden, this is an effective method when a harvest
crop and a green manure are grown in rotation. For
instance, plant a late summer green manure after an early
crop such as peas or broccoli.

Some suggestions for cover crops include legumes,
buckwheat, and ryegrass.

Legumes such as peas and soybeans fix atmospheric nitrogen
into the soil when inoculated seeds that attract certain
micro-organisms are used. In addition, these legumes are
vegetables, making a single planting both a harvest crop
and a green manure.

For bulk and quick growth, ryegrass or other annual grains
are good choices. In colder climates these are especially
good cover crops for the end of summer because they die
over the winter and are easy to till in the spring. For the
poorest soils, buckwheat is most useful.

Green manures can work with or without using powered
equipment, but in larger gardens a roto-tiller certainly
makes the process easier. In smaller gardens, the question
of whether it makes financial sense to invest in renting or
buying a roto-tiller has to be weighed against the cost of
hauling in compost and animal manures.

Either way - hauling or tilling - some form of additional
organic material beyond chopping in garden residues must
happen in order for the soil to function and for the plants
it supports to thrive.  

About the Author:
Life-time gardener Judith Schwader specializes in organic
gardening methods. She shares expertise, humor, and advice
for your gardening success at A to Z Gardening.
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