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Although it may seem odd, the soil is a living
thing. The soil contains billions of organisms, which feed
on organic material and break it down into food for both plants
and other microorganisms. Soil has an incredible ecosystem
where the various components can supply food for each other.
Have you ever noticed how the soil under a tree is darker
and easier to work with compared to the thin layer of dirt
over a rock ledge of limestone? The dirt under the tree has
benefited from years of fallen leaves which have naturally
composted and provided humus to the topsoil.
We can create this same effect in our yard by
adding compost and using mulch. Compost adds the same elements
found in chemical fertilizers, such a nitrogen (increases
plant vigor and promotes green leaves) and phosphorus (aids
flowering and fruiting) but in smaller slow release amounts.
Compost also adds other nutrients and soil organisms, including
bacteria and fungi. Howard Garrett defines humus as "what
makes soil crumbly, soft and workable". During the process
of creating humus, the organisms produce ingredients that
help hold the soil particles together while creating air space
and increasing aeration of the soil. The increased aeration
allows roots and water to penetrate the soil easier. It is
humus and soil organisms that convert our rocky caliche into
life-supporting soil. Compost turned into humus can counter
the high alkalinity in our Central Texas soils as well as
improving drainage and water retention. It makes frequent
fertilizing unnecessary.
You can add compost to existing gardens by putting
1" of compost over the soil and then adding several inches
of mulch. For planting new perennial beds, spread 2"
of compost over the bed and then mix it with the first 6"
of topsoil. A tiller does an excellent job of mixing compost
with the top layer of soil when creating a new bed. However,
if you are working with an existing bed, a shovel and some
hard work can mix the soil and compost without disturbing
the existing plants. If you are planting a shrub, mix 25-30%
compost in with the soil. Native plants will require less
compost since they are adapted to our soil conditions. Vegetable
and annual garden beds can tolerate up to 40% compost mixed
in with the soil. Use compost as one third of a potting soil
mix for potted plants.
You can make your own compost but most of us
can't create enough compost to meet our needs. We have found
the composted sludge product Dillo Dirt (1), produced by the
City of Austin, to be priced reasonable and very effective.
However, there are many good organic products available that
can be mixed with soil when planting. Other things that can
help your soil include regular aeration and various organic
substances, such as compost tea, that help add microbial activity
to your soil.
In addition to compost, use mulch to protect
the soil. Mulch will prevent erosion; retain soil moisture
and moderate soil temperature during our summer heat. Mulch
will also provide benefit as it breaks down and creates new
sources of organic matter and ultimately humus for the soil.
In addition to helping your soil, mulch will inhibit weed
growth. Put a 2-5" layer of mulch around your trees,
shrubs and garden plants.
If you really want your soil to be healthy and
support plant growth, consider using organic fertilizers.
Organic fertilizers can increase organic matter and humus.
Synthetic fertilizers leave chemicals that can't be absorbed
by the plants and kill beneficial microorganisms. They interfere
with the natural balance of our ecosystems in the soil. Instead
of replacing missing elements in your soil - feed and grow
the natural elements provided by nature.
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