Healthy soil and sustainable growing

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http://www.bostongardens.com/bostongardens/articles/Gardening_is_Really_All_
About_Soil.htm

Gardening is Really All About Soil
By Liz Ball

To the uninitiated, gardening seems to be all about plants. Certainly each
of the seemingly infinite variety of trees, shrubs, flowers, vegetables and
grasses is fascinating. Artfully combining them to create landscapes and
gardens is challenging and rewarding. However, to the initiated, gardening
is really all about soil.

It is easy to take soil for granted. After all, soil is almost everywhere.
It literally comes with the territory when you buy a home or property. Soil
may be largely dense sticky clay, thin gritty sand, or powdery silt. (Only
the truly fortunate discover loose woodsy loam in the yard.)

Whichever type, this existing soil constitutes the planting medium for the
garden on the property. To improve its ability to support and nourish
plants gardeners strive to improve its structure and boost its fertility.
Fortunately, there is an abundant, inexpensive magic ingredient that makes
this job a lot easier – humus.

It is not a coincidence that the word "humus" is part of every gardener's
vocabulary and that compost piles, one source of humus, are part of their
gardens. Humus transmutes sterile dirt into fertile soil. Derived from
organic matter of all kinds, humus is the life support system of soil. The
presence of humus among mineral particles and air spaces enables soil to
nurture plants two ways. Humus creates a loose structure that
simultaneously holds moisture and drains well. Humus also creates an
environment that supports living organisms that convert soil nutrients into
a form plant roots can use, building soil fertility. In short, humus brings
soil to life.

In nature humus is constantly introduced into soil as plant debris, dead
animals, and other organic matter that decomposes on the ground. Through
the alchemy of bacteria, fungi, and other resident micro-life activity,
this organic material is reduced by degrees to its soft, spongy essence,
called humus. It permeates the top few inches of the soil through rains,
and the good offices of earthworms and other macro-organisms, where it
continually revitalizes the soil around plant roots.

This natural cycle is repeated over the seasons out in the wild, sustaining
the great forests and other natural areas. Where there is lots of
vegetation to decay and enrich the soil, such as in woodland areas, the
soil is rich in humus and very fertile. Where there is little or no
vegetation to provide the organic debris, such as at the seashore or in the
desert, the soil has little or no humus and is lean, infertile.

In developed areas, such as residential yards and gardens, where the
natural vegetation has been removed or disturbed, this natural decay cycle
is disrupted. Organic matter such as leaves, dried plant parts, prunings,
animal remains, manures, and other debris is routinely removed before it
can recycle into the soil. Intensive planting of crops, turf grasses, and
ornamental plants rapidly depletes soil of its existing humus content. Bare
soil in garden beds is exposed to the harsh effects of sun, wind, and hard
rains, which further reduce its humus content and destroy its structure and
fertility. To grow plants successfully gardeners must emulate nature and
constantly renew the soil by adding the depleted ingredient, humus.

There is no such thing as perfect soil. Every soil has problems in
structure, texture, and/or chemistry that compromise its ability to nurture
plants. The best way to confirm suspected soil problems is to submit a soil
sample for laboratory analysis through the local agricultural cooperative
extension office. Their computer printouts profile the soil content and
structure, pinpointing deficiencies. Fortunately, the addition of organic
matter, or humus, can mitigate many of these problems.

Here are six soil problems that can be addressed by adding humus:

Compaction: Good soil is loose and crumbly because it has lots of air
spaces. Plant roots are able to penetrate soil deeply for extended drought
resistance and stability. Air is also essential to the micro-life that
lives on its organic content and processes its nutrients to create
fertility. Typically soil in a home landscape is compacted, the air
compressed from it by the weight of foot traffic, construction, mechanical
yard care equipment, and harsh weather. To reduce compaction, regularly add
humus in the form of a topdressing to existing lawns. Spread a mulch of
some organic material on bare soil in beds and under trees and shrubs year
round. Dig in compost, peat moss or the like into garden beds when planting
to improve aeration.

Sandy soil: Sandy soil has large particles with large air spaces between
them. Therefore, it drains so quickly that it dries out quickly. Also,
water-soluble nutrients leach out rapidly before the plants can use them.
Humus incorporated into sandy soil acts like a sponge, absorbing and
holding moisture and any nutrients dissolved in it. Replenish the humus
content of sandy soil at every opportunity.

Clay soil: Clay soils are so thick because they have small particles with
correspondingly small air spaces between them. They tend to stick together
and cause water to fill up the air spaces. Since moisture does not drain
from this soil well, plant roots rot. Adding humus to clay soils
discourages the small particles from sticking so tightly. They aggregate
into larger clumps creating larger spaces that drain more easily and hold
air to improve soil texture.

Fluctuating PH levels: The acidity or alkalinity of soils, expressed as pH,
affects how accessible their nutrients are to plants. Reduced acidity (pH
higher than 8.0) inhibits the uptake of iron, boron, copper and other
elements necessary for plant health. Excessive acidity (pH lower than 6.0)
discourages plant absorption of other nutrients. Alter pH levels by adding
either sulfur to increase acidity or limestone to reduce acidity in amounts
indicated by soil test results. Because humus buffers soil against changes
in its pH, adding lots of organic matter to the soil will help maintain
desirable pH levels.

Pest insects, disease pathogens in soil: Soil rich in humus is alive. It
supports active microorganisms to process nutrients and harbors beneficial
macro-organisms such as ants and ground spiders that prey on soil-dwelling
pest larvae and eggs. Humus creates a soil environment that supports
beneficial nematodes and also bacteria such as milky spore that homeowners
introduce into lawns to combat white grubs. Many other resident microbes
attack and control disease pathogens that lurk in the soil. Topdressing and
mulching lawns and gardens with organic material such as chopped leaves,
compost or shredded bark products discourages soil pest problems.

Infertile soil: Soil becomes sterile over time as its humus content is
reduced by hot weather, removal of topsoil, or intense cultivation without
replacement of organic matter. The number and activity of micro-organisms
in the soil is depleted. In their absence the production of nutrients in
the soil is severely curtailed and it becomes sterile. While fertilizer
provides nutrients to plants, it does not solve a soil fertility problem.
Supporting resident micro-life in the soil is the long-term solution.
Topdressing lawns and perennial beds with humus and incorporating it into
cultivated soil every year provides a home for these organisms so they can
assure soil fertility.

Composting: Making Humus
Carbon material + Nitrogen material + Air + Moisture = Compost

The secret ingredient in this recipe is the micro life (bacteria, fungi,
and other tiny organisms), which live on the surfaces of organic material.
Acting as an elaborate food chain within a pile of yard and garden waste,
they decompose it as they eat and reproduce. Pile some moist carbon
material (dried, brown materials such as fallen leaves or straw) either
alone or with a much smaller proportion of nitrogen material (moist, green
stuff such as vegetable peelings, fresh weeds, or grass clippings) and let
it happen. With sufficient air the organisms thrive, generating heat within
the pile. Eventually the assembled yard waste is reduced to soft, dark,
humus.

In a hurry? Encourage even more feverish microbial activity by shredding
the material before piling it, turning or stirring the pile more often, or
adding more organisms such as red wiggler worms.

(We thank Ms. Ball and the National Garden Bureau for this most informative
article.)