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Most plant problems begin with soil health
By Lisa Brewer
Master Gardener Golden Plains Area
Colorado
Gardeners tend to focus on insects and disease as problems in the garden that affect the health of their plants. In reality, 80 percent of all plant problems begin with soil conditions that reduce plant vigor. The soil is a living ecosystem full of micro-organisms, insects, and worms that consume organic matter and make the nutrients available for plant use. The activity of soil organisms does much of the work of improving soil tilth. Tilth is defined as "the physical condition of soil as related to its ease of tillage, fitness of seedbed, and impedance to seeding emergence and root penetration". Simply stated, fertility, texture, and structure are the three inter-related physical properties that determine a soil's ability to support plant growth.
In the urban soils that most home gardeners deal with, there are several distinct characteristics that have to be considered. Compaction and surface crusting is common place due to foot traffic and construction activities; less organic matter is present; there is less microbial activity; and temperatures are usually warmer. Compaction is a major factor because plant roots will only grow where oxygen is available. If a plant is growing in tight, hard, poorly aerated soil, it will not do well even if nutrients are abundant.
To "open up" a compacted soil and provide a better environment for root growth, amendments must be incorporated into the soil. A soil amendment is any material added to the soil to improve its physical properties. An amendment has to be thoroughly mixed into the soil to do its job. It will improve water and nutrient-holding capacity and oxygen infiltration in the soil by increasing the pore space of the soil. This is not the same as mulching, although mulches can be used as soil amendments after they have decomposed to the point that they no longer serve their purpose as an evaporation shield on the soil surface.
There are two categories of soil amendments: Organic and inorganic. Organic amendments come from something that was alive and include things like wood chips, grass clippings, manure and compost. Inorganic amendments are manmade or mined, such as sand and gravel or recycled tire chunks. Organic amendments increase the organic matter content of soils. This is a real plus in the soils of Colorado which are typically low in organic matter due to low precipitation and reduced microbial activity.
Some factors to consider when choosing a soil amendment are how long the material will last in the soil, the texture of the soil, the salinity of the soil, and the salt content and pH of the amendment. All of these factors will depend upon the soil that is being improved and the final goals of the gardener. Improving soil with organic matter amendments should be done on a routine basis. Although not an overnight quick-fix of soil problems, it should be considered one of the best components of good soil management.
It may take up to 10 years to get a garden soil that is "text book" perfect: Made up of 45 percent mineral, 25 percent air, 25 percent water, and 5 percent organic matter. In the end, it is worth the time and effort to improve soil tilth because healthy soil equals healthy and vigorous plants.
Date: 6/21/05
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