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Index : Soils and Fertilization
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- 17. Organic Matter Improves Garden Soils - Top
- Preparing the soil properly before planting is probably the best way to ensure success with vegetables, herbs, annual flowers and other bedding plants. This also is true for many of the perennials that we grow here in Tucson.
The clay content of our desert soils make them dense and difficult for fine-rooted herbaceous garden plants to grow in. Loosening them to improve permeability for root growth requires the addition of organic matter. Mixing in organic matter over time will significantly improve soil texture, important for garden plants. Any organic matter is good, but some are better than others.
Canadian peat moss is one of the best forms of organic matter to incorporate into the soil. It is one of the longest lasting forms, buffers the typically high pH of our desert soils with it's acidic pH of around 4 to 4.5 and is fairly easy to work with. Packaged in compressed bales, it should be moistened before working into the soil. Because of shipping and handling, this is one of the more expensive forms of organic matter.
Ordinary peat, sometimes referred to as Michigan peat is mined from old aquatic deposits of decayed vegetation. These well decomposed bogs supply a heavy, dark organic material. It is far less expensive than Canadian peat, but is fairly short-lived, and does not moderate the soil pH significantly. For best results it should be mixed with other forms of organic matter.
Compost can be one of the best soil amendments, especially when it is being produced right at the same location. Any organic matter can be composted, and there are many ways it can be done. Commercial composting provides excellent organic matter for gardening. Best of all, it's a way to recycle garden and landscape waste into a usable product to enrich the soil. Small scale composting at home provides a ready source of organic matter. Best of all, it's basically cost free.
Manure, whether commercially produced and purchased by the bag, or picked up at a local stable is also a good source of organic matter. Fresh manure should be composted a minimum of 4 months. During that time, water should be applied periodically to wash out excess salts that can burn plants. As with all organic matter, manure should be well mixed into the top foot of soil. Never use dog or cat droppings in the garden as these can contain human pathogens!
Nutrient content of manures are low. Cattle and horse manure have one-half percent of nitrogen and potash, and one-quarter percent phosphate. Sheep and Chicken manure have nearly one percent nitrogen and potash, and one-half percent potash. Swine manure falls somewhere in between. This compares to commercial garden fertilizers that are typically 15% Nitrogen and 20% phosphate. The main benefit of manures are their organic matter and ability to loosen the soil.
Never mix fresh wood chips, sawdust or any other forms of non-composted organic matter into the soil. This fresh organic matter must be broken down by soil bacteria and fungi. In this natural decomposition process, nitrogen can be robbed from the soil and surrounding plants. Fresh organic matter, with the exception of manure, can be used as a surface mulch. Surface mulches are a benefit to garden plants because they help conserve moisture, moderate soil temperatures, and control weeds. As they decompose, organic mulches also add a basic form of organic matter to the soil called humus.
The more organic matter that can be incorporated into the soil the better your garden will grow. Given that fact, the best organic matter to use is often the type that's most available and least expensive. Try making your own organic compost. Purchased in bulk, manures and compost are relatively inexpensive. If you prefer bagged products, keep an eye out for sales at local nurseries and garden supply stores and stock up.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona 626-5161.
Material originally appeared in Arizona Daily Star gardening column, on March 14, 1999
- Updated: April 20, 2001
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