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March 2000 |
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More on Mulch |
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More on Mulch Jim Jarman
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Although the use of colored plastic mulches can improve garden produce production and quality, it can not solve existing problems or magically make a garden productive. The use of something like a red plastic mulch under tomatoes should be used to improve existing good production. Plastic mulches should not be even applied until three major things are at their optimum. First, the soil should be in good condition. It should have enough organic matter so the structure is loose and crumbly. There should not be any large clods and compaction of the soil will create big problems. Mulches can cut down on the exchange of soil gases and air. Roots use oxygen to grow in the absence of light and give off carbon dioxide (C02). The loose soil structure will allow C02 to be channeled to the mulch opening to be used over by the plant's leaves and fresh air to move into the soil. Second, the soil should have a good level of fertility. Once the soil under the plant is covered, it is hard to add fertilizer. The fertility should be well mixed into the soil down through the root growth layer. Third and lastly, the soil moisture level should be at or near field capacity when the mulch is applied. Like fertilizer, it is difficult to add moisture after the mulch is down. Too much water will tend to compact the soil, limit the amount of air exchange, and hold this excess water around the roots for a relatively long time. Waterlogged conditions in the soil will also allow nitrogen nutrients to escape from the soil as a gas. One-thing commercial growers and even some home gardeners use to avoid moisture and fertility problem under plastic mulch is a trickle irrigation system. Trickle irrigation systems meter small amounts of water under the mulch all during the growing season. Fertilizer is added to the irrigation water to supply the nutrients. Two other things trickle irrigation adds to gardening is increased expense and increased management. Now is the time to make a pitch for organic mulches. There are a wide variety of natural materials that can be used to make mulches, which can provide all the benefits of plastic mulches except for reflecting certain useful wavelengths of light. Most have the added advantage of allowing moisture to flow through to the soil. In vegetable gardens, think of a material that will breakdown to provide organic matter for the next season and is easily available and cheap. Three materials to come to mind are grass clippings, leaves, and newspapers. These are typical items we are wanting to dispose of that can be used. Grass clippings have the disadvantage of being rather wet when fresh and will compact into a tight, air excluding layer. If they are thick enough, they will not rot to compost but turn to something like stinky slimy silage. Clippings should be spread thinly to allow drying. Also, grass clipping have lots of nitrogen and will break down to compost in the soil quickly when till in. Leaves are dry and low in nitrogen. They will rob nitrogen for the garden plants as they breakdown. Some method may have to be employed to keep leaves from blowing away from mulched plants. A good combination of materials is grass clipping and leaves. Unfortunately, they do not occur at the same time. Still, the nitrogen from the grass clippings will aid the leaves to breakdown. The "book" says that both of these materials should be composted before use as mulch. Since there are no garden police except for maybe neighbors, friends, and relatives, you can try just about anything. Home gardening should be more of an art than a science. At least that is what I always used to say. The internet has words of information on the subject of mulches of all different types. The University of Missouri Extension Office has two guide sheets on the subject. They are: G 6960, " Mulches", and G 6958, "Grass Clippings, Compost and Mulch: Questions and Answers."
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