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The Garden Plot for July 04, 2008
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: “Mulches Intro”
It’s time to mulch gardens and landscapes. Mulches suppress weeds, conserve water, and are an excellent source of organic matter. They help maintain the right temperatures for different crops and add nutrients to the soil, including nitrogen, phosphorus, potassium, and micronutrients. Mulches establish an excellent physical environment for soil organisms. They provide a good food source for many organisms which prey on plant insect and disease pests. For example, mulch may enhance the fungi that trap and consume harmful nematodes. Studies indicate that predator spiders are increased by mulching. In fact, spiders find gardens without mulch to be much like a desert. Mulches may further prevent disease by providing a mechanical barrier between old, infected leaves on the ground, and new, uninfected leaves above the mulch. Splashing of soil-borne pathogens onto plants is also reduced by mulching.
On the negative side, some mulches may release substances toxic to seeds and seedlings. These toxic substances, or Allelochemicals, may be present in the leaves of certain plant species at different developmental stages. To be safe, don’t mulch young seedlings with leaves. Leaf mulches can be applied after plants are well established.
Sometimes plant-based mulches (such as grass clippings) keep the soil too cool for warm-weather crops. This problem can be mitigated by using black plastic mulch in the row itself and keeping organic mulches between each row.
Low-nitrogen mulches (like sawdust) can tie up nitrogen and phosphorus, making both unavailable to our plants. Woodchips and sawdust are best utilized when partially decomposed, to avoid release of toxic substances or competition for nutrients.
The more coarse the mulch, the less it will affect soil moisture retention. Coarse mulches (like straw or corn cobs) are better on cool, wet, or heavy soils - especially if mulching crops that are sensitive to “wet feet”. Sandy, light, or well-drained soils do well with fine-textured mulches that pack down tightly. A mulch may be fine to use on one crop, but adversely affect another. For example, residues from plants in the mustard family may inhibit the growth of many annual vegetable crops, but are fine with which to mulch mature fruit trees. Sawdust may have an acidifying effect under some soil conditions (depending on its stage of decomposition), and thus may be great for blueberries, but terrible for celery. Try to match the mulch choice with your soil conditions and crop requirements. Test new mulches on a small portion of your garden first.
The key to obtaining the benefits of mulch, while avoiding the disadvantages, is to match mulch choices to your soil conditions and plants, apply and remove mulches at the proper times, and neither over or under apply mulches.
For more information on mulches, contact your local county extension agent.
Helen Atthowe's new short program of gardening tips
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