A mulch is any material used to cover the surface of the garden soil to protect plant roots from heat, cold, or drought, to keep fruit clean, or to control weeds. Mulches help to make more attractive, higher yielding vegetable gardens.
A mulch in the garden changes the environment where the plants are growing, resulting in better plant growth and higher yields. If used improperly, a mulch can lower yields or result in plant death. When deciding to use a mulch, weigh the advantages against possible disadvantages, cost, and availability of a particular mulching material.
There are many types of mulch-ing materials, but they can be divided into two general categories: natural and synthetic. Natural mulches are materials such as straw, hay, compost, composted bark, or pine needles. Synthetic mulches are plastics and papers.
Natural mulches consist of organic plant and/or animal residue or by-products. They are generally spread over the ground surface around established plants or over the entire growing area in a layer 2 to 5 inches deep. Composted sawdust, bark, wood shavings, leaves, grass clippings, rice hulls, ground corncobs, and animal manures may also be used. Pine needles, hay, and straw are light and airy; therefore, a 4- to 5-inch deep layer is needed for them to be effective.
Most natural mulches have some fertilizer value and are good soil conditioners when worked into the soil. They improve both the physical and chemical properties of soil. Organic matter incorporated into the soil improves water-holding capacity, nutrient availability, and aeration of the soil.
Some mulching materials, such as pine needles, peat, and oak leaves are acid in nature and lower the soil pH. Regular soil testing indicates the amount of lime necessary to make any soil pH adjustment.
Finely ground peat moss makes a poor mulch. It is easily blown around by wind and becomes almost water repellent when dry. Peat is best used to improve soil organic matter content, moisture holding capacity, and structure by mixing it with the soil.
Organic mulches are summer mulches, since most of their advantages are realized in hot weather. A summer mulch protects soil from compacting rains, foot traffic, drying winds, and heat. It also controls weeds by excluding light from germinating seeds and seedlings. Mulches prevent weed problems, thereby reducing competition for light, water, and nutrients. The resulting fewer cultivations mean less crop-damaging root pruning.
By reducing the loss of soil moisture, mulches lessen the frequency of necessary watering, and garden vegetables suffer less in dry periods. Organic mulches also increase the water absorption rate of soils. The reduced soil temperatures under organic mulches encourage root growth in the upper soil layer where there is more oxygen and fertilizer.
A mulch reduces soil erosion and the splattering of soil on vegetable leaves and fruit during rains or sprinkling. This can reduce losses to soil-borne diseases.
Apply organic mulches to warm-season vegetables when the soil has warmed sufficiently for good plant growth and when plants are established and large enough that they won’t be covered. The soil should be weed-free, recently cultivated, and contain plenty of moisture. Mulching warm-season vegetables early in the growing season makes them susceptible to frost injury by preventing soil warming and by insulating plants from any warmth in the soil.
Organic mulches are beneficial when applied to cool-season vegetables like broccoli, cabbage, and English peas in midspring. They help to keep the soil from rapid warming and drying and can extend the growing and harvest periods.
Some organic mulches require changes in methods of garden fertilization. Sawdust, wood shavings, and ground corncobs are low in nitrogen. As they decompose, nitrogen is drawn from the soil, causing a shortage of nitrogen in the mulched vegetables. To prevent this, add one-fourth pound 34-0-0 or its equivalent to each bushel of sawdust, shavings, or corncobs before applying mulch. When it is time to side-dress, pull the mulch back from plants and apply fertilizer to the soil surface. With sawdust, compost, or bark, apply fertilizer to the mulch surface and water it in.
Always remember that dry mulch may catch fire.
Plastic mulches are springtime mulches. They help warm the soil, permitting early planting; promote rapid growth; provide for early harvest; and provide weed control.
Plastic mulches reduce loss of soil moisture and protect vegetable plant fruit and leaves from soil-borne diseases. Black plastic is the most commonly used synthetic mulch. It is widely available, relatively inexpensive, and comes in various widths and lengths. Use plastic with a thickness of 11⁄2 mils (.0015 inch).
Use clear plastic mulch only when soil has been fumigated to kill weed seeds. Clear plastic warms soil more rapidly than black plastic, but weed seeds germinate under clear plastic.
Warm-season vegetables like cucumbers, melons, squash, tomatoes, peppers, and eggplant grow better and produce more when grown on black plastic mulch than when grown on bare soil. Transplants can be set through plastic mulch by cutting holes with a sharpened bulb planter. Use the same tool to plant seeds of widely spaced vegetables like squash and melons.
While frequently used with warm-season vegetables, plastic mulch can be used with cool-season vegetables like cabbage, broccoli, and cauliflower to promote early growth. Plastic mulch is not used with vegetables that are closely spaced in the rows.
Black plastic mulch can also be used with plastic row tunnels to promote early growth and harvest.
Prepare the soil completely before applying a plastic mulch. Incorporate all fertilizer and lime, remove all weeds and debris, and break up all large clods. Rake the soil to prepare a smooth, level surface. Make sure the soil contains a good supply of moisture before being covered. Plastic that is 3 to 4 feet wide is best for covering a standard garden row. Select a time to apply plastic mulch when there is little or no wind. Bury one end of the plastic and unroll it down the row. Get the plastic as straight as possible and in contact with the soil surface. Cover all edges to prevent wind problems.
If you have a small garden, use large sheets of black plastic to cover the whole area rather than covering individual rows. However, this has the disadvantage of excluding rain and sprinkler irrigation from the entire soil surface. Also, wet plastic is slippery, and working in the garden when there is dew on the plastic can be hazardous.
Soils lose less moisture from evaporation with plastic mulches, so you won’t need to irrigate as often. In prolonged dry periods and with vegetables that are in the garden for a long time, supplemental water becomes necessary. The easiest way to irrigate with plastic mulch is to install a drip irrigation system, or lay soaker hoses on the surface of the rows before covering them with plastic.
Because a plastic mulch protects soil from leaching rain, the soil needs less fertilizer. When additional fertilizer is required, apply it through the planting holes and upside-down “T” slits cut at intervals into the plastic.
Although plastic warms the soil in spring, it can have disadvantages in summer. Excess heat can build up under the plastic, and high soil temperatures can injure plant roots and reduce yields. Rather than remove the plastic and lose the advantage of weed control, cover the plastic with pine needles, hay, or similar material to shade it where the crop foliage does not provide good cover.
You can spray black plastic mulch with a white latex paint after the mulch is installed or after an early crop to reduce the buildup of excess heat under the mulch. This will make it useful for summer and fall vegetables. The light-colored surface reflects much of the heat, and the other benefits of the mulch remain.
At the end of the season, remove the plastic because it will not decompose in the soil as organic mulches do.
Newspaper is an organic material, but as a manufactured product it may be thought of differently from other organic mulches. Newspaper makes a good mulch when you use a thickness of several sheets. Hold newspaper to the soil surface with soil, sticks, or coat hanger wires.
Some gardeners use a thin layer of pine needles to hold the newspaper down. Apply a newspaper mulch after plants are established. Like other organic mulches, newspaper decomposes rapidly and adds organic matter to the soil.
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