Easy Gardening...Mulching
B. Dean McCraw
Extension Horticulturist
Texas Agricultural Extension Service

Mulching your garden shows you really care about your plants. A mulch is any substance spread on the ground to protect plant roots from heat, cold or drought or to keep fruit clean.

Mulching is a long established horticultural practice. Farmers know that shallow cultivation of the soil's surface after a rain slows the rate of water loss from the soil. The shallow layer of dry surface soil acts as a mulch.

Mulches can be classified as inorganic or organic. Inorganic mulches include plastic, rocks, rock chips and other non-plant materials; whereas, organic mulches include straw, compost, sawdust and similar materials. Plastic is the only inorganic mulch used in vegetable gardens.

Value of Mulches

A thin layer of mulch on the soil surface (especially in sloping gardens) reduces the washing away of soil particles by rushing water. Also, mulches prevent raindrops from splashing on the soil surface. See figure 1.

Saving soil moisture is an important use of mulch in Texas. A mulch layer on the soil surface allows the soil to soak up more water. Mulch also reduces the rate of water loss from the soil. A 3-inch layer of mulch on the soil surface dries much faster than the soil below it. Thus it prevents water from moving into the air. See figure 2.

Mulches modify soil temperature in home gardens. Applied in late fall, winter mulch insulates plant roots, crowns and stems of winter crops from extremely low temperatures.

Proper mulching in summer months keeps the soil cooler. Soil covered by black or clear plastic or dark organic mulch in early spring warms faster than bare soil. This allows earlier planting of warm-season crops. See figure 3.

Use light-colored paper such as newspaper in summer to keep the soil cooler. Organic mulches such as compost and sawdust also keep soil below the mulch layer cooler in summer. Dark soil warms much faster than light-colored soil. See figure 4.

Organic mulches enrich the soil as they decay and provide a better environment for plant growth. Soils high in organic matter are easier to till and better suited to vegetable gardening. Adding organic material makes soils more crumbly, especially clay soils that pack and crust.

Mulches help plants by gradually increasing soil fertility. An organic mulch such as straw or newspaper can be turned under the soil at the end of the season. This helps build the soil's organic matter content. Turn the mulch under as soon as the gardening season is over so it breaks down before the garden is replanted.

Most mulches also provide excellent weed control. Mulches do not prevent weed seeds from sprouting. However, weed seedling emergence is blocked by a mulch layer thick enough to exclude light. A 3-inch layer of mulch on the soil surface keeps most annual weed seedlings from coming through. See figure 5. Weeds that bread through are removed more easily from mulched soil. Hard-to-control weeds such as nutgrass and johnsongrass may come through the mulch layer but can be pulled more easily or covered by fluffing the mulch with a fork.

A well-mulched garden can yield 50 percent more than an unmulched garden the same size. Space rows closer as there is little or no need to cultivate the soil. Plant food is more available in cooler soil, and the extra soil moisture increases plant growth and yields. You will harvest more fruit because of less fruit rot. Fruit does not touch the soil, and soil is not splashed up on the fruit. See figure 6. This is true for tomato fruits that rot easily when resting on the soil surface. Potatoes can be mulched heavily as the vines grow. This causes tubers to form in and under the mulch layer. These potatoes are less susceptible to soil rot, easier to harvest and less likely to be bruised during harvest.

Garden mulching reduces maintenance. A good mulch layer eliminates the need for weeding, and mulched vegetables are cleaner at harvest time. Fruits of tomato, melon and squash plants never touch the soil.

Mulching Materials

Many materials are available for mulching a garden. Some examples are: compost, straw, gin trash and sawdust.

• Compost is generally the best mulching material for the home garden. It is usually free of weed seeds and is inexpensive. Prepare compost from materials present in your yard. It is not necessary to purchase expensive materials for mulching.
• Straw is short lived and coarse textured. More straw is needed for the same effect as compost or lawn clippings. Generally, less of the finer-textured materials is required to provide a 3-inch layer of mulch after settling. compost, however, usually requires only about 4 inches to provide a 3-inch mulch layer.
• Gin trash is commonly available in Texas. It is risky to use, however, without knowing its source and prior treatment. Make sure that the farmer did not use arsenicals on the cotton. Arsenicals are long-lived chemicals that can be present in gin trash for several months or years. Also, gin trash may contain weed seeds and diseases. Compost gin trash before applying it to your garden to make it safer and easier to use. The heat generated by composting kills most weed seeds and most disease organisms that infect plants.
• Sawdust is commonly available especially in East Texas. If well managed, it can be a good mulch. It can result in a temporary, but sharp, decrease in soil nitrogen. Add a small amount of garden fertilizer to the soil after applying sawdust directly to a garden. Even better, add nitrogen to sawdust, then compost it before spreading it on your garden.
• Plastic is an effective mulch if used properly. Use black plastic in the spring and early summer to warm the soil. Black plastic keeps light from the soil and prevents weeds from growing. Clear plastic warms the soil, but weeds can grow beneath the plastic. A disadvantage of plastic is that it cannot be turned into the soil at the end of the season. See figure 7.

Selection of Mulching Material

When selecting materials, consider these factors:

• Cost of the material. Do not spend money on mulching material when suitable materials are available at little or no cost.
• The crop you plan to much. Never use material from the crop that is to be protected. For example, do not use potato vines from the spring crop to mulch fall potatoes for the possibility of disease is increased.
• When the mulch is to be used. Select a light-colored mulch during the summer and early fall to reflect heat. Use a dark-colored mulch in early spring to help warm the soil to permit earlier planting and hasten early growth.

Using Mulches

Spread mulches on freshly cultivated, weed-free soil before plants are large enough to interfere. Apply organic mulch thick enough to leave a 3-inch layer after settling. Four inches of fine materials like compost should be adequate. Remember that coarser materials, such as straw, settle and may require 6 inches or more initially. If you use newspaper, place three layers on each side of the row. see figure 8. Add more mulch during the season if you are working with organic materials. The mulch settles and gradually rots during the growing season where it meets the moist soil surface. Adding additional layers assures continuous weed control, a clean resting place for the fruits of your labor and creates a pleasing appearance all season long.