Using a mulch in the vegetable garden has become a very popular and almost necessary item. Mulches perform many duties in the garden by suppressing weeds, controlling water runoff, helping to control some garden pests, and also by creating a more attractive garden space.
Personally, I never used any type of mulch in my vegetable garden until this year, and now I swear by it. Adding mulch to my vegetable garden has decreased weeds to almost none. I may have to pull a tiny weed or two every couple weeks, compared to when I did not use mulch, I needed to pull weeds almost every day. That alone has sold me on the importance of using mulch.
Many gardeners that have never used mulch in their vegetable gardens before may wonder which type of mulch is best. It really depends on what is readily available in your area, and what you are growing in your garden.
Mulches for the Vegetable Garden
Here are the two types of mulches you can use in your garden, and examples of each type:
Organic Mulches for the Vegetable Garden
A 2-inch layer of sawdust provides good weed control. Fresh sawdust contains a great deal of carbon and very little nitrogen, and its breakdown requires that microorganisms take nitrogen from the soil. A very thin layer of sawdust, about a 1/4 inch, is useful in starting seeds because it helps keep moisture in. There is often a problem with crusting of fresh sawdust, which can make it difficult for rainfall to soak through. Sawdust is best used for vegetable garden paths and around permanent plantings. Readily available from sawmills, it tends to be inexpensive.
Hay or Straw
A 6- to 8-inch layer of hay or straw provides good annual weed control. These materials decompose quickly and must be replenished to keep down weeds. They stay in place and will improve the soil as they decay. Avoid hay that is full of weed seed and brambles. Fresh legume hay, such as alfalfa, supplies nitrogen as it quickly breaks down. Hay and straw are readily available in rural areas, but city dwellers may not be able to obtain hay easily. Straw, on the other hand, may be purchased at most garden centers, often commanding a high price. Both are recommended for vegetable and fruit plantings.
Baled pine needles are also found in garden centers for use as a mulch. Pine needles and pine bark should be watched closely in vegetable garden as they can raise the acidic levels of the soil.
A 2-inch layer of grass clippings provides good weed control. Build up the layer gradually, using dry grass. A thick layer of green grass will give off excessive heat and foul odors rather than decompose as other organic material. However, in limited quantity, clippings will decompose rapidly and provide an extra dose of nitrogen to growing plants, as well as making fine humus.
Avoid crabgrass and grass full of seed heads. Also, do not use clippings from lawns which have been treated that season with herbicide or a fertilizer/herbicide combination. Grass clippings may be used directly as mulch around vegetables or fruit plants, or they may be composted. They are an excellent source of nitrogen to heat up a compost pile, especially for those gardeners without access to manures.
A layer of leaves, 2 to 3 inches thick after compaction, provides good annual weed control. Leaves will decompose fairly quickly, are usually easy to obtain, attractive as a mulch, and will improve the soil once decomposed. To reduce blowing of dry leaves, allow to decompose partially. Leaves are a highly recommended vegetable gardening mulch.
Note: Leaves of the black walnut tree (Juglans nigra) are an exception due to the presence of juglone, a chemical that inhibits growth of many plants. While walnut roots and hulls cause most of the problems, the leaves also contain smaller quantities. Avoid using leaves collected from under black walnut trees as garden mulch. However, if leaves are obtained from a municipal collection source, the quantity of black walnut leaves likely will be diluted sufficiently that no injury should be observed. Several other nut trees also produce small quantities of juglone, and problems with sensitive plants are seldom seen even when growing under those tree canopies.
A 2- to 3-inch layer of compost is a fair weed control. Most compost, however, provides a good site for weed seeds to grow. It is probably better used by incorporating it into the soil since it is an excellent soil amendment. A layer of compost may be used on overwintering beds of perennials, such as asparagus or berries, to provide nutrients and help protect crowns.
Bark and Wood Chips
A 2- to 3-inch layer of bark provides good weed control. Wood chips are slower to decay than shredded bark, and can be used as a pathway material in raised beds.
Inorganic Mulches for the Vegetable Garden
Inorganic mulches are made from man-made materials such as black plastic or newspaper.
One layer of black plastic provides excellent weed control. It is relatively slow to decompose, but will be somewhat broken down by sunlight and must be replaced every two years at least. Black plastic mulch will increase the soil temperature by about 8°F in the spring. It may cause soil temperatures to rise too much in mid-summer, damaging the roots of plants unless a good foliage cover or organic mulch prevents direct absorption of sunlight.
Check periodically to see that soil remains moist beneath the plastic; cut holes in it if water doesn’t seem to be getting through. Black plastic is easy to obtain, but is fairly expensive. A new type of black plastic has recently come onto the market which has a white, reflective side to prevent the overheating problems experienced with solid black plastic. Another plastic is porous to allow penetration of water and exchange of gases between the soil and air.
Using 2 to 4 layers of newspaper provides good weed control. It decomposes within a season and is readily available and cheap. Cover with an organic mulch, such as sawdust or hay, to hold paper in place. Excellent for use in pathways and around newly set strawberry plants.
Lead in printers’ ink has been a concern of some vegetable gardeners desiring to use newspaper, however, printers no longer use lead compounds in ink for black and white newsprint, though colored inks may contain lead.