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Synthetic mulch

Many synthetic mulch materials are marketed for use in gardens, including plastic films of various colors, spun materials that are permeable to water, and plain and oiled paper. In addition, some gardeners use newspapers, cardboard, old carpeting and other materials as weed barriers. All of these can be effective, but they all pose certain problems as well.

Weeds along edges

All synthetic mulches must be anchored along all edges to prevent the material from blowing in the wind. Usually this is accomplished by piling soil along the edge of the mulch material. This soil is, of course, above the mulch and so tends to become weed infested. Since these weeds cannot be hoed without damaging or uncovering the mulch, much hand weeding may be required to prevent seed production by annuals and vegetative propagation of perennials. Weeds also tend to grow thickly in the holes made for the crop, again requiring hand weeding.

Irrigation & mulch

Some, synthetic mulches like plastic film, cardboard and oiled paper are impermeable to water. Usually they are most effective if a drip irrigation system can be placed under the mulch.

Disposal

Most synthetic mulches pose significant end-of-seasop disposal problems. The labor and cost of disposing of large amounts of dirty and possibly wet mulch material at the end of the growing season should be considered when contemplating the use of these materials. Newspaper, brown kraft paper and kraft paper treated with vegetable oil are all biodegradable, but unless gathered, chopped up and composted, they may leave the garden unsightly through the winter.

Spun ground covers

Spun cloth ground covers similar to floating row covers but colored brown or black to block light from weeds are reasonably effective for preventing the growth of annual weeds. Many perennials, however, can penetrate these materials. Pulling these weeds pulls on the cloth, and that may disturb crops planted in holes in the material. Moreover, great masses of quackgrass and other perennials may cling to these ground covers when they are collected, thereby greatly increasing the expense of disposal. If perennial grasses are present, plan on several large garbage cans of debris per roll of ground cover.

Old carpeting

Old carpeting is very effective at blocking the growth of even vigorous perennials for several years, but it cannot be recommended for use in vegetable gardens due to the toxic compounds (e.g., formaldehyde) that are released as the carpeting weathers. Depending on one's outlook, this may seem less of a problem in beds of ornamentals. After a few years however, weeds will establish in dust and decayed organic debris that collects on the surface of the carpet. These plants will grow through the decaying fabric and effectively anchor to the soil what has then become a large piece of ugly debris.

Conclusions

Although plastic mulches are effective for producing early crops (e.g., of tomatoes), in general, synthetic mulch materials tend to be more trouble than they are worth for weed control. The one exception is that paper mulches laid under straw, compost or other organic materials can increase the effectiveness of the natural mulch, and may decay sufficiently by the end of the season to avoid disposal problems.