Commercial Vegetable Cooperative Extension Service College of and Production With Home Economics

Guide H-245

George W. Dickerson, Extension Horticulture Specialist This publication is scheduled to be updated and reissued 12/07.

In New Mexico, growing vegetables commercially, yields. Black plastic can accelerate crop whether for vegetable sheds or farmers’ markets, re- production as much as one to two weeks. Clear quires intensive management and marketing skills. plastic mulch has been shown to increase earli- Success involves properly managing scarce ness as much as three weeks in northern cli- supplies, controlling and other pests and sup- mates. growth, however, can be a major plying a high-quality product when the price is high. problem under clear plastic unless appropriate High prices generally are associated with limited sup- or fumigants are used. Selecting the ply and high demand. crop type (vine crops like pumpkins, squash, melons) also is important in warmer areas of Mulches the state for good ground cover or shading in the summer to prevent excessive heat build up un- Mulching is an agricultural cropping technique that der the plastic. involves placing organic or synthetic materials on the ¥ Reduced evaporation. Plastic mulches help re- soil around plants to provide a more favorable envi- duce evaporation of moisture from the soil. Irri- ronment for growth and production. Organic mulches gation frequency and amounts generally can be traditionally are used in backyard gardens and smaller reduced, although additional water may be truck gardening operations, since materials may be needed to support earlier and greater crop pro- limited and application techniques are labor intensive. duction. A more uniform soil moisture also will Organic mulches provide many of the benefits of result in less plant stress. most synthetic mulches, except soil warming and pe- ¥ Weed control. Since black plastic mulch pre- rennial weed control. Unlike synthetic mulches, how- vents light from reaching the soil, growth of an- ever, organic mulches like hay, straw, grass clippings, nual and most perennial weeds can be pre- and compost tend to return nutrients to the soil vented. Thin black plastic mulch will not, through decomposition. however, control nutsedge. Inorganic plastic mulches have been used by com- ¥ Improved quality. Plastic mulches help prevent mercial growers since the early 1960s, with black fruit crops from touching the soil. This reduces and clear being the most popular. Tomatoes, the incidence of fruit rots and keeps fruit peppers, eggplants, vine crops and okra generally cleaner. respond well to these plastics. Plastic mulches nor- ¥ Reduced soil compaction and root pruning. mally are used in conjunction with drip to Better weed control results in less cultivation maintain optimum soil moisture and for improved and less root pruning. Undisturbed beds also re- stand establishment. main more friable with less compaction. Weeds between beds can be controlled with directed Advantages of Plastic Mulch (Lamont, 1991) herbicides or by mechanical means. ¥ Reduction in fertilizer losses. Flood and fur- ¥ Earliness and greater yields. Earlier plant row irrigation techniques tend to leach nitrogen growth and earlier crop production are two of and other water soluble nutrients below the root the primary benefits of using black and clear zone. Since plastic mulch techniques generally plastic mulches. Earlier crop production gener- include , nutrient loss is kept to a ally results in higher market prices and higher minimum. Nutrients can be injected into the drip

To find more resources for your business, home, or family, visit the College of Agriculture and Home Economics on the World Wide Web at aces.nmsu.edu system and accurately delivered to the root zone and expansion of the mulch. Also, it generally is more as needed. resistant to wind fatigue and cracking. Plastics come ¥ Insect control. In some cases, reflective silver in rolls 2,000 to 4,800 feet long (depending on the and white plastic mulches help repel aphids and thickness) and are 3 to 5 feet wide. other insects that damage plants and are vectors Woven, black mulches have been of viral diseases. used in the and nursery industries for some time as weed barriers. These ultraviolet, light- Disadvantages of Plastic Mulch stabilized mulches are guaranteed to last up to five years. They allow water and air penetration while ¥ Removal and disposal. Removing the plastic controlling weeds. These tear-resistant mulches (16 mulch after the cropping season is the biggest mil thick) can be reused year after year. In experi- disadvantage. Although removal equipment is ments with small vegetable producers in northern available, plastic tends to become brittle in New New Mexico, these mulches have been used to warm Mexico’s intense sunlight, making it difficult to the soil, control weeds, harvest rainfall and reduce remove in one piece. The “tucks,” or sides of evaporation of moisture from the soil. the mulch buried in the dirt, remain intact, since they are not exposed to the sunlight and separate Mulch Colors from the brittle mulch on the bed top. Little pieces of plastic can scatter across a field. Many A mulch’s color affects the temperatures below landfills also will not accept plastic, and it is and above the mulch through the absorption, trans- difficult to recycle. Photodegradable and biode- mission and reflection of solar energy. This affects gradable mulches have been evaluated, but re- the microenvironment surrounding the plants. The sults have been mixed. Another alternative is degree of contact (thermal contact resistance) be- woven, black polypropylene mulch with an ul- tween the mulch and the soil also affects soil warm- traviolet light inhibitor that can be reused for ing. The better contact the mulch has with the soil, many seasons. the more effective the warming properties of the ¥ Cost. The cost of applying plastic mulch can mulch (Lamont, 1999). be quite high both in terms of materials and ¥ Black. Black plastic mulch is the most popular equipment. The minimum equipment required color used in commercial vegetable production, includes bed-shaping equipment and a mulch especially for weed control. As a blackbody ab- applicator. Other equipment may include a sorber, this plastic absorbs most incident solar drip-line applicator (usually associated with radiation, including visible, infrared and ultra- the mulch application) and a transplanter or violet light. Much of the thermal energy, how- seed planter. The advantages of using a mulch ever, is lost to the atmosphere through convec- for earliness, increased yields, reduced water tion and reradiation. Transferring of thermal application, better weed control and higher energy to the soil can be optimized by maximiz- prices must offset the increased cost of using ing mulch contact with the soil. Soil tempera- plastic mulches. tures under black plastic during the daytime can ¥ Management. With drip irrigation, managing be as much as 5¼F higher at a 2-inch depth and plastic mulch is more intense. Wilting plants 3¼F higher at a 4-inch depth than bare soil at the could mean a plugged drip line, while overly same depths (Lamont, 1999). wet areas could mean rodent damage to the ¥ Clear. Soil temperatures during the daytime un- lines. Drip line problems are hard to evaluate der clear plastic can reach 8-14¼F higher at the when covered with mulch. 2-inch depth and 6-14¼F higher at the 4-inch depth than bare soil at the same depths due to a Types of Plastic Mulch greater (85 to 95%) solar radiation transmit- tance. Clear plastic absorbs very little solar ra- Most commercial plastic mulches are made of ei- diation. Water droplets that condense on the ther linear, low-density or high-density underside of clear plastic allow solar light polyethylene. High-density polyethylene is lighter and (short-wave radiation) in, but block outgoing, stronger than the same thickness of low-density poly- long-wave infrared radiation (heat). This heat ethylene. Most plastic mulches vary in thickness from normally is lost to the atmosphere from bare 0.75 to 1.5 mil and may be smooth or embossed soil. Incoming solar radiation, however, makes (McCraw and Motes, 1991). The diamond-shaped weeds a major problem under clear plastic un- pattern on embossed plastics helps reduce contraction less controlled with a or fumigant

Guide H-245 ¥ Page 2 (Lamont, 1999). Solarizing or disinfecting of exhibit improved soil-warming characteristics, the soil has been used in some areas of the although generally not as well as clear plastic. country to reduce soilborne diseases and some Colors range from blue-green to brown weeds. To achieve sufficiently high tempera- (Lamont, 1999). tures for solarization, the soil must remain cov- ered for several weeks during the hot part of the Soil Preparation and Preplant Fertilization summer. Good soil moisture will improve ther- mal conduction of heat into the soil profile The soil should be deep plowed or disked at least (Katan, 1980). one month before bed preparation. Incorporate crop ¥ White. Light is reflected back into the atmo- residues well. Remove all trash, rocks or clods from sphere or the plant canopy from a white plastic the field that may hinder the application of the plastic. mulch, resulting in slightly cooler (-2¼F at Preplant fertilizers can be broadcast and incorporated 1-inch depth) soil temperatures. White plastic into the beds as they are formed. Good soil moisture mulches can be used to establish crops in the (60 to 80% of field capacity) is necessary to make summer, when a reduced soil temperature might firm, smooth beds (Granberry, Kelley, Chance, be beneficial. Coextruded white on black plastic McLaurin, Harrison, Sanders, 1994). It is important mulch helps cool the soil (white) while control- that the bed be firm, so the soil doesn’t settle. ling weeds (black) (Lamont, 1999). The light reflected back into the plant canopy with white Plastic Mulch and Drip Irrigation mulches also can be helpful for some green- Line Application house crops that have limited light. ¥ Silver/aluminum. Reflective silver or alumi- Plastic mulchs can be applied by hand in smaller num mulches also give cooler soil temperatures. operations or by machine in larger ones. The basic They tend to repel aphids, which can serve as technique involves bedding up the soil, shaping and vectors for various viral diseases (Lamont, pressing the bed and applying the plastic mulch and Sorensen and Averre, 1990). drip irrigation line. These operations can be per- ¥ Red. Red plastic mulch has been shown to in- formed separately or in various combinations. crease tomato yields and quality in some trials First, beds are raised with hilling discs and then and reduce the severity of early blight in others. compressed to a uniform height and density with a It also has been shown to increase yields of hon- bed shaper. Beds normally have 5- to 6-foot centers eydews, muskmelons and zucchini. In addition, and generally are 4 to 6 inches high and 30 to 34 inches it has been shown to significantly increase soil wide, sloping slightly (1.25 inches) from the center to temperatures (Lamont, 1999). Not all red colors the edges to shed excess rainfall (Lamont, 1991). are the same, however, and results have not Mulch applicators generally include a mulch dis- been consistent. penser that holds at least one roll of plastic, small ¥ Other colors. Yellow, orange, blue and gray discs at the bed edges to clean out or open the fur- plastic mulches also have been evaluated. The rows, rubber inflatable tires that press the edges of different radiation patterns that are reflected the mulch into the furrows, and discs that cover the back into the canopies of various crops from edges (tucks) of the mulch with soil to keep it in these mulches affect plant growth and develop- place. The plastic must be kept taut to ensure good ment in different ways. Some colors like yellow contact with the soil. Drip line and fumigant applica- attract certain insects like green pea aphids tors usually are located in front of the mulch applica- and cucumber beetles (Lamont, 1999). Such tor. Newer machines may combine bed formation mulches might be used in a field to grow “catch and mulch application. crops” to pull insects away from other crops. The drip line can be installed on the soil surface Blue-colored mulches have been shown to in- under the mulch or 2 to 3 inches below the soil sur- crease zucchini and honeydew yields. More re- face. The emitters should face up to reduce plugging. search needs to be conducted to determine the For most crops like tomatoes, chile and vine crops effects of these colors on plant growth, yields, planted one row per bed, the drip line should be lo- earliness and pest resistance. cated 4 to 8 inches to the side of the crop and 1 to 2 ¥ Wavelength-selective mulches. These mulches inches deep. The crop should be planted in the middle selectively absorb photosynthetically active ra- of the bed. Transplants or direct-seeded vegetables diation (PAR), while transmitting solar infrared can be planted directly through the plastic with a ma- radiation. Also called infrared-transmitting chine or by hand. Starter fertilizer solutions generally (IRT) mulches, they help control weeds and are applied to transplants to promote early growth.

Guide H-245 ¥ Page 3 Fertilize plants midseason by injecting appropriate LITERATURE CITED soluble fertilizers through the drip line. Dickerson, G.W. 2000. Evaluation of an integrated Removal of Plastic limited irrigation water catchnet system for veg- etable production. Cooperative Extension Service, The plastic must be removed after the growing sea- New Mexico State University, Las Cruces, N.M. son. Do not disc plastic under. Machines are available Circular 568. commercially for plastic removal, but they can be ex- Granberry, Darbie M., Kelley, William Terry, Chance, pensive. In most cases, the plastic must be removed Willie O., McLaurin, Wayne, Harrison, Kerry A., by hand and disposed of in a landfill. and Sanders, Doug. 1994. for commer- cial vegetable production. Cooperative Extension Water Harvesting Service, University of Georgia. Bulletin 1108. Katan, J. 1980. Lutte contre les maladies du Sol a Most impermeable plastic mulches are applied on a llaide d’um paillis de polyethylene. Plasticulture slight slope from the middle of the bed to the edge to 46:2-6. shed rainfall and prevent flooding. This also keeps Lamont, W. J. 1999. The use of different colored water from accumulating around melons or other vine mulches for yield and earliness. Proceedings of the crops and causing fruit rot and cracking, which is New England Vegetable and Berry Growers Confer- rarely a problem in the desert Southwest. Ideally, ence and Trade Show, Sturbridge, Mass. p. 299-302. rainfall should be used to supplement irrigation water. Lamont, W. J. 1991 (April). Drip irrigation: Part of a Woven, black polypropylene mulch has been used complete vegetable production package. Irrigation experimentally by NMSU’s Cooperative Extension Journal (reprint). Service specialists to harvest rainfall to produce crops Lamont, W. J., Sorensen, K.A., and Averre, C.W. like tomatoes, chile, cantaloupes, pumpkins and 1990. Painting aluminum strips on black plastic squash, and to reduce the need for supplemental irri- mulch reduces mosaic symptoms on summer gation (Dickerson, 2000). One such technique in- squash. HortScience 25:1305. volves securing a 4-foot wide piece of woven plastic McCraw, D. and Motes, J. E. 1991. Use of plastic across a level field with 6-inch fabric pins along the mulch and row covers in vegetable production. edges and then building borders on the edges to chan- Cooperative Extension Service. Oklahoma State nel irrigation water down the plastic. The plastic helps University. OSU Extension Facts F-6034. reduce water evaporation from the soil and helps har- vest rainfall, which seeps through the plastic prevent- ing it from accumulating around fruit. Direct-seeded or transplant crops are planted through holes burned through the middle of the plastic with a propane torch or round branding iron. Fabric pins placed through the plastic near the holes keep the plastic in place and prevent plant abrasions. The plas- tic not only helps to conserve and harvest moisture, but also to control bindweed and other weeds and warm the soil, resulting in earlier crops. An ultraviolet light inhibitor incorporated into the plastic makes it reusable, eliminating disposal problems associated with traditional plastic. Its higher cost can be depreci- ated over its longer life span.

New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of Agriculture cooperating. December 2002 Las Cruces, NM 3C

Guide H-245 ¥ Page 4