Muskmelons, tomatoes, peppers, cucumbers, squash, eggplant, watermelons, pumpkins, and okra are vegetable crops that have shown significant increases in earliness, yield, and fruit quality when grown on plastic mulch. Some less valuable crops such as sweet corn, snap beans, and southern peas have shown similar responses. Some of the advantages and disadvantages of using plastic mulches are outlined below. (For additional information, see AG-489, Plasticulture for Commercial Vegetables.)

1. Regulation of soil temperature: At a 2 inch depth; 4 to 9°F increase under black mulch, or 8 to 10°F increase under clear mulch. White-on-black plastic may reduce soil temperature by 5 to 20°F. Silver plastic may reduce the temperature by 6°F
2. Reduced soil compaction: Soil under plastic mulch remains loose, friable and well-aerated. Roots have access to adequate oxygen and microbial activity is excellent.
3. Reduced fertilizer leaching: Water runs off the impervious mulch, resulting in maximum utilization of the fertilizer.
4. Reduced drowning of crops: Water is shed from the row area and excess water runs off the field thus reducing drowning and other excess soil water stresses.
5. Reduced evaporation: Soil water does not escape from under plastic mulch. Plant growth on mulch is often at least twice that on bare soil. The resulting larger plants will require more water, so mulching is NOT a substitute for irrigation.
6. Cleaner product: A mulched crop is cleaner and less subject to rots due to elimination of soil splashing on the plants or fruits. Note: Beds should be firm and tapered away from the row center. Plastic should be tight to promote run-off. There should be no puddles on the mulched beds!
7. Root pruning eliminated: Cultivation is not necessary except for the area between the mulched strips. Therefore, roots are not pruned.
8. Reduced weed problems: Black, white-on-black, silver, and other dark colored plastic mulches provide good weed control in the row. Clear plastic will require use of a herbicide, fumigation or lifting the mulch and cultivating. Often, weeds between mulch strips can be controlled by a herbicide.
9. Earlier crops: Black plastic mulch can result in 2 to 14 days earlier harvest while clear plastic can result in a 21-day earlier harvest.
10. Increased growth: Plastic mulch is practically impervious to carbon dioxide (CO₂), a gas that is of prime importance in photosynthesis. Very high levels of CO₂ build up under the plastic, because the film does not allow it to escape. It has to come through the holes made in the plastic for the plants and a "chimney effect" is created, resulting in localized concentrations of abundant CO₂ for the actively growing leaves.
11. Cooling for late season crops: White-on-black plastic mulch can allow for good production in the heat of summer. It is now common practice for farmers to plant tomatoes, peppers, and eggplants on white-on-black plastic.

1. Costly to remove: Plastic mulch and drip irrigation tube must be removed from the field annually. Plastic does not break down and should never be disked or tilled into the soil. Photo- and bio-degradable plastics hold promise.
2. Greater initial costs: Plastic mulch and drip irrigation will increase cost of production. These costs should be offset by increased income due to earlier harvests, better quality fruit and higher yields.
3. Increased management: Plastic mulch and drip irrigation must be carefully monitored (daily) to be successful.
4. Increased soil erosion: Soil erosion may increase in the middles between plastic strips.
5. Weeds near base of plants: Weeds can grow out of the holes in close proximity with crops and if they grow more rapidly than the crop plant, may need to be removed by hand.

The first step is to take two soil samples in early fall. Have one sample assayed for mineral content and one for nematodes. If the soil test suggests applying lime, apply enough in the fall to reach pH 6.0 to 6.5 using dolomitic lime if magnesium is low. If there is a nematode problem, fumigate the soil at the time the plastic mulch is being laid. By using a multipurpose fumigant, you can get good control of weeds, nematodes and soil-borne diseases. The soil should be free of debris and in good physical condition prior to preparing the beds for fumigation.

Using the soil test report as a guide, apply fertilizer during bed preparation. Consult Horticultural Information Leaflets and the Southeastern US Vegetable Crop Handbook for specific crop recommendations. Amounts to be sidedressed need to be included in the total fertilizer requirements.

Caution: Using fertilizers with ammoniacal N in fumigated soils can result in ammonium toxicity to the crop. Normally, at least 50% of the nitrogen (N) should be in the nitrate (NO₃) form. Gardeners can use calcium nitrate (15.5-0-0), sodium nitrate (16-0-0) or ammonium nitrate (33.5-0-0) as a nitrate sidedress source.

When using drip irrigation with plastic mulch, one half of the N and K and all of the P should be incorporated at bedding. The remaining N and K should be applied through the drip tube using soluble fertilizers (e.g. calcium nitrate, sodium nitrate, 20-20-20, 15-0-14, or potassium nitrate). Gardeners can make a small hole about 6 inches from the plant in the plastic and apply ¹⁄₄ cup of fertilizer. The entire amount of fertilizer may be incorporated in the bed but utilization by plants might be less efficient than with fertigation.

Bedding machines available to growers include single and multiple row models. With some bedding machines, the soil is lifted and then bedded in one operation. With others, the soil is first lifted in one operation with hilling disks or double disk hillers on a tool bar and then compressed to a uniform height and density using a bed press pan. Gardeners should use raised beds. Note: Be sure that enough soil is pulled up so that the bed has good sharp corners. Bedded rows should be spaced on 5- or 6-ft centers depending on the equipment. A bed with a 30 inch top should slope from the center to the edge with a drop of 1.25 inches, allowing excess rainfall to run off the mulch.

The plastic mulch is generally 4 or 5 feet wide, 1.25 to 1.50 mil thick, embossed (diamond-shaped design on film, which helps hold mulch tight against the soil) or slick, and comes in 2,400 ft rolls.

For single-row crops such as tomatoes, cucumbers, muskmelons, honeydews, watermelons, and pumpkins, the drip tube should be placed 4 to 5 inches from the center of the bed and 1 to 2 inches deep with the emitters facing upward. There are 1,000 to 7,500 feet of drip tube on a roll depending on the brand. For double row crops like summer squash, okra, eggplant, peppers, beans, peas, lettuce, and sweet corn, the drip tube should be placed directly on the center of the bed and buried 2 to 3 inches deep. For 5 foot row centers there are 8,712 linear ft of row per acre, so a grower would require about 3.5 rolls of plastic mulch per acre. For 6-ft centers, 3 rolls of plastic mulch will be required per acre.

Commercial growers: Take time to adjust the bedding machine so that the press wheels hold the plastic firmly against the bed and the disks place soil halfway up the side of the bed but not on top of the bed. Also, anchor the plastic and drip tube when starting applications, covering it with soil and standing on the drip tube.

Home gardeners: Take time to adjust the plastic so that it is held firmly against the bed and soil is placed halfway up the side of the bed but not on top of the bed. Also, anchor the plastic and drip tube when starting applications. Covering them with soil by digging a trench perpendicular to the row direction and putting soil on top provides a good anchor.

Most farmers and gardeners lay plastic mulch and drip tube in early spring. The soil should be moist but not so wet that a good, solid bed can be created. Applying the mulch in the spring helps ensure the plastic is intact and in good condition when the crop is planted

Laying the plastic mulch and drip tube plus fumigating in the fall, however, also has several advantages:

1. Wet weather conditions are prevalent in the spring and can result in delays in laying the plastic and in transplanting.
2. Better soil fumigation is possible in the fall because the soil is not apt to be too wet or too cold.
3. Nematode populations should be the highest in the fall and maximum eradication is possible at that time.
4. Fall applied mulch often makes it possible to transplant 10 to 14 days earlier in the spring.

The disadvantage of fall application is that the plastic may be damaged over the winter due to wildlife puncturing the plastic as they walk through the field, wind getting under the plastic and pulling it up in sections. and other weather related damage occuring.

The amount of fumigant actually applied per acre will depend on row width and will be a percentage of the broadcast rate (Consult the NC Agricultural Chemicals Manual). Air temperature should be at least 50°F and the soil should be well worked, free of undecomposed plant debris and have adequate moisture for seed germination. If both the air and soil are warm most fumigants should escape through the plastic mulch within 12 to 14 days.

Weed Control - For information on weed control under clear plastic mulch and in the row middles between black, white-on-black, silver, or other colored plastic mulch consult the Southeastern US Vegetable Production Handbook, the North Carolina Agricultural Chemicals Manual, or your local N.C. Cooperative Extension center. Only approved herbicides can be used between rows of plastic, because this is not a fallow area.

Insect and Disease Control - Good insect and disease control is essential. Consult the Southeastern US Vegetable Production Handbook, the North Carolina Agricultural Chemicals Manual, or your local N.C. Cooperative Extension center.

For extra earliness in peppers and tomatoes, large containers (cell sizes 3 to 4 inches) should be used. For the other vegetable crops use 1 to 2 inch cell sizes. Commercial transplants can be set by hand or machine; gardener transplants can be set by punching a hole in the plastic and placing the plant in the hole. When transplanting by hand, several tools can be used to make holes in the plastic such as a long handled bulb setter or a sturdy can or cylinder welded onto the end of a handle. The hole should be 2 to 4 inches wide and deep enough for the plants to be transplanted. A hand tobacco plant setter or long handled bulb-setter works well once the holes are made in the plastic mulch. With both hand setting and machine setting, the use of a "starter solution", a soluble fertilizer high in phosphorous (P) will often get the plants off to a good start. Examples are 12-52-12, 10-20-10, or 12-48-8.

Drip irrigation is recommended for use with plastic mulches although other types can be used successfully. The frequency of irrigation will depend on soil type and stage of crop growth. Irrometers and electronic sensors at the 6 inch and 12 inch depth in the mulched bed are recommended as an aid in determining irrigation needs. Frequent probing with a soil tube near the plant row will also help to keep a check on soil moisture. Normally the area around the drip tube is very soft to the touch and the side of the row away from the tube should be only slightly soft. For more detailed information on trickle/drip irrigation consult the Southeastern US Vegetable Handbook, your local N.C. Cooperative Extension center, or a drip-irrigation expert. DO NOT USE PLASTIC MULCH WITHOUT IRRIGATION.

Once the first crop has been harvested, it is recommended that a second crop be grown on the mulch (See Table 1). This "intensive cropping" results in two acres of production from each acre of actual land. The second crop can be fertilized (1) through the drip tube using soluble fertilizers and a fertilizer injector, (2) through overhead fertigation, or (3) by placing fertilizer in holes in the plastic between plants. Consult HIL-33C for additional information on injecting fertilizers through the drip line.

NEVER plant a field or bed to the same crop twice in one year! Suggested spring-fall sequences are listed in Table 1 below.

Commercial growers -- An herbicide can be used to terminate the first crop. Note: Take care to avoid damaging the trickle/drip tube when planting the second crop.

Home gardeners -- Simply pull out the first crop and plant the second in holes appropriately spaced for the crop. Note: Take care to avoid damaging the trickle/drip tube when planting the second crop.

If wind damage is a concern, trips of rye can be established to protect vegetable seedlings from prevailing winds. Each rye field strip should be the width of a typical grain drill (8 to 10 feet) (gardens should be 4 to 6 feet wide or 6 to 8 rows) and far enough apart to plant 5 or 6 rows of vegetable seedlings. Well-grown rye strips planted in the fall will promote earliness and provide protection for the young transplants. Spring topdressing in February will help assure a good thick rye stand.

When laying plastic in the spring, plant the entire field or garden with rye, but be sure to work up the crop area early enough in the spring to minimize crop debris interference with fumigating and plastic laying. Once wind protection is no longer required, mow the rye and use this area as a drive row for spraying and harvesting. Commercial growers use this drive row for a boom sprayer that covers 2.5 or 3 rows on either side of the drive. An airblast sprayer can also be used.

The use of plastic mulch and drip irrigation is a common practice among conventional and organic vegetable farmers across the nation. The benefits are great but the disposal problem is concerning. Many alternatives are currently being tested including a variety of paper mulches and biofilms made from hemp.