Plastic mulch is generally 0.75–1.25 mils thick, 4–6 feet wide, in rolls 1,000–4,000 feet long. Selecting the right mulch and installing it properly is essential for maximizing its benefits. Plastic mulches are available in several colors, but black is the most widely used, especially in temperate climates. The color of plastic mulch affects soil temperature and weed suppression.
Table 17: Plastic Mulch Types and Characteristics
| MULCH COLOR | SOIL TEMPERATURE CHANGE | WEED CONTROL | RELATIVE PRICE | KEY PROPERTIES |
|---|---|---|---|---|
| Black | +3–5°F | Good | $ |
|
| Clear | +8–14°F | Poor | $ |
|
| White-on-black | -2°F | Good | $$ |
|
| Silver/metallic | -2°F | Good | $$ |
|
| Infrared Transmitting | +4–6°F | Good | $$ |
|
Red, blue, green, or yellow mulches are used as they produce distinct radiation that reflects into the crop canopy. However, research has shown inconsistent results from colored mulches, and they are not widely used in commercial production except for green mulches in California strawberry production.
Apply plastic mulch after fields have been leveled and smoothed and fertilizer has been applied, and when there is good soil moisture (at or near field capacity, which is the amount of moisture left after a rain or irrigation event after surplus water has moved out of the root zone by gravity). When using black mulch, good uniform soil contact is essential, as the soil is warmed by heat conduction. Commercially, the simplest way to apply mulch film is with a mechanical mulch layer. Plastic mulch can be laid flat against the ground or on raised beds. Raised beds offer additional soil drainage and early warming. Hand application is an option, but applying more than a half-acre can be difficult and time consuming.
Generally, plastic mulch is laid in the spring as soon as the land can be prepared. However, some spring seasons are wet and can delay normal land preparation and planting activities. An alternative is to lay plastic in the fall. Fall mulch application will require similar land preparation as in the spring, but use of a cover crop between the rows is recommended to prevent soil erosion. Oats will winter-kill, but winter rye will need to be terminated by using an herbicide (such as Roundup or Gramoxone), or by mowing and cultivation.
After harvest, traditional polyethylene (PE) mulches should be removed from the field and disposed of properly according to local ordinances and available waste-management options. Recycling of used PE mulch remains difficult because the mulch is often heavily contaminated with soil and plant debris, which can make up a large fraction of the recovered material by weight. As a result, relatively little agricultural mulch film is recycled, and much of it is landfilled or stockpiled. Incomplete retrieval can also leave persistent plastic residues in soil.
Biodegradable Plastic Mulch
Some early products marketed as "biodegradable" were photodegradable or oxo-degradable materials that fragmented under sunlight but did not reliably achieve complete biodegradation in agricultural soil. Current soil-biodegradable plastic mulches (BDMs) are different; they are designed to be tilled into the soil after their service life, and under aerobic conditions, soil microorganisms convert the material into carbon dioxide, water, and microbial biomass.
The term “biodegradable” is often misunderstood. A mulch may biodegrade in one environment, such as industrial compost, but not adequately biodegrade in agricultural soil. For that reason, biodegradability claims should identify the disposal environment and the standard used to support the claim. Commercial BDMs are typically engineered blends of biodegradable polymers, often including starch-based materials and biodegradable polyesters. Their field performance and degradation rate depend on product formulation, thickness, soil conditions, temperature, moisture, and management after incorporation.
The most recent research shows that BDMs generally provide weed suppression, soil warming, moisture conservation, and crop yield benefits comparable to PE mulch in many specialty crop systems, although performance varies by crop, season length, product, and local climate. Multi-year studies have generally reported limited or transient effects on soil physical, chemical, and biological indicators under tested conditions. However, degradation is strongly site- and product-dependent, and measurable residues can persist for multiple seasons after incorporation. Repeated-use studies suggest that reaching 90% degradation may take roughly 21–58 months, depending on product and field conditions, with slower degradation expected in cooler or drier soils.
As BDMs deteriorate, visible fragments may disappear before complete mineralization occurs. In some cases, macrofragments break down into smaller fragments before full biodegradation. For this reason, the disappearance of visible mulch should not be interpreted as proof of complete biodegradation.
Although the USDA National Organic Program added “biodegradable biobased mulch film” to the National List in 2014, no commercially available soil-biodegradable or compostable plastic mulch is currently allowed for use in U.S. certified organic production. Current products do not meet some of the National Organic Program requirements. Growers should confirm acceptability with their certifier before using any mulch product marketed as “organic.”
Biodegradable mulches initially cost about two times more than standard black PE mulch, but end-of-season labor and disposal costs are avoided. Cost-effectiveness depends on seasonal labor, disposal fees, and mulch price.
Biodegradable mulch is thinner (0.5–0.8 mil) than typical black PE mulch (1–1.25 mil), and extra care is required to prevent tears when laying it. When laying biodegradable mulch, do not stretch as tightly as you normally would with polyethylene mulch, as it breaks down more quickly when stretched. Applying in early morning when temperatures are cooler can help. Apply right before planting because the mulch will start to break down as soon as it makes soil contact. Buy what you need each year—do not try to store biodegradable mulch. The mulch can start to break down in storage, particularly if storage conditions are moist and/or warm.
BDMs should be incorporated into the soil soon after harvest, and incorporation should promote good soil-mulch contact in the biologically active tilled zone. Degradation is generally faster in warm, moist, well-aerated soil and slower when fragments remain on the surface, are buried too deeply, or soils stay cold or dry.
Paper mulch is another option, and is most commonly used in organic systems. It can suppress weeds and biodegrade in the field, but it generally has a shorter service life than plastic mulches, can tear during installation, and may lose effectiveness quickly in wet or windy conditions or when mechanically disturbed.
Before purchasing, verify that a product meets soil-biodegradability standards or certification requirements appropriate for agricultural soil. EN 17033 and ISO 23517 are the most relevant current product-level frameworks for soil-biodegradable mulch films. Laboratory methods commonly used to assess soil biodegradation include ISO 17556 and ASTM D5988. ASTM D6400 and ASTM D5338 are composting standards and should not be used alone to support soil-biodegradability claims for field incorporation.