Black plastic sheeting used as garden mulch has its share of problems. Removing and disposing of large quantities of black mulch can be difficult. In larger scale growing, costly special equipment is needed to work with black mulch, while in the home garden, extra care must be taken with watering and fertilizing routines. Black plastic can also interfere with soil development, and unlike organic material mulches like compost and straw, does not add beneficial nutrients.
Removal and Disposal
Non-degradable black mulch must be removed from the fields and disposed of each year. Most of this labor must be done by hand. According to the Oklahoma Extension Service, it takes approximately 8 hours of hand labor to remove the black mulch from each acre.
Most commercially available black mulch can not be composted or recycled, so disposal involves paying a solid waste fee to commercial garbage haulers or a municipal transfer station. Depending on the quantity of black mulch involved, purchase and disposal costs of black mulch can run a few hundred dollars per acre.
Special Equipment and Techniques
Black plastic mulch must be pressed tightly and evenly to the soil, without pockets of air underneath. Commercial growers covering several acres need to use expensive plastic-rolling machinery to lay the mulch out and then to cut it evenly for planting. The equipment can be cost-prohibitive for many small growers, though some resolve this by purchasing the machines cooperatively amongst several market farmers.
Watering over the mulch results in most of the water running off or evaporating, so commercial growers must install drip lines under the plastic. Gardeners or small growers must otherwise water each plant individually at the base of its main stem where it goes through the black plastic. The cost, time, and labor required by these watering techniques may offset any advantages gained in weed reduction by using the black mulch.
Soil Improvement and Fertilizer
Black mulch does not add any nutrients to the soil. All soil amendments in black mulch growing areas must be done before the mulch is installed, and those amendments must be carefully planned to ensure that they last the entire growing season. Although liquid-soluble fertilizer can be added to irrigation drip lines or used in hand-watering black-mulch grown crops, other soil amendments like lime or minerals cannot be incorporated into the growing medium until the black mulch is again removed.
Fertilizers rich in trace nutrients, like fish emulsion or compost tea, make require extra dilution and filtration steps before they can work in a drip line system as they tend to contain particles that can clog the lines. This makes fertilizing the plants, especially for organic growing systems, more difficult.