How can I grow strawberries using plasticulture?
Answer: The term plasticulture refers to the practice of using plastic materials in agricultural applications, most often as a plastic plant or soil covering. Organic and conventional growers in California and Florida, where most of the nation’s strawberries are produced, tend to favor plasticulture growing systems. They grow plants as annuals, transplanting strawberry crowns in the late summer or early fall. Production starts in the late winter and continues through the summer and into late fall, depending on the area and the varieties grown. Since methyl bromide is not allowed in organic production, crop rotation, green manure crops and compost are critical to control soil-borne diseases and pests.Two types of raised beds are used in plasticulture systems. Narrow beds have two rows of plants with one drip line running between them. The distance between beds averages 40 inches. Drip tape is buried at a depth of about 2.5 inches. Wide beds usually have four rows of plants and two drip lines, with 64 inches between beds. Spacing between plants in both types of bed averages 12 to 14 inches.Plastic mulch is used in both narrow and wide beds and can vary from a single strip of plastic laid between the plants to full bed coverage, where holes must be punched for the plant to develop. Some conventional growers in California use clear plastic, which warms the bed faster, stimulating early-season growth. These growers use fumigation to control most weeds. Black plastic is used in organic production, primarily for weed control. Since the black plastic prevents the sun’s rays from penetrating, the beds remain cool, resulting in slower initial growth of the plants and reduced irrigation frequency compared to clear plastic mulch. There is a plastic mulch on the market that selectively permits soil-warming radiation to penetrate while eliminating the light that promotes weed growth. This type of plastic is preferred by growers in the Southeast.Raised beds provide good drainage. Since they make the flowers and fruit easier to see and reach, raised beds also help growers to forecast yields, while making harvesting easier and faster. Some growers dig deep furrows between the beds so that harvesters do not have to stoop so low to search for fruit. In cold climates, plants in raised beds may be prone to freeze damage. Still, raised beds usually out-produce flat beds. Due to increased aeration and protection from splashing soil particles, plants in plastic-mulched raised beds have less disease.Machinery is available to shape the bed, lay out the irrigation line, and cover the bed with plastic mulch all in a single pass. Sources of bed-shapers and transplanters are listed in the ATTRA publication Season Extension Techniques for Market Gardeners. Or check the following web pages: www.mechanicaltransplanter.com/layer.html, www.marketfarm.com/cfms/mulch_layers.cfm.Recent research indicates that any variety that normally does well in a specific region will do well when grown using plasticulture in that region. However, some of the cultivars that come from the California and Florida systems perform best at a 12- to 14-inch spacing, while many northern cultivars do best at an 8- to 10-inch spacing.By now, growers and researchers in many states have adapted and validated at least parts of the production model described above. Growers should check with their state Extension Fruit Specialist to see if specific plasticulture guidelines are available for their area. Otherwise, a complimentary copy of Nourse Farms’ Success with Plasticulture can be obtained by calling Nourse Farms at 413-665-2658.Plasticulture is not without its serious critics. The plastic has to come from somewhere, and it has to be discarded at the end of the one- to three-year production cycle. Clearly, critics say, this is not an environmentally sustainable system. And, says Cornell University fruit researcher Marvin Pritts, PhD, if you consider all the environmental costs to society, plasticulture is also not economically sustainable in the long run. Pritts also points out that even more plastic?in the form of row covers, tunnels, hoop houses, etc.?is needed to make the system work in cold climates.USDA researchers have shown that fields mulched with plastic cause four times more water runoff than fields mulched with organic materials. Due to this high rate of runoff, fields mulched with plastic suffer up to 15 times more soil erosion than fields mulched with organic matter. Planting grasses or other types of vegetation alongside drainage ditches can reduce the rate of erosion and provide habitat for beneficial insects.Yet, even organic growers?especially those in California, where plasticulture has reigned the longest?are buying into the plasticulture production model. Why? The answer is weeds. Strawberries are notoriously prone to weed encroachment with resultant loss of productivity. Plasticulture provides good to excellent weed control without herbicides. The USDA National Organic Program (NOP) states that plastic or other synthetic mulches are allowed in organic production, provided that they are removed from the field at the end of the growing or harvest season.For more information on growing strawberries, see the ATTRA publication Strawberries: Organic Production at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=13. This publication provides an overview of organic strawberry production methods. It also covers integrated pest management and weed control techniques that can reduce pesticide use in strawberry production. Included are discussions of weeds, pests, diseases, greenhouse production, plasticulture, fertility, economics, and marketing. Lists are provided of further resources, both electronic and in print.