Black plastic can help your garden grow

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Last Updated: 
February 19, 2003

EUGENE - Plastic may have negative connotations for some, but its value in the garden is worth considering. It can mean the difference between red or green tomatoes, sweet or moldy strawberries, and ripe melons or no melons at all.

Ross Penhallegon, horticulturist with the Oregon State University Extension Service, recommends using opaque plastic sheeting to warm the soil for heat-loving tomatoes, peppers, melons and strawberries. The plastic absorbs heat during the day and keeps the soil warm during the night. This is especially helpful during cool spring weather.

And the plastic serves extra duty as it smothers weeds between the rows and reduces evaporation from the soil beneath.

Black polyethylene film in rolls three or four feet wide and 1 to 1.5 mils thick works fine, but Penhallegon recommends using thicker plastic if you want to use it for more than one season. Thin plastic will start to tear apart at the end of summer and can be somewhat messy. If you want something that will decompose by the end of the year, look for black paper mulch.

Before planting peppers, tomatoes, melons or strawberries, lay the plastic on the ground where the plants will grow. Cut 6-inch holes in the plastic every two feet. Dig a hole for each transplant where there is a hole in the plastic, amend the soil with organic matter and plant. Be sure there is enough plastic on all sides to fully cover a mature root system.

If you use drip irrigation in your garden, put the drip lines under the plastic. If you use sprinklers, dampen the soil before you lay the plastic down and cut the holes larger to ensure that enough moisture enters the ground from the sprinklers.

If you don't have a drip hose underneath the plastic, take a pitchfork and punch some holes in the plastic so sprinkler water will drain through. After everything is planted, weigh down the edges of the plastic with rocks or few mounds of soil.

Throughout the summer, the plastic will help control weeds, reduce moisture loss, and help to ripen warm-weather fruits and vegetables. By leaving the plastic in place over the winter, the soil will be weed-free and easy to work come planting time in the next spring. Penhallegon cautions, however, that the plastic gives slugs and snails a place to hide.

Author: Peg Herring