Colored Plastic Mulch
To reap the greatest benefit from the mulch, the gardener should place it directly on the soil in all the area that is to be covered. Commercial growers use large expensive machines to lay sheets of plastic; while home gardeners must use care to lay the sheets properly. To make sure the soil is covered, smooth out the soil as much as possible and then apply the plastic as tightly as possible. To seal the edges, bury them slightly into the soil. At this point, you may want to cover the sheets with ground up media.
Plain black plastic is the favorite choice for mulching in cool temperatures. It absorbs most of the energy of sunlight al all the significant wavelengths-ultra-violet and infrared. Then it re-emits the energy as long-wavelength (thermal) radiation. Because both sides of the plastic radiates, a lot of the heat is lost in the air. But if the mulch is in good contact with the soil, more heat will be carried into the soil. The main use for black mulch is to retard the growth of weeds. Do not use black plastic that has been painted different colors. It won't work.
In hot climates white plastic is preferred. White reflects heat rather than absorbs it, and keeps the soil cooler.
Clear plastic is a good alternative to black, because it provides greater heating than black. Clear plastic absorbs very little energy, but it passes more into the soil. The underside of the plastic mulch is normally covered with condensed water, and the combination of mulch and moisture lets heat go down from the sun into the soil much like a greenhouse. And the weeds love it! That is the main problem with clear plastic-you will have more weeds.
Color Effects
Choosing plastic mulch the right color may increase your plants' productivity. Plants grow by converting sunlight to chemical energy by photosynthesis, a process of using light to create chlorophyll. Plants can't use all light waves equally, and the colored mulch reflects particular wavelengths of sunlight back up to the leaves of the plants. Different colors reflect different wavelengths, and certain vegetables thrive on different wavelengths.
- Cucumber-dark blue mulch 30% increase over a 3-year period
- Eggplant-red mulch 12% increase over a 2-year period
- Muskmelon-green or dark blue mulch 35% increase over a 3-year period
- Onion-several different colors (red, metalized silver, black) 24%
- Pepper-silver mulch 20% increase over a 3-year period
- Potato-several colors (red, metalized silver, black) 24% increase. Different types of potatoes responded to different colors. Wait until the plants are up before you put down the mulch.
- Summer squash-dark blue mulch 20% increase over a 2-year period.
- Tomato-red mulch 12% increase over a 3-year period.
Yellow mulch seems to attract unwanted insects, and some farmers are using this to their advantage. They lay a row of yellow mulch around the edge of the garden to draw the insects away from their plants. You might want to try this and see if it works.
Mulch Tips
- Use drip irrigation
- Lay mulch as early as you can
- Make sure the soil is moist before you put down the mulch
- Before laying the mulch, soften and smooth the soil
- Stretch the plastic as taut as possible and seal the edges
- When planting, make the holes as small as possible
- Compliment the plastic sheet mulch with row-cover material. There are all kinds of shredded bark and wood available.
- Be sure to select the best quality mulch as possible. Some colors will fade in the sun and will adversely affect your plants.
Most of the research on plastic mulch has been done and is being done at the Pennsylvania State University Plasticulture Center.
