The use of plastic mulch in vegetable gardens has many advantages and also a few disadvantages.  Gardeners may be confused about whether to use black, clear or colored plastic. Some of the differences in benefits and disadvantages of these are described below. 

 The most widely used plastic mulch is black.  Black plastic prevents weed growth and clear plastic does not, requiring herbicide use or fumigation to control weeds.  Weed growth under colored mulches depends on the degree of opacity of the mulch.

 Black Plastic Row Coverhttp://www.umext.maine.edu

 Advantages of using plastic mulch

  1. Increases soil temperature, allowing earlier planting and earlier harvest, and promotes plant growth in cooler climates.
  2. Soil compaction is reduced which improves root growth.
  3. Fertilizer leaching is reduced because excess water runs off the plastic.
  4. Waterlogging from excessive rain is avoided.
  5. Drying of soil from evaporation is reduced.
  6. Crops are cleaner and less subject to disease caused by soil-borne pathogens because they are not in contact with the soil or rain-splashed soil.
  7. Weed control with black plastic eliminates the damage to roots caused by cultivation to remove weeds.
  8. Weed control (black and colored mulches).
  9. Harvest of crops can be 2-14 days earlier with black plastic and as much as 21 days earlier with clear plastic, depending on the crop and the temperatures.
  10. The “chimney effect”:  CO2, which is required for photosynthesis, builds up under the plastic and can only escape through the planting holes, causing a higher concentration around the growing leaves.

 Disadvantages of plastic mulch

 1.   Cost of mulch and irrigation equipment.

2.    Soil erosion can increase between the mulched rows.

3.    Weeds may grow through the planting holes close to the crop plants.

4.    Must be removed from the garden annually, along with the drip or   soaker hose irrigation tubes.   Biodegradable plastics are becoming available.

High Yield Red Tomato Mulch: A bright red plastic mulch to spread on top of the vegetable garden.http://www.parkseed.com

Colored mulches are gaining in popularity and some research studies have been done to see if they can increase yield, help reduce insect and disease problems, or promote earlier harvests.  The most widely studied color is red.  Some studies have shown increased and/or early harvest in crops including tomato, pepper, melon, and zucchini, while others have shown no significant difference.  One study compared red mulches from five different manufacturers.  The mulches varied in opacity and longevity of color and included one biodegradable product.  Increased yield was obtained in the products that were opaque and did not fade during the growing season.  The biodegradable product faded as it broke down (broken down by sunlight) and did not increase yields.  In one study, it appeared that red mulch may reduce severity of early blight of tomato.  Using red mulch may increase plant growth and yield, and opaque products will have the same additional advantages as black mulch. 

www.extension.umn.edu  Colored mulch trial on raised beds at University of Minnesota.

 Reflective mulches have also been receiving some attention and they may be helpful in reducing aphid problems by confusing them.  Some colored mulches attracted the green peach aphid (pest of vegetable crops and virus vector), especially yellow mulch.  Yellow also attracted striped and spotted cucumber beetles.  Yellow traps are often used to monitor insect populations because it attracts them, so yellow mulch is being considered as an option for trapping insects on the edges of a field, much like trap cropping. 

 Prior to installing plastic mulch in the garden, amendments to the soil such as lime, fertilizer and organic matter should be incorporated into the soil.  A soil test is recommended to determine amounts to be added and can be done at the UConn Soils Laboratory.  Soil should be moist but not saturated.  Install drip irrigation or soaker hose.  Plants could also be watered through the planting holes.

Having raised beds will aid in early warming of the soil and they should be slightly higher in the center to allow water to run off, avoiding puddling on the plastic.  Anchor the plastic with soil and/or rocks, etc.  Smooth the soil well to allow for good contact between the plastic and the soil surface. 

 It’s too late for this year, but there are several advantages to laying the plastic and irrigation system in the fall, including: 

  1. Soil is drier in the fall, making it easier to work with.
  2. If fumigation is necessary, soil moisture and temperature are likely to be better.
  3. Can allow transplanting 10-14 days earlier in the spring.

If you have any questions about using plastic mulch, give us a call at the UConn Home & Garden Education Center at (877)486-6271 (toll free in CT) or (860)486-6271 (outside CT) or email us at ladybug@uconn.edu.  

 JA