Season Extension of Vegetable and Small Fruit Crops in West Virginia
By Lewis W. Jett, WVU Extension Service commercial horticulture specialist
Extending the traditional growing season has many advantages for produce growers and market gardeners in West Virginia. Earlier harvesting often secures a higher market price for produce and overall higher net farm income. Oversupply of produce typically drives prices downward, but off-season production enables growers to enter the market well before the market becomes glutted or after most supply has been sold.
By establishing the planting earlier, there is a potential for reduced insect and disease pressure for many crops. Many pests often become a problem as the season progresses and temperatures get warmer. Establishing a crop in the off-season makes it possible to avoid many pest outbreaks.
Methods of Season Extension
There are several ways to extend the traditional growing season in West Virginia. Using transplants instead of direct seeding will often result in an earlier harvest for most vegetable crops. Most vegetables can be transplanted. Even vegetables that are never traditionally established by transplants (including beets, peas, and sweet corn) can be transplanted if the right type of container is used. Transplant age can have a significant effect on date of first harvest. If grown in a large transplant container (> 4” diameter), tomatoes and peppers can be established as 8- to 10-week-old transplants, which will reduce the time to first harvest (Figure 1).
When using transplants, it is important to start with quality seed. Small, irregular seed, such as carrots, lettuce, and tomatoes, can be purchased as pellet seed, which has a clay coating that makes the seed round and easier to seed by hand in the transplant container. Usually one or two seeds are planted in each container or cell. The most vigorous seedling is kept by thinning when the first true leaves appear on the seeding.
Many transplants can be conditioned for transplanting in the open environment by “hardening” them off, which usually means placing them outside for a couple hours each day about two weeks before transplanting to get some wind and slightly lower temperatures on the plant.
|Figure 1. Healthy transplants result in earlier, uniform harvest.|
Raised Bed Culture
Raised beds, in which the soil is ridged or listed to form an elevated growing area, can significantly improve crop growth. Raised beds are typically 8 to 16 inches in height and may be framed with boards or posts to a width of 36 to 48 inches (Figure 2). The framed, raised bed can be filled with topsoil or other organic material (compost) to create an ideal growing medium for many vegetable and small fruit crops.
Raised beds are an excellent way to create a new soil that may be loose and friable for root crops such as potatoes, carrots, and beets. Soil in raised beds will be warmer than flat soil since more of the soil surface is exposed to sunlight. Because the loose soil increases drainage, the crop will have to be irrigated more frequently. With raised beds, a drip irrigation tube or soaker hose will be needed to water the crops.
|Figure 2. Raised beds accelerate plant growth.|
Irrigation is the most important investment for growing vegetables and fruits in West Virginia. Unpredictable rainfall often creates periods of too much or too little water. Each scenario can be devastating for vegetable and fruit crops, depending on the season. Yield and quality of most vegetable and small fruit crops are determined by even application of water through the growing season.
Drip irrigation is a system in which water is slowly applied to the root zone of the crop through small dripper hoses (Figure 3). With water applied directly to the root zone, the foliage does not become wet. Using drip irrigation results in less water being lost from evaporation, and diseases (many of which require free water on the leaf surface) will be less of a problem. Drip irrigation reduces overall water use compared with most other ways of watering crops. Small drip irrigation kits can be purchased for irrigating areas as small as a garden.
Figure 3. Drip irrigation conserves water and results in even growth of crops.
Fertigation is the technique in which fertilizer is applied through the irrigation system. Many fertilizer sources can be dissolved in water and injected directly into the water lines during irrigation. Fertigation applies nutrients to the plants evenly throughout the growing season and results in a significant reduction in fertilizer usage compared with applying most of the nutrients before planting.
Row covers are an indispensable tool for season extension. Row covers are lightweight, fabric materials that can be placed over the crop (floating) or suspended above the crop on wire hoops or frames. The row covers trap solar heat that builds up during the day and keeps the temperature from becoming too low around the crop.
Row covers come in a variety of types. Lightweight fabric (<0. 5 oz/yd2), which is an insect barrier or screen, can be used to prevent harmful insects from feeding on vegetable and fruit crops. Medium weight (0. 5-1. 0 oz/yard2) fabric will provide about 4°F frost protection with 85% light transmission. Heavy weight row covers (> 1 oz/yd2) will provide winter freeze protection for many crops that are over-wintered in cold frames, low tunnels, and high tunnels in West Virginia. When used within a high tunnel, row covers can be twice as effective as when they are used in the open field. Row covers can be recycled, and after use, they can be simply folded and placed in a storage shed until next year.
Low tunnels are actually “mini-greenhouses.” They are usually 18 to 48 inches in height, 2 to 6 feet in width, and of varying lengths (Figure 4). The hoops or bows can be plastic pipe (PVC), wire (9 ga.), or aluminum conduit (EMT). Row cover or clear plastic can be placed over the hoops to protect the growing crops from rain, wind, and wildlife as well as to increase the temperature of the air and soil surrounding the crop. Low tunnels are very useful when used for relatively low-growing crops such as salad greens and other cool-season crops that can be overwintered. Low tunnels can be used for early season protection of tender crops, such as peppers, melons, squash, tomatoes, and beans.
Low tunnels are relatively inexpensive to construct and, if used properly, can accomplish almost as much season extension as a high tunnel. When used in combination with a high tunnel, low tunnels are extremely effective in extending the season.
|Figure 4. Low tunnels can significantly accelerate harvest of many crops.|
One of the most effective tools for extending the traditional growing season is called a high tunnel or hoop house. A high tunnel is a plastic-covered structure that traps solar energy to increase air and soil temperature, giving the grower the opportunity to plant and harvest earlier or later in the year (Figure 5). Crops are grown directly in the soil under the high tunnel and are irrigated as needed through drip tubing or soaker hoses. The high tunnel protects the plants from intense rain, snow, wind, and hail as well as harmful insects, wildlife, and diseases that can reduce yields over the course of the growing season.
High tunnels can be constructed from a variety of materials such as steel pipes or plastic tubing. The size depends on the amount and type of vegetables or fruits grown. A high tunnel can be used to grow just one vegetable (tomatoes) or a combination of fruits and vegetables as a mixed cropping system. High tunnels can be stationary or moved to different sections of the field or garden to give a crop an early start. Many vegetables and fruits can be intercropped within the high tunnel, and approximately three crops per calendar yield can be harvested. Most crops grown using high tunnels are ready to be harvested four to five weeks earlier (or later) than crops grown in an open field or garden, which can significantly lengthen the farmers market season in West Virginia.
Figure 5. High tunnels are low-cost greenhouse structures that accelerate crop growth.