COLUMN: Lengthening the growing season for warm season crops

Garrett Ford

As the days are becoming noticeably shorter, and evening temperatures are plummeting, farmers are counting the days before the temperatures drop into the 30s, which will cease the growth of warm season garden crops.

It is nice to feel a change in temperature and see a change in leaf colors but for farmers, it means that warm season vegetable growing season is wrapping up. Warm season vegetables include squash, tomatoes, and peppers. The good news is that using different techniques which are becoming increasingly popular, it is possible to squeak by a few more weeks of production.

It is well-known that a heated and ventilated greenhouse makes it possible to grow some warm-season vegetables throughout the winter months. Of course, a considerable investment in a structure, heating and artificial lighting is needed to establish this type of production. For those interested in extending the growing season without going as far as setting up a complete greenhouse, there are some other options. High tunnels have proved to be a good option for our area. Summer and fall crops can be protected in these structures to enable tomato harvest into November, and possibly later, if additional cold protection is provided by using frost blankets and supplemental heat. With “season-extended crops” the use of early maturing and small fruited varieties, or those specifically recommended for high tunnel production, would be a good place to start for determining cultivar choices.

Season extension benefits and techniques go beyond tomatoes and high tunnels. The use of “low tunnels” and frost blanket type materials can also provide some protection for warm season crops from early, but brief, cold weather. For example, frost blankets placed over beds to protect from an early October frost may enable several additional weeks of harvest of summer squash, beans, or peppers. A “low tunnel” is a temporary structure that is placed over crop plants to support an insulating horticultural fabric. In addition to protecting cold sensitive crops, this resource can also be used to enhance the growth of cool season crops for which growth would be hindered by conditions such as cold, windy weather.

Maintaining vigorous crop growth during the cool season can be a challenge due to slower chemical and microbial processes in cool soil. The loss of soil nutrients during cool, wet periods to leaching and denitrification can also reduce the availability of nutrients for vegetable plants during cool weather.

The use of dark colored sheet mulch materials can be helpful for keeping soil temperatures a little more favorable and for keeping soil moisture in a desirable range. The use of soluble nutrient sources is one means of providing readily available nutrition to cool season crops, but these sources are susceptible to leaching. The nutrient availability to plants of organic sources can be reduced due to slow rates of biological processes in cool soils.

Fish emulsion products seem to be good organic sources to which cool season crops show a rapid response following application. No single fertility management approach will fit the needs of all cool seasons and season extension growers, and all should experiment with various options to determine what works best for their situation.

Garrett Ford is the agriculture educator for the Cherokee County OSU Extension office.

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