Horticulture Principles and Practices

High tunnels help increase the profitability of family farms in five ways:
1) by extending the production season
2) by increasing the quality and shelf life of the horticultural crop being
produced
3) by minimizing the use of pesticides
4) by ensuring a continuous flow of product when the outside environment is not
favorable for field production
5) by increasing the opportunity to grow more value-added and specialty products.
Vegetables
Extended field production of horticultural crops and in particular vegetables is difficult
because of the extreme fluctuations in temperature and moisture – the two most
significant environmental factors controlling plant growth. Growers producing
vegetables have been using some type of environmental modification in the form of
plastic mulch, drip irrigation, row covers or low tunnels to mitigate the effects of cool
temperatures or fluctuations in moisture. In the United States and other countries
where short growing seasons occur, substantial periods of temperature and moisture
extremes represents a major limitation on crop productivity and an invitation for a host
of insect and disease organisms to infest a stressed crop. This has led growers in these
countries to look at other technologies such as modified environmental structures for
intensive production of horticultural crops. The use of high tunnels for production of
horticultural crops in the United States offers growers several advantages: 1) reduce
temperature and moisture fluctuations during the growing season, 2) lessen disease
and insect pressure and enable the use of biological pest control for both insect and
disease control, 3) extend the Spring and Fall growing seasons 4) enable the production
of crops that have a time to maturity beyond normal field production practices,
5) provide more precise control over water and nutrient application to optimize crop
yield and quality as well as reduce non-point source pollution, 6) reduce/eliminate
wind stress to plants, and 7) deter animals .
Small Fruits
Season extension technologies have been used with small fruit, but most of the utilization
has been for strawberries . Strawberries have been shown to produce extremely high
yields in winter when grown in a vertical system in greenhouses. Winter greenhouse
raspberry production has been investigated in New York. However, the costs associated
with greenhouse small fruit production are higher than those for high tunnel production.
Ideal small fruit crop candidates for production in high tunnels are primocane-bearing
raspberries and thornless blackberries. In many northern states, early fall frost dates
results in only a small portion of the crop of most primocane-bearing raspberry cultivars
being harvested. High tunnel production would extend the period during which
raspberries could be harvested for a much longer period of time, increasing profitability
greatly for the grower. Under field conditions, thornless blackberries often suffer damage
to the flower blossoms during periods of low winter temperatures. Low-temperature
mitigation would improve the percentage of the crop that would be harvested, or in some
cases, make production possible. A preliminary trial of primocane-bearing raspberries
and blackberries in a containerized system, while only recently established, has shown
improved plant growth over that of in-ground plants (unpublished data). Through the use
of greenhouses and/or high tunnels for primocane- and floricane-bearing raspberries
and blackberries, it would be possible to have year-round bramble production in the
Mid-Atlantic States. Constant supply is helpful in increasing willingness of buyers to
purchase produce from a particular source.
20.3 Regionalized Production of Vegetables 623