As we initiate our third year of hoop house vegetable trials, now is an appropriate time to share some observations from the previous two years. For those of you unfamiliar with this topic, the hoop house is one of several technologies growers have adapted in an effort to master mother nature.
Hoop houses, (referred to as over-wintering structures by the nursery trade), are generally quonset-shaped structures constructed of metal or plastic hoops (bows). They are covered with one layer of 6-mil greenhouse grade polyethylene film and are ventilated by rolling up the sides. There is no permanent heating system and no electrical connections. The only external connection is the irrigation supply line.
The ends of the houses are framed and covered with polyfilm or a rigid material such as fiberglass. Most end walls are fitted with doors, however a few can be removed entirely permitting greater access. Hoop houses range in width from 14-20 ft. and in length up to 96 ft.. Hoop houses, ranging in price from $1.25- $2.00 per sq. ft., are relatively inexpensive compared to greenhouses.
Traditionally high value crops such as tomatoes are grown in hoop houses to justify the additional expense. Other crops reported being grown include strawberries, raspberries, cut flowers, melons, eggplant, pepper, and summer squash. These crops are typically marketed direct to the public.
Hoop houses should not be regarded as freeze protection devices although they can provide a limited degree of protection. On the morning of 4/12/97 our hoop house tomato crop survived despite a 27°F. ambient (outside) air temperature.
One benefit of the hoop house often overlooked is storm protection. A crop is only worth as much as the protection provided by a 6-mil sheet of plastic. During the fall of 1996, our hoop house tomato crop escaped the ravages of a hailstorm accompanied by 70-mph wind. Seeing is believing.
There is less incidence of foliar disease in hoop houses primarily because crops are sheltered from rainfall. Our 1997 hoop house tomato crop never required a foliar fungicide application. Consequently, we saved on chemical and labor expense.
Crow and mockingbird damage to tomato fruit is an annual occurrence in our plots. To date, vertebrate pest damage to crops grown in our hoop houses hasn't been a problem even when the houses have been fully vented. Evidently, crows are suspicious enough of the covering they don't venture inside. If animals become a problem, covering the side vents with a fabric mesh should remedy the situation. It's a good idea to have some plastic mesh on hand even if you aren't experiencing animal problems. During the spring, it makes an excellent windbreak for young transplants.
The plastic film is the component of the hoop house that is primarily responsible for crop protection. Consequently, we have chosen not to remove film from our houses during the summer as some growers do.
Hoop houses have proven effective in extending the growing season in both spring and fall. The primary benefit is earliness. Based on our research and the experiences of other growers about one month of earliness is normal for tomato and pepper. Earliness is a combination of being able to plant two weeks earlier than field planting and faster maturity inside the house.
Temperature management within the hoop house is the single most difficult task. First time growers often underestimate the capacity of the house to gain heat especially on cloudy days. As a rule of thumb hoop houses should be vented before internal air temperature reaches 90 degrees.
The amount of vent opening will depend on the desired growing temperature, the ambient temperature and wind speed. Don't panic if you miss the mark by a few degrees. We noticed no long-term damage to a tomato crop when the air temperature exceeded 100 degrees for a few hours.
Every crop has its ideal growing temperature. We try to adjust side vents to maintain a growing temperature of between 80 and 85 degrees for bell pepper and tomato, and 90 degrees for cucurbits, eggplant and hot pepper.
During cool weather, roll down the sides in the early evening to entrap as much heat as possible. As the season progresses sides can remain open when night temperatures don't fall below 65 degrees. A mini-max thermometer is excellent for monitoring day and night temperatures. If the forecast calls for a chance of rain during the night go ahead and close up the house before retiring for the evening.
When air temperature exceeds 90 degrees at plant level, we start thinking seriously about applying shade fabric. In Oklahoma, this can be as early as mid May or as late as mid June. We currently use a 55% shade fabric on all our houses. There is no substitute for experience when it comes to hoop house temperature management. A good way to develop management guidelines for your hoop house operation is to keep good records. To do otherwise is to court failure.
The past two years we're employed the use of raised beds in all of our hoop houses. Each bed is filled with two drip irrigation lines and covered with plastic mulch. Transplants grown in 1.5-inch pots are used to encourage earliness. As the crop matures, support structures such as cages are installed. Supplemental nitrogen is applied via the drip system based on a fertilizer schedule. Irrigation scheduling is determined by irrometer readings.
To justify hoop house production, yields must be greater than field-grown crops. In addition, growers must obtain higher returns for their early market produce. The table below summarizes yield results of tomato and pepper crops grown during 1997 in our hoop houses.
To date, hoop house culture in Oklahoma has found limited use. However, because these structures reduce the risk of production by providing greater control over the environment, the potential for expanded use in our geographic area is tremendous.