Achieving a high yielding bell pepper crop in high tunnels requires a mixture of different management strategies, many of which vary greatly from open-field production.
Becky Sideman, Extension Professor and Specialist at the University of New Hampshire Agricultural Experiment Station, conducted a trial on high tunnel bell peppers in 2015, and shares advice on what to look for in your pepper varieties, as well as additional management techniques that will help you produce strong, healthy yields.
For the trial, Sideman set out to compare the performance of greenhouse and field pepper varieties in unheated tunnels. The peppers were planted inside a 30- by-60-foot high tunnel at the New Hampshire Agricultural Experiment Station and were transplanted in the ground in the high tunnel on May 28.
Sideman used a mix of high-tech greenhouse peppers, low-tech greenhouse peppers, and field peppers for the experiment from both Johnny’s Selected Seeds and Harris Seeds.
As Sideman explains it, the difference between the high-tech greenhouse varieties and the low-tech greenhouse varieties is that the high-tech ones are bred for more environmental controls, and low-tech varieties were bred for less environmental controls.
Overall, Sideman notes that there was a slight improvement in performance with the greenhouse varieties, but not significant.
“They all did well, and the yields were decent. The plants produced anywhere from 3.5 to 5 pounds of marketable fruit per plant over the season. That’s good for bell peppers, and really good compared to field production,” she says.
In the trial, Sideman used drip irrigation and applied all of her fertility pre-plant using organic sources.
“We pre-plant applied most of our nitrogen (N) and potassium and then side-dressed with a small amount of N at the first fruit harvest,” she explains.
Benefits And Challenges Of High Tunnel Production
Producing in a protected environment comes with its high and low points, according to Sideman. The biggest advantage, she explains, is having the protected structure that minimizes environmental stressors and fungal pressure, providing an overall higher-quality fruit.
“Another advantage is an extended growing season,” she says.
“We did our final harvest of those fruit this year in early November, and last year it was Oct. 21. Field production here would typically wrap up in early October as we would expect a killing frost. We were also able to get into the ground three weeks earlier.”
As far as drawbacks, Sideman mentions the appearance of blossom end rot which she believes was a result of improper water management in the tunnels.
“In a tunnel, you need to be on top of your water management and that is something that growers in a field setting are not used to dealing with in many cases,” she says.
To improve water management, Sideman suggests using tensiometers to more accurately measure how much water is available to the plant and how much is being taken up. Making sure that there is enough soil in the root zone is key, she stresses.
What To Look For In Your Varieties
According to Sideman, your market will largely determine what traits you should be looking for in your bell pepper varieties.
“Our work focused on colored bells, but many growers have good markets for other types such as sweet Italians, tapered peppers, etc., which may be something to consider,” she says.
The varieties Sideman worked with ranged in fruit size, some of which were 10 to 12 ounces, and other of which were much smaller.
“One of the varieties has these little, tapered 4-ounce fruit. It was lovely, but your market would have to accept that. Obviously I would look at yield and performance, but at the same time the market characteristics are very important.”
She also stresses the importance of early production that is also consistent, and potential resistance to diseases such as blossom end rot.
Using Beneficial Insects
Pests in the tunnel were controlled using beneficial insects including lacewings and parasitic wasps.
Because the university had been conducting research on habitat plantings to attract beneficial insects, Sideman says she used that as an opportunity to include plantings in the high tunnels. The insects were brought in primarily to control aphids, which she says were a problem throughout most of the season.
“We did do two releases of lacewings which are generalist predators, and they did a great job of cleaning up the aphids. The larvae were feeding right as we released them,” she says.
They also brought in hoverflies, which parasitize the aphids.
“It’s a slower control method, and overall we found that the lacewings were doing most of the eating.”
In order to keep production steady throughout the season, Sideman highlights the importance of adequate pruning.
“We used a system that is sometimes called the Almeria system and it involves conserving four growing points or leaders. We basically trimmed the first fruit set off, kept the first two branches, kept the first two branches from the next split, maintained those four leaders, and then we removed peppers as we went up,” she explains of the process.
She admits that it is typically harder than pruning tomatoes, and that in order to get the most consistent production throughout the season growers will have to learn the fruiting patterns and when they can expect the highest yield based on how their plants are pruned.
Sideman also notes plant spacing as another factor that can influence production and yield. Plants are typically spaced more tightly in the tunnels than they are in the field to more efficiently use space.
“In our trials we spaced the plants in single rows 12 inches apart. I did not try to optimize the spacing, and perhaps growers may be able to optimize it better than we did,” she says.
In general, spacing plants tighter may increase the yield per unit area, however it would decrease the yield per plant, Sideman explains. She suggests playing with the spacing to see what works best for you depending on your structure.