Peppers 201

Photos courtesy of Christopher J. Currey

Brightly colored peppers are one of the three most popular fruiting vine crops grown hydroponically in greenhouses, along with tomato and cucumber. The U.S. market produces nearly 400,000 pounds of peppers from hydroponic systems each year.

Greenhouse peppers, like all hydroponic food crops produced in greenhouses, are a value-added product, and this article will focus on some opportunities to maximize the quality of pepper crops.

As with any fruiting vine crop, pepper fruit quality is one of the most important characteristics for any grower’s product. This is especially true for peppers grown hydroponically in controlled environments, as the premium fruit quality of colored, ripened peppers sets them apart from their green, field-grown counterparts.

Compared to cucumber and tomato, pepper is a cooler-growing plant. Although the optimal temperature for flowering and fruit set is ~61° F, subsequent fruit development and total yield is maximal at ~70° F. A day (16-hour) and night (eight-hour) temperature regime of 72 to 73° F and 64 to 65° F, respectively, will result in a target average daily temperature of ~70° F for optimizing yield.

Two mineral nutrients, calcium (Ca) and potassium (K), play important roles in fruit growth and development.

Fruits have a high demand for Ca and K due to the rapid cell division and expansion, osmotic regulation, and other factors. However, one complicating factor is that both nutrients are positively charged ions, or cations- Ca²⁺ and K+. Since both nutrients are taken up passively through bulk flow, they can antagonize one another, with excessive concentrations of one diminishing the uptake of another. In order to avoid antagonisms between K and Ca, the ratio of K:Ca should be around 1.5:1.

Periodically measure the actual concentrations of these two nutrients to determine their ratio in recirculating nutrient solutions to avoid imbalances from developing. There are several characteristics contributing to fruit quality, including the thickness of the pericarp or wall of peppers, as well as fruit acidity. However, the sugar concentration in peppers — grown for their mild fruit taste characterized by sweetness — is a defining characteristic of the fruit and is quantified as brix (°Br), the equivalent of grams of sucrose dissolved in 100 grams of solution.

Thankfully, brix can be a fairly easy measurement to make in-house. By using a hand-held refractometer or brix meter, peppers can be squeezed to expel liquid from the flesh into the brix meter and producers can readily sample the crop to determine how environmental conditions, cultural practices, and stage of ripeness affect sugar concentrations. While there are no standard values that a crop must meet to be marketable, targeting a brix of ~8 is considered good, whereas ~12 is characterized as excellent.

Sweet, blocky bell peppers are the dominant fruit class for hydroponic greenhouse pepper crops, and for good reason — they are popular with consumers. However, either focusing on a different type of pepper or diversifying the variety grown may improve sales. An increasingly popular pepper variety are the lunchbox or snack peppers. These are simply miniature versions of the red, orange and yellow bell peppers that are already grown in greenhouses.

Characterized by a mild, sweet flavor, these are popular for fresh eating and are particularly well-suited for snacks and appetizers.

On the spicier side of peppers, many of the varieties marketed green like Anaheim, jalapeno, and serrano peppers, are mostly field grown. However, if sufficient value can be added to hot peppers, soilless production in controlled environments may warrant producing them. For example, the habanero peppers in Fig. 1 are grown hydroponically in a greenhouse for processing into boutique hot sauce, which adds enough value to the peppers while ensuring a reliable and consistent supply of fruits for processing.

While not a sweet pepper nor a spicy pepper, shishito peppers (Capsicum annuum var. grossum) are quickly cooked by blistering them and are becoming a trendy appetizer. Shishito peppers differ from sweet bell and snack peppers in that they are harvested when they are still green, not ripe and colored. Although they can be grown in fields, the popularity of this crop with retail consumers or wholesale restaurant customers offers year-round opportunities for growers.

Whether sweet or spicy, the fundamentals of producing vine crops like tomato and cucumber are mostly applicable to pepper production. Keep these tips in mind when growing your pepper crops.