In this second of two articles looking at less popular but lucrative greenhouse/hoophouse crops, we will look at the particularities of growing peppers in protected culture. As I mentioned in last month’s article about growing greenhouse eggplant, if you have grown greenhouse tomatoes, many of the techniques you already know can be applied to this solanaceous crop. There are just a few differing techniques that can help you get the most out of your greenhouse pepper crop.

Ripe, colored greenhouse bell peppers are not as productive a crop as greenhouse tomatoes, so you will have to get a higher price per pound for peppers to make a profit. On the other hand, peppers are a much slower growing crop so you will not have to invest quite as much labor to the same area of peppers as you would in tomatoes.

The difference between growing peppers in the field and in protected culture is much like the difference between determinate and indeterminate tomatoes. In the shorter field season, pepper plants are pruned minimally or not at all and allowed to develop as many fruits and side shoots as possible to form a bush plant habit, much like a determinate tomato. In protected culture, plants are encouraged to grow up and set a controlled amount of fruit, more like a pruned indeterminate tomato. The tall plants take advantage of all the vertical space in the greenhouse, and the fruit pruning keeps the plant productive over a very long season by always keeping the fruit load balanced with the amount of plant that is available to support it.

Starting seeds
The most important thing that needs to be understood if you are used to growing tomatoes or eggplant is that peppers are a much less vigorous, slower growing crop than the other solanaceous crops. This must be taken into account from the very beginning. Whereas some growers take as little as six weeks to go from seeding to setting transplants in the greenhouse for tomatoes and eggplant, two months is typical for developing a transplant-ready pepper plant. They even germinate somewhat slowly, with emergence generally taking place 3-4 days after seeding. 


Peppers growing in a high-tech greenhouse in Canada last June were on track to hit 17 feet by the end of the season. Photo by Andrew Mefferd.


To get good germination, seeds must be held at 80-90°F (27-32° C) constantly from the time of planting until germination. Peppers can be somewhat finicky germinators, and most of the problems I have seen with germination come from not getting the temperature up high enough in the first place and then keeping it up. Using bottom heat from a thermostat-controlled heat mat or a germination chamber are the best ways to get constant heat at precisely the right temperature. Just putting seeds out in a warm greenhouse is not enough to ensure good germination. Dropping nighttime temperatures ensure seeds spend a lot of time at sub-optimal temperatures. 

Even if you are using heat mats or a chamber, it is important to have a thermometer with the probe monitoring the temperature at the depth where the seed is in the soil.  Merely setting the thermostat to the desired temperature is not enough. Thermostats that have gone out of calibration, air leaks, and unexpected heat buildup are all common factors that may cause the temperature to go too low or too high.

The weaker nature of the pepper plant must also be taken into account when deciding on which varieties to use in your growing situation. The breeding work in greenhouse peppers focuses on producing a plant habit that is conducive to growing up rather than branching out. In practical terms this means a pepper plant that has more distance between internodes (taller) and a very even growth habit, producing two evenly matched branches at every node. The contrasting habit observed in field varieties is less distance between nodes (shorter), and a less regular branching habit, sometimes producing more than two branches per node with varying levels of vigor. It is desirable to have two evenly matched branches formed at every node. That way if one branch is damaged, you always have a backup you can use if they are all evenly matched. The other main adaptation of greenhouse peppers is resistance to checking under greenhouse conditions. Field varieties grown in greenhouses may develop checking (cracking) on the surface, similar to what is sometimes seen in jalapeno peppers.

Greenhouse peppers are broken into two major groups, with varieties suited to high-tech or low-tech greenhouse growing. Each group has characteristics that will help it thrive in the particular conditions of the environment that it was bred for. 
Yields and quality are maximized in high-tech greenhouses by growing the plants very fast using high temperature, optimizing fertility and eliminating as much stress as possible. The speed of growth corresponds to the temperature in the greenhouse — the hotter the faster. High-tech greenhouses use a lot of environmental control technology to essentially create pepper heaven. 
However, high heat and fertility and low stress tend to have a vegetative effect on plants, causing them to focus on leaf and stem growth at the expense of fruiting growth (for more on this, see the article I wrote about vegetative/generative steering of greenhouse crops in the June 2013 GFM). Since it is expected that they will be grown in a vegetative environment, peppers bred for high-tech greenhouses are selected to be generative, and focus more on fruiting growth, than those bred for low-tech greenhouses. The idea is that you put a naturally generative variety into the vegetative high-tech greenhouse environment and end up with a balanced plant. 

The greenhouse environments that we refer to as low-tech could encompass anything from a simple greenhouse like a high tunnel with a heater installed, and even to high tunnels in warm areas, like parts of the west coast and southwest United States. What we are not talking about is high tunnels in cold areas of the country. If you live in a shorter season area (most of the northern half of the U.S.), your season likely isn’t long enough and temperatures not high enough to take full advantage of the benefits of the greenhouse pepper varieties, even in a high tunnel. In cold areas without heat, you are probably better off growing field varieties with field techniques, even in a high tunnel.

The characteristics that low-tech greenhouse environments have in common are less sophisticated climate control technology, meaning that temperatures are more likely to get too high during the day and lower than ideal at night. Fertility may also be less optimized and other stresses may be more present than in fancier greenhouses because there is less control over the environment. Temperature, fertility, and other growing conditions that are less than optimal all add up to one thing: plant stress.  And one of the major effects of stress on a plant is to reduce the vigor of the plant.

Varieties intended for low-tech greenhouses are higher in vigor than varieties bred for high-tech greenhouses. Peppers tend to be slow-growing, generative plants by nature.  Generative varieties grown under more stressful conditions (like a low-tech greenhouse) run the risk of losing too much vigor and stalling out. Vigorous varieties bred for low-tech greenhouses will hopefully remain balanced grown in the more generative environment.

The way a variety is bred and slotted is the best way to choose a variety that will thrive under your conditions.  Low-tech varieties run the risk of getting too vegetative in a high-tech, bells-and-whistles kind of greenhouse environment. And high-tech varieties may get too weak when their vigor is sapped by more stressful conditions tin a low-tech greenhouse environment. That said, the slotting is not so rigid that varieties don’t sometimes perform well outside their intended environment. It is worth trialing small numbers of a few different varieties in your greenhouse to see what really performs the best for you.
A Johnny’s, we looked at 24 varieties bred for greenhouse production and chose to offer these: For high-tech greenhouses: Felicitas,  Orangela, and Bentley. For low-tech: Sprinter,Sympathy, and Moonset.

Propagation and transplanting
Greenhouse peppers are propagated in much the same way as greenhouse eggplant. Refer to the article in last month’s GFM for seeding and medium recommendations.  Once you have a seedling, grow at a daytime temperature of 70-74°F (21-23° C) and nighttime temperature of 68°F (20° C).  Since peppers spend a relatively long time as seedlings before they are transplanted, it is important that they receive supplemental fertility and not just water. Fertilize with a complete nutrient solution, with an EC of 1.5-2 and a pH of 5.2 or the equivalent to keep the plants green and healthy. When first transplanting into the greenhouse, maintain a flatter than usual temperature profile of 73°F (23° C) during the day and 70°F (21° C) at night. Use this temperature regime for the first week to promote rapid vegetative growth and rooting in.

As with any greenhouse crop, if you are growing in soil, make sure to get the saturated media extract soil test instead of a standard field soil test. This test takes into account the greater amount of fertility necessary over the long greenhouse season, and will show your fertility needs much better. If you are growing hydroponically, consult your fertilizer supplier about a program suitable for optimizing greenhouse pepper growth.

Greenhouse pepper plants may be grown with two or four heads per plant. Two heads will result in larger peppers, and plants may be able to bounce back from stressful conditions more quickly since there is less demand on each root system. Two heads is most common here in North America because the American market is for large bell peppers. Four heads is common in Holland, where large peppers are not as important.  In areas with very hot summertime temperatures, use two heads per plant for resilience. 

When it comes time to transplant, lay out the rows so that you can accommodate 6-7 stems per square meter (a square meter equals nine square feet). The most common way to achieve this packed planting density is to use a double row of plants, with approximately a foot between plants and six inches between stems. Use the same stem spacing for two or four-headed plants, simply using half as many plants with four-headed plants. You can increase the spacing between stems if you want to reduce planting density. 

Stems are anchored to two overhead wires two feet apart, with a walkway three feet wide. This two foot wide double row with a three foot wide walkway is a common way to set up greenhouses, since this wire spacing can accommodate the common spacings of all the commonly grown greenhouse vining crops- tomatoes, cukes, eggplant and peppers.  With this greenhouse setup you can change crops without having to change your trellising. For more on this greenhouse spacing, see my article on hoophouse improvements from the April 2013 GFM. 

After the first week in the greenhouse, lower the nighttime temperature to 65-68°F (18-20° C), and maintain daytime temperatures as close to 73-75°F (23-24° C) as possible. Peppers have difficulty setting fruit at nighttime temperatures above 68°F (20° C), so it is important that temperatures at least come down that low at night.  Cooler nighttime temperatures will result in a more generative plant, warmer nights will encourage vegetative growth. Though it will be impossible to maintain daytime temperatures that low in most areas during the summer, the takeaway is that pepper plants don’t actually need it that hot to thrive. This is also important to keep in mind in hot areas, that if pepper growth suffers during the summertime it may be due to the plants getting too hot.  Some growers try to help their peppers through the excessively hot parts of the summer by whitewashing or applying shade cloth to the greenhouse.

In the next issue of Growing for Market, Andrew will explain how to trellis and prune greenhouse peppers for maximum production.

Andrew Mefferd is the owner with his wife, Ann, of One Drop Farm in Cornville, Maine. He is also a trial technician for greenhouse crops at Johnny’s Selected Seeds Research Farm. He can be reached by email.