Polytunnel Tomatoes

Trial Criteria for


Selecting Top Greenhouse Performers

Johnny's Research Farm Evaluates the Greenhouse Trials
Collecting trial data at the Research Farm

Greenhouses and poly tunnels of every scale, design, technological level are cropping up everywhere, as growers around the globe discover the many advantages of protected culture. Of the many benefits of greenhouse culture , those topping the list include year-round production, better yield and quality, and protection from adverse weather and pathogens such as early and late blight.

Growing within a protected environment does carry its own set of challenges, however, including increased risk of diseases specific to the greenhouse conditions, such as leaf mold. Crops need to do particularly well to deserve placement in the valuable real estate of a greenhouse or hoophouse.

The research team at Johnny's Selected Seeds is committed to breeding, trialing, and selecting crops well-suited to the greenhouse environment. In the process we've learned a lot about how to identify the top performers, and what distinguishes them from those best grown in the field. Here are some findings from Johnny's greenhouse breeding and trialing team, so you know what to look for, along with some recommendations for varieties we think will perform well in your greenhouses.…

Johnny's research team conducts variety trials at our research farm in Albion, Maine, and in cooperation with growers and university researchers across the globe.

Greenhouse Cucumber Trial
Greenhouse cucumber trial at Johnny's
Johnny's Selected Seeds is committed to breeding, trialing, and selecting crop varieties that are particularly well-suited to the greenhouse environment.
View All Our Greenhouse Performers

This year, for example, Johnny's staff trialed 86 varieties of tomatoes in high tunnels at our research farm, plus 16 different tomato rootstocks! We trialed 24 different varieties of greenhouse pepper, and 18 varieties of greenhouse eggplant. Trialing involves evaluation of a specific set of criteria, including appearance, size, shape, flavor, harvesting for yield data, and plant health, as well as any additional observations of note.

In addition, we collaborate with commercial growers who have a market for the crops, and work with them to trial new varieties. That way, we gather feedback on both production and marketing from multiple locations internationally.

Just what are we looking for when we trial varieties in protected culture? Above all, we want varieties that taste good. Beyond that, we identify a variety as a good choice for protected culture for one or more of the other features listed below.

  • Flavor — always tops our list
  • Vigor — to keep growing longer than the season required for field production
  • Disease resistance — to stay healthy in the reduced airflow and higher humidity of a greenhouse or high tunnel
  • Higher yield — to justify the investment in a structure
  • Ability to do well under low-light conditions — such as red lettuce that retains its color or sunflowers that are daylight-neutral
  • Ability to set fruit without pollination
Greenhouse Symbol
The little greenhouse that signifies a lot
Our greenhouse symbol is reserved for varieties demonstrating outstanding performance in protected agriculture.

Once a variety has proven itself in Johnny's trials, it is designated by a greenhouse symbol. Look for this little symbol next to the variety name in our catalogs and on our website.

Our protected-culture offerings include vegetable, herb, flower, and fruit varieties specifically bred, trialed, and selected to make the most of your valuable undercover, greenhouse, or hoophouse real estate. In this next section, our research team shares some trial findings, recommendations, and favorites for greenhouse culture.

Tomatoes are among the most popular crops for high tunnel and greenhouse production for many reasons: They will produce earlier and later in the season than field crops. Quality is generally much better than field-grown because they are protected from weather-related damage (such as splitting, or diluted flavor from heavy rain), which results in higher marketable yields. Additionally, protected culture provides some protection from diseases caused by wet foliage, such as early and late blight.

That said, the high-temperature, high-humidity greenhouse environment is conducive to a different set of diseases, including leaf mold, powdery mildew, fusarium crown and root rot, corky root rot, and botrytis.

In evaluating dozens of tomato varieties each year for greenhouse culture, Johnny's looks first for three principal sets of qualities:

  • Exceptional vigor and higher yield over a longer season at hotter temperatures than those of the field
  • Resistance to the diseases mentioned above, which are less commonly seen in field production
  • The best flavor and texture possible

Recommended Favorites

Heated Greenhouse Production. The tomato variety that earns our highest rating for heated greenhouse production is Rebelski , as it's known in Europe — also known as DRW 7749 . Rebelski has bright-red, shiny, slightly ribbed fruits averaging 7–8 ounces, that are firm without being hard. It has excellent resistance to powdery mildew and leaf mold, which keeps the crop healthy over a long season. And, it has good flavor!

For those who favor classic heirloom appearance and flavor, Johnny's recent greenhouse tomato introductions include Margold and Marnero , a pair from our French Heritage Collection , that look and taste very much like their heirloom counterparts — but with good texture, improved resistance to disease pressure, and higher yield. Margold preserves the look and flavor of the red-streaked yellow heirlooms, while improving resistance and yield. Its very soft flesh has excellent, sweet flavor and great texture, with an appearance similar to Striped German. Marnero keeps the best attributes of the black tomatoes, while again, improving upon disease resistance and yield. A dead ringer for Cherokee Purple, its flesh is also very soft, with superlative flavor and texture.

The benefit to growers that Margold and Marnero confer is in fruit with eating quality as high as the heirlooms but higher-yielding, due to better vigor and disease resistances than heirlooms, allowing the plants to live longer and stay healthier. By way of example, many greenhouse growers report heirloom yields of one-third to one-half of what they get off red greenhouse beefsteaks, which can be a money-losing proposition. With these tomatoes, we hope to help growers make money off their best-tasting tomatoes.

Kakao is another recent addition to our line of greenhouse tomatoes, with a unique appearance and a flavor all its own. Kakao has the black tomato look in a smaller package, with uniform, round fruits between 4.5–5.5 ounces. Its distinctive dark looks, soft flesh and savory, not-sweet flavor — almost as though it had been sea-salted — make it well-suited to standout branding by variety.

Grafted Organic Tomato Plants. For those looking to get a head start, we also offer growers an outstanding line of certified-organic tomato seedlings . These feature some of our favorite varieties grafted to Estamino rootstock, so as to be more productive and disease-resistant. For greenhouse growers with limited time or opportunity for grafting, our professionally-grafted tomato plants can provide a very cost-effective solution.

Evaluating the Pepper Trial
Evaluating our pepper trial

Bell peppers are another one of the most widely grown greenhouse crops. Since field production of capsicums can be a challenge, and returns on premium-quality bells can be good, they are a natural fit in many growers' greenhouses.

We have recently added a group of bell peppers bred specifically for protected culture. The traits we look for in a good greenhouse pepper include:

  • Good fruit setting under high and low temperatures — some pepper varieties drop blossoms in temperature extremes
  • Big, blocky peppers with good flavor and attractive ripe coloration
  • High level of vigor to keep the plant growing and yields high over a long season

Recommended Favorites

We recommend choosing your protected culture pepper varieties on the basis of your climate and the type of structure — higher- or lower-tech — in which you plan to grow them.

Low-tech/Vegetative. In greenhouses with limited control over temperature and humidity, we recommend growing more vegetative bell varieties like Sprinter (red), Sympathy (orange), and Bentley (yellow). Varieties that are more vegetative put more energy into the plant, a feature which helps them overgrow adversity.

High-tech/Generative. In high-tech greenhouses with excellent control over temperature and humidity — and in lower-tech structures in areas of the country with mild temperatures — you can try growing the more generative varieties of greenhouse bell peppers: Felicitas (red), Orangela (orange), and Moonset (yellow). As mild, even temperatures generally favor vegetative growth anyway, it makes sense to choose pepper varieties that will tend to channel more of their energy toward fruit production, to ensure optimal yield under even, climate-controlled conditions.

Peppers are not able to overcome temperatures that fall below the ideal as well as a more vigorous crop like tomatoes can. That is why we recommend temperature control for best results with all these varieties. In other words, some greenhouse heating may be required to prevent cold stress.

For more details, see our tech sheet Greenhouse Bell Pepper Production .

Cucumbers are another top crop for protected culture, providing a respectable return on the investment required. The desirable attributes we seek in high tunnel and greenhouse cucumbers include:

  • Exceptional vigor to grow over a long season
  • Good resistance to common diseases of protected environments
  • Overall high yields to justify the use of the structure

Recommended Favorites

Our favorite greenhouse cucumber is Corinto , probably the most vigorous cuke we have ever seen. (It may outgrow everything else in the greenhouse.) It offers good disease resistance and high yield potential. Combine those features with its flavor and familiar slicer appearance, and you have in Corinto a winner for protected culture.

Corinto is so productive you will need to prune fruit to one per node, to prevent the plants from being overloaded. To learn how, watch our tutorial Cucumber Pruning Video . For even more details, refer to our tech sheet on Greenhouse Cucumber Pruning & Trellising (PDF), and watch our tutorial video on Lowering & Leaning Your Greenhouse Cucumbers .

Another fruiting crop popular for greenhouse production is eggplant. Growing eggplant indoors in a trellis system can provide steady, high yields of clean, quality fruit. Most greenhouse eggplant is harvested at a baby half-pound size or mini quarter-pound size, but it can be left on the vine to get larger as well.

The traits we look for in greenhouse eggplant variety include:

Evaluating the Eggplant Trial
Evaluating the eggplant trial
  • Fast, vigorous growth for high yield
  • Fruit with good flavor, appearance, and quality
  • Resilience to wide fluctuations in temperature

Recommended Favorites

Jaylo is a shiny black, elongated oval eggplant that firms up early in fruit development, which means it can be picked at a very small size. Jaylo keeps its regal purple color even under hot conditions. It delivers good flavor from spineless, sturdy, high-yielding plants.

Angela is a striking purple-striped, elongated oval eggplant with a white background. The fruit looks great on its own or sold in combination with a black and a white type. With reduced spines on the plant, this is another high-yielding variety with excellent flavor.

For more information, see our tech sheet for Greenhouse Eggplant Production.

Lettuce is a crop that prefers cooler temperatures and lower light intensities, which makes it highly suited for winter greenhouse growing. In addition, lettuce has fairly adaptible cultural requirements and a favorable profit potential. The very cool temperatures and low-light conditions common to the lower-tech winter greenhouses and high tunnels can, however, lead to disease, especially downy mildew, as well as loss of color in red lettuce varieties.

Recommended Favorites

Johnny's exclusive Five Star Greenhouse Lettuce Mix addresses both the above-noted issues. Recently reformulated for more uniform growth rates, the varieties in the mix were selected for their ability to resist downy mildew and hold their color. It's the best mix for baby lettuce and salad mix during the short days of winter.

Hydroponic Lettuce. We now offer a well-rounded selection of lettuce varieties that have undergone rigorous trialing for performance in hydroponic systems. To learn more about our findings, read our article on Hydroponics Trialing at Johnny's , and be sure to review our hydroponic lettuce varieties .

Greenhouse conditions lend themselves well to herbs, though supplemental lighting may be necessary during the darkest months of the year for optimal production, and soil conditions and air flow also need to be monitored. High-quality, local culinary herbs are always in demand, and restaurants can be big consumers. As year-round CSAs and farmer's markets increase in number, the market for premium container herbs has grown apace. While more limited in most areas, the niche market for medicinal herbs can be reliable and profitable as well. The ROI for organically grown herbs can be particularly favorable.

Recommended Favorites

Basil. Johnny's offers a nice line-up of basil varieties that offer resistances to disease pressures common in greenhouse conditions. Eleonora , one of our newer greenhouse additions, has been greenhouse-trialed and has demonstrated intermediate downy mildew resistance.

Organic Herb Plugs. Our certified-organic vegetative herb plugs are very well-suited to container production. With an approximately two-month turnaround time, depending on time of year and climate-controllability of a grower's system, 4"-diameter pots are a popular size in the markets.
Snapdragon Trial
Evaluating the Snapdragon Trial

Flowers, too, are a high-dollar crop, especially when they can be made available for floral events such as Easter, May Day, Mother's Day, graduations, and June weddings. In most locations, field-grown flowers are just not ready that early, so high-tunnel and greenhouse production is essential.

Although nearly any flower can be grown in protected culture, the best choices are varieties that yield a large number of stems per square foot of the valuable space. In systems not tightly climate-controlled, they should be able to tolerate both the cool temperatures of early spring and the hot temperatures of the late spring and summer. Finally, they should be day-neutral varieties, which bloom regardless of day/night length.

Recommended Favorites

Some of our recommended flowers for protected culture include the daylength-neutral Sunflower varieties Sunbright , the Sunrich Series , Sonja , and Soraya . Snapdragon varieties Animation Mix and Costa Mix ; Delphinium ; Lisianthus , and the single-stem Bombay Celosia Series also perform splendidly in greenhouses and high tunnels.

At Johnny's we breed, trial, and select for the best genetics possible , to offer greenhouse growers the most consistently reliable varieties to grow under conditions specific to greenhouse culture.

You can be confident that we assign our Greenhouse Performer symbol to only those varieties that have been carefully trialed and identified as deserving a place within the limited real estate of your greenhouse environment.