Package of Johnny's Selected Seeds
Package of Johnny's Selected Seeds
What We Look for in Protected Culture Varieties

Trial Criteria for Greenhouse & Hoophouse Varieties

What Makes a Variety Right for Protected Culture?

In this article...
Our Trial Criteria »
The Protected-Culture Symbol »
Top Crops for Protected Culture »
Greenhouse Tomatoes »
Greenhouse Cucumbers »
Lettuce & Greens for Protected Culture »
Flowers for Protected Culture »
Further Reading  »

High tunnels, low tunnels, and greenhouses are sprouting up on farms and homesteads everywhere, as more growers discover the many advantages of protected culture. The benefits of growing under cover include season extension, better crop quality, and protection from bad weather and certain pathogens, such as early and late blight.

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

Johnny's Selected Seeds is committed to breeding, testing, and selecting crops that are well-suited to protected culture. In this article, we'll tell you a bit about how we identify these varieties, then provide some recommendations for the ones we think will perform well in your high tunnels, low tunnels, or greenhouses.

Above & Beyond Flavor — What We Look For

Tunnel Trials
Tunnel Trials

Johnny's research department conducts variety trials at our research farm in Albion, Maine, in cooperation with growers and university researchers around the country, and in select locations globally.

This year, for example, Johnny's staff trialed 85 varieties of tomatoes in unheated high tunnels at the research farm. 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. To identify the best varieties for heated greenhouse production, we typically find commercial growers who have a market for the crop and work with them to trial new varieties. That way, we gather feedback on both production and marketing from multiple locations around the globe.

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 following reasons:

  • Vigor, to keep growing through a longer season than 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.
  • Cold hardiness, for winter production.
  • Ability to do well under low-light conditions, such as red lettuce that retains its color.

Our Protected Culture Symbol

Johnny's Greenhouse Symbol
Reserved for varieties that do well
when started in, or grown in,
a protected environment.

Once a variety has proven itself in Johnny's trials, it is designated by a red "protected culture" symbol. Look for the 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, we give some specifics about our current recommendations for protected culture.

Top Crops for Protected Culture

Tomatoes for Protected Culture

Rebelski Gets Our Highest Greenhouse Rating
Trellised Greenhouse Tomatoes

Tomatoes are one of the most popular crops for high tunnels and greenhouses. 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.

The high-temperature, high-humidity environment, however, is conducive to a different set of diseases — including leaf mold, powdery mildew, fusarium crown and root rot, corky root rot, and botrytis.

So, when choosing tomato varieties for protected culture, Johnny's looks for these three primary factors:

  • Exceptional vigor and higher yield over a longer season at hotter temperatures than those in 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 gets 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 oz that are firm without being hard. It has excellent disease resistance to powdery mildew and leaf mold, which keeps the crop healthy over a long season. And, of course, it has good flavor!

Unheated Tunnel Performer. A top producer in our unheated high tunnel trials is Arbason, available as Organic seed. Fruits average 7–9 oz in weight, and plants are highly resistant to tobacco mosaic virus (TMV).

Cucumbers for Protected Culture

Trellised Greenhouse Cukes
Trellised Greenhouse Cukes

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 Favorite

Greenhouse Production. 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. For more details, refer to our tech sheet on Greenhouse Cucumber Pruning & Trellising (PDF), or watch our Cucumber Pruning Video.

Lettuce & Greens for Protected Culture

Five Star Greenhouse Lettuce Mix
Five-Star Greenhouse
Lettuce Mix

The cool temperatures and low-light conditions typical within the winter greenhouse or high tunnel can lead to disease, especially downy mildew, and loss of color in red lettuce varieties.

Recommended Favorites

Lettuce. Johnny's exclusive Five Star Greenhouse Lettuce Mix addresses both of 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.

Greens. Other greens that work well in the fall and winter unheated high tunnel include the cold-hardy Claytonia, Minutina, Persian Cress, and Vit Mâche.

Cut Flowers

Hoophouse Flowers
Hoophouse Flowers

Flowers, too, are a high-dollar crop, especially when they can be available for popular floral events such as Easter, May Day, Mother's Day, graduations, and June weddings. In most locations, field-grown flowers are 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. They should be able to tolerate both the cool temperatures of early spring and the hot temperatures of the late spring and summer high tunnel. 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.

Our Protected Culture Commitment

At Johnny's we breed, trial, and select for the best genetics possible, in order to offer greenhouse growers the most reliable varieties to commit to the limited available real estate given to protected cover.

You can be confident that we assign our Protected Culture symbol to only those varieties we've carefully trialed and subsequently identified as best suited for the protected culture environment.

Learn More

Learn more from the following additional resources.

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