Selecting Top Greenhouse Performers
Greenhouses and poly tunnels of every scale, design, and technological level are cropping up everywhere, as growers around the globe discover the advantages of protected culture. Of the many benefits of greenhouse culture, season extension, better yield and quality, and protection from adverse weather and pathogens such as early and late blight top the list.
Growing within a protected environment does carry its own set of challenges, however, including limited space, more intensive plant maintenance, and increased risk of diseases specific to greenhouse conditions, such as leaf mold. Crops need to perform 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 varieties 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.
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In 2015, 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, plant habit, yield, 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. In this 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 if it excels in one or more of the other qualities listed below.
- Flavor — Always tops our list.
- Vigor — To keep growing longer than the season required for field production.
- Plant habit — The space limitations of indoor growing favor more compact plants, requiring less pruning and maintenance.
- Disease resistance — The reduced airflow and higher humidity of a greenhouse or high tunnel promote specific foliar diseases, and insects like whiteflies can transmit viruses quickly from plant to plant.
- 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. In addition, some disease symptoms are heightened when light transmission is restricted by glazing material.
- Ability to set fruit without pollination — A greenhouse enclosure limits access to flowers by pollinators such as bees and butterflies. This is especially critical with cucumbers grown indoors, and is the reason why parthenocarpic varieties are recommended for indoor culture.
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: For one, they will produce earlier and later in the season than field crops. Second, 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. Most importantly, tomatoes are a high-value crop in many markets, and they can produce a steady crop over a long period. A single planting can thus provide a high return on investment with a little regular maintenance.
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. These fungal diseases are able to spread very rapidly in the close quarters of indoor tomatoes. Soilborne pathogens can build up large populations if tomatoes are grown regularly in the same hoophouse ground; often the high value of tomatoes entices producers to grow them more frequently than they should, without rotating to less valuable crops to break disease cycles. Additionally, symptoms of the tobamoviruses (tobacco mosaic virus and tomato mosaic virus, or TMV and ToMV, respectively) are exacerbated by the restricted light transmission found in greenhouses and high tunnels.
In evaluating dozens of tomato varieties each year for greenhouse culture, Johnny's looks first for four principal sets of qualities:
- 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.
- More compact, "polite" plant habits, which reduce the need for pruning and allow better airflow amongst the plants.
- The best flavor and texture possible.
HEATED Greenhouse Production
Go-To Varieties. We carry two "go-to" varieties of big, round, red tomatoes that are highly productive, feature balanced plant habits, and still deliver good tomato flavor. Geronimo is a long-time standard, producing reliably hefty yields of 8–10 ounce, classic red slicers. Bigdena is a more recent introduction, featuring slightly larger fruits than Geronimo, with a taller fruit profile that affords the chef an extra slice or two. Both feature comprehensive disease packages and perform well in both the heated greenhouse and high tunnel. For a more compact plant habit, choose Frederik; it requires the least pruning and training, though most growers find the flavor a bit less sweet than the aforementioned Geronimo and Bigdena.
Best All-Round Performer. 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!
Hy-looms. For those who favor classic heirloom appearance and flavor, Johnny's recent greenhouse tomato introductions include Margold, Marnero, and Marbonne, which make up our French Heritage Collection. They look and taste very much like their heirloom counterparts — with improved resistance to disease pressure and higher yield potential. Margold preserves the look and flavor of the red-streaked yellow heirlooms, while adding leaf mold resistance, improving fruit uniformity, and improving marketable yield. Its very soft flesh has sweet and mild tomato flavor and thick, juicy texture, with an appearance similar to Striped German. It's a great BLT or burger-topping tomato. 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 the complex flavor and meaty texture you would expect from your favorite "black tomato" heirlooms. Marnero stands out in Caprese salad, fresh pico de gallo, or any other preparation where raw tomato is the focus of the dish. Marbonne represents the classic French 'Marmande' heirloom type, with rich scarlet skin and a crown accented by deep ribs. Because this type is so popular throughout Europe, there are actually several hybrids on the global market that resemble the original Marmande, but we have found Marbonne to be the best of the lot. It is very early maturing (as are most Marmande-types), and is the highest yielding of the French Heritage tomatoes. It is also arguably the sweetest and most universally appealing in flavor. There is no wrong way to prepare Marbonne!
The benefit to growers that the French Heritage tomatoes 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.
Another excellent heirloom imitator is Pink Wonder. It resembles the beefy pink heirlooms like Rose and Pruden's Purple, with similar smooth texture and flavor uncommon to many modern hybrids.
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 4½–5½ ounces. Its distinctive dark looks, soft flesh, and savory flavor — almost as though it had been sea-salted — make it well-suited to standout branding by variety.
UHEATED Greenhouse or High Tunnel Production
The tomato varieties mentioned in the section above will also do very well in unheated greenhouses and high tunnels, but some growers find the seed cost to be prohibitive. For more "low-tech" indoor production, we often look to places like Italy and Spain for sourcing varieties. In these regions, tomatoes are grown in soil, under very large structures. The climate is hot and dry, so they don't experience leaf mold very often. They breed primarily for resistance to soil-borne diseases and viruses, as well as manageable plant habits. Resistance to verticillium, fusarium, nematodes, and TMV are so ubiquitous in these types that the term VFNT is used in the industry to describe this suite of traits. The markets these breeders serve are very fickle about fruit quality, so the flavor tends to be better in these types than in those bred for high-tech culture.
For unheated greenhouse growing, we suggest the tomato varieties detailed below. For more information on unheated protected culture tomato production and relevant disease concerns, see our Top-15 Recommended Tomato Varieties for Hoophouse and High Tunnel Production, as there is overlap in the varieties as well as the conditions of protected-culture in these various structures.
Recommended Favorites for the Unheated Greenhouse
BHN 589 — A semi-determinate slicer with great all-around performance and a low-maintenance plant. This is the variety we recommend trying first if you are getting into determinate tomato production under cover.
Estiva — Estiva has been a fixture in Johnny's catalog for a long, long time. We simply haven't found anything else with its combination of production and quality. Bred for low-tech indoor production in southern France, Estiva cranks out loaded clusters of remarkably uniform fruit in the versatile 6–7-ounce size range. The color is deep red and the flavor and texture are outstanding. Estiva is very vigorous, but the plant habit is well balanced and thus highly suitable for unheated greenhouses. Resistance to soilborne pathogens and TMV are a nice added bonus.
Clementine — From Johnny's breeding program, Clementine is a unique orange cocktail tomato that matches well with the popular Mountain Magic. Clementine features short leaves and a polite, open habit that fit well in close quarters and ventilate well.
Sunpeach— A very tasty pink cherry tomato from Japan, Sunpeach has leaf mold resistance and easy-access clusters hung on a well-behaved vine. Its unique color is perfect for mixed quarts.
Apero — Like Sunpeach, Apero is a small-fruited specialty that features leaf mold resistance and exceptional flavor. Apero also has resistance to fusarium, nematodes, and TMV, and a compact indeterminate plant.
Bolseno — Very similar to Estiva in terms of habit, disease package, productivity, uniformity, and fruit quality, the difference in Bolseno is that the fruits have a flatter shape with light ribbing, which some folks find more appealing on the farm stand. This tomato was originally selected as an Italian specialty — it can be harvested with green shoulders, like they do in Italy, but it can also be vine-ripened into beautiful crimson fruit. This is a "sleeper" variety; not everyone grows it, but those who do are very devoted!
Granadero — A broad disease package, compact plant, and huge yields of blemish-free fruits make Granadero an excellent choice for Roma tomatoes in just about any growing system, including unheated greenhouses and high tunnels. Granadero was selected specifically for performing in organic systems, so you know it's a tough customer. It features the VFNT disease package, with added resistance to powdery mildew, a growing problem in protected-culture tomatoes.
Grafted Organic Tomato PlantsFor 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.
Bell peppers are another one of the most widely grown greenhouse crops. Because 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.
All peppers will benefit from indoor growing, especially if they are being grown to the fully ripened color stage. Any of our bell or sweet specialty peppers are suitable for low-tech tunnel growing, in that they will produce higher-quality fruit than when grown in open field conditions. All perform well with a simple basket-weave trellis technique.
Peppers are far less able to overcome suboptimal temperatures than a more vigorous crop like tomatoes can. For this reason, we recommend temperature control for best results. In other words, some greenhouse heating may be required to prevent cold stress in a pepper crop.
For growers wanting to really maximize their return, there are varieties bred specifically for low-tech tunnel systems. These varieties are typically more compact, vegetative plants. Varieties that are more vegetative put more energy into the plant, a feature which helps them overgrow adversity. These include the bell variety trio, Sprinter (red), Sympathy (orange), and Moonset (yellow).
While these will perform well with simple basket-weave methods, additional labor efforts in pruning and trellising will maximize the return overall in marketable yields. For more details, see our tech sheet on 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 greenhouse and high tunnel 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.
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. It is also well adapted to stressful conditions, which can plague high tunnel growers in the cool shoulder seasons and in the peak heat of summer. Combine these features with Corinto's flavor and familiar slicer appearance, and you have a winner for protected culture.
Corinto is so productive you will need to prune fruit to one per node, to prevent the plants from becoming overloaded. To learn how, watch our tutorial Cucumber Pruning Video. For additional details, refer to our tech sheet on Greenhouse Cucumber Production, and watch our tutorial video on Lowering & Leaning Your Greenhouse Cucumbers.
For a thin-skinned, bitter free cucumber, we really like Socrates. The bitter-free fruits are so tasty that we often use this variety as our benchmark for flavor in the greenhouse trials. Socrates is very versatile, too. It can be harvested at the snacking size (5–6"), or left on the vine a little longer to be marketed more as a salad slicer, at 7–8". It does well in cooler conditions, which is a great feature for high tunnels in particular.
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 a greenhouse eggplant variety include:
- Fast, vigorous growth for high yield.
- Fruit with good flavor, appearance, and quality.
- Resilience to wide fluctuations in temperature.
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.
Aretussa is a smooth-skinned white eggplant with a slender teardrop shape and spineless green calyxes. Plants yield uniform fruit prolifically in both heated and unheated structures, as well as in the field.
These three greenhouse eggplant varieties are especially striking when marketed as a group. For cultural recommendations, see our tech sheet on Greenhouse Eggplant Production.
As a crop that prefers cooler temperatures and lower light intensities, lettuce is highly suited for winter greenhouse growing. In addition, lettuce has fairly adaptable 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.
Through extensive trialing, we have developed a well-rounded selection of high-performing lettuce varieties from our greenhouse trialing program. The following two options provide a good start.
Five Star Greenhouse Lettuce Mix. This Johnny's Exclusive 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.
Salanova® Lettuce. The Salanova line-up is another star in our greenhouse trials. To learn more about this high-yielding, versatile lettuce, see our brochure on Salanova, the Ultimate Efficiency Lettuce, or watch our video on Growing, Preparing & Marketing Salanova.
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 when we assign our Greenhouse Performer symbol to a variety, it has been carefully trialed and identified as deserving a place within the limited real estate of your greenhouse environment.