How to Select Vegetable Varieties for Greenhouse Growing

Posted by Michalina Hunter on June 04, 2021

How to Select Vegetable Varieties for Greenhouse Growing

Got a new greenhouse or poly tunnel and wondering what varieties to plant? Experiencing issues with low yields or disease in your greenhouse? Check out this interview with Gemma McNeill, Owner-Operator of Zaklan Farm, a suburban microfarm in Surrey, British Columbia. Once you’ve gleaned some wisdom from Gemma, you may want to learn more. We recommend you follow up by reading an outline on how to select vegetable varieties for greenhouse growing, plus recommendations for the best greenhouse tomato, pepper, cucumber, eggplant, and lettuce varieties to try, from Johnny’s Selected Seeds.

Photo above is of Gemma by Zaklan Farm.

Greenhouse Growing at Zaklan Farm

Zaklan Farm is a 1.5-acre market garden in the Lower Mainland of British Columbia that is doing amazing things and growing new farmers! We caught up with co-owner/farmer Gemma McNeill to learn about her experiences variety testing for their greenhouses to find out what works in their context.

“A greenhouse is some of the most expensive and valuable space you have on the farm,” says Gemma. “Maximizing that is important, as well as knowing your market. Tomatoes are a super high value crop, and one of the most labour-intensive you’re going to grow. Tending that crop every week from February to November is a huge investment. We have a few greenhouses which are great for rotating crops, and for growing things in the shoulder season to even out your yearly income and sell when the demand is high.”

How to Select Vegetable Varieties for Greenhouse Growing
Gemma packing tomatoes at Zaklan Farm

How Zaklan Farm Found What Tomato Varieties Work Best for Them

“I feel like we’ve grown every variety of tomato,” Gemma laughs. “We did a lot of trial and error in our first years to find what we like and our customers like. We tried heirlooms and cherries and more. We found heirlooms were not high enough producing and didn’t have enough disease resistance. Our greenhouses tend to have high humidity and tomatoes were prone to early and late blight. So now we’re selecting varieties that are resistant.”

“Consistency is really important. We work with a lot of chefs, and many heirloom varieties tend to have more catfacing and splitting, which decreases the value of the fruit and may require some to be tossed. Our customers are paying more and want to be able to use the whole fruit without cutting off split or damaged parts.

“We grow mostly hy-looms now (essentially hybrid versions of classic heirlooms). People can’t tell the difference in flavour between heirlooms and hybrids, and there is so much more to it that the farmer needs to take into account such as texture, post-harvest handling, etc. For example, chefs love green zebras, but they don’t yield enough to be worth growing. We found a higher-yielding alternative (Marvori) that we now grow instead. We’ve been exclusively growing Johnny’s French Collection for the last two years, and are trialling some others. We always have room for trials!”

Grafting Tomatoes, Cucumbers, and Eggplant

“We did grafting trials with different types of rootstock to figure out was was worth it labour-wise,” says Gemma. “Grafting larger tomatoes makes sense, but not for cherries.

“We’ve grown many cucumber varieties with varying success and trying to find markets for them,” says Gemma. “We only grow Katrina now, a Persian cucumber. We used to grow field and English and Japanese cukes, picklers, etc. but we weren’t making any money off cukes. Grafting makes a huge difference. Now we graft all our cukes, and just do one sowing. It helps with vigour in the cold soil of an unheated greenhouse, and with disease resistance and productivity.

“We are now grafting eggplants onto Johnny’s DRO141TX tomato rootstock with amazing results. We did a trial last year, and the grafted plants just took off compared to the non-grafted ones. Production is bigger and longer throughout the season.”

Check out Zaklan Farm’s Youtube video on grafting tomatoes, cucumbers, and eggplants!

How to Select Vegetable Varieties for Greenhouse Growing

A Note on Greenhouse Sanitation

Gemma notes that “really good sanitation practices are super critical. We have hydrogen peroxide bottles in all our greenhouses and staff are trained on sanitizing pruners between plants, and flagging any plants that may have disease. I have no qualms about pulling plants if necessary.”

Advice for New Growers

“With new growers, you think you have to grow everything. Get a mentor to narrow down what to grow! We have a great community of farmers to nerd out with on varieties too. Instagram is also a great way to see what other folks are doing. Ben Hartman is amazing about sharing info online. Also, use your Seed Reps! In our first years it was intimidating to reach out to them, but those are important relationships, and it’s their job to help you. We email our rep a lot!

“Now in our 9th year, I know what sells, what makes a difference, what we are good at and not good at. It all comes back to record keeping!”

By way of the above interview with Gemma on considerations required of greenhouse growers, here is a more in-depth introduction from Johnny’s to what to look for when selecting varieties for greenhouse growing.

What Makes a Variety Right for the Greenhouse?

Johnny's Research Team Evaluates the Greenhouse Trials
Collecting trial data at Johnny’s Research Farm. Image courtesy of Johnny’s Selected Seeds. All rights reserved.

Greenhouses and poly tunnels of every conceivable shape, design, scale, and technology are cropping up everywhere, as growers around the globe discover the advantages of protected culture. Of the innumerable benefits of greenhouse culture, season extension, better yield and quality, and protection from adverse weather and pathogens such as early and late blight top many growers’ lists.

Growing within a protected environment does carry its own set of challenges, however, including space limitations, more exacting requirements for the right variety/nutrient/light/irrigation recipe, the demand for 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.

Above & Beyond Flavour — What Johnny’s Looks For

Johnny’s research team conducts variety trials at their research farm in Albion, Maine, and in cooperation with growers and university researchers across the globe. Just what are they looking for when they trial varieties in protected culture? Above all, they want varieties that taste good. With that as the starting point, they look to identify a variety as a good choice for protected culture if it excels in one or more of the other qualities listed below.

  • Flavour — Always tops Johnny’s list.
  • Vigour — To keep growing longer than the season would require for field production.
  • Plant habit — The space limitations of indoor growing favour 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 greenhouse/hoophouse structure.
  • Ability to do well under low-light conditions — Examples include red lettuce that develops its full pigmentation potential or sunflowers that are daylight-neutral. Or, they may look to see whether a variety escapes disease or physiological symptoms characteristically heightened for the crop when light transmission is restricted by glazing material.
  • Ability to set fruit without pollination — A greenhouse enclosure limits flowering crops’ access to pollinators such as bees and butterflies. This can be especially critical for cucumbers grown indoors, which is why parthenocarpic varieties are often recommended for indoor culture.

To read the rest of the article, visit Johnny’s Grower’s Library…

Greenhouse Symbol

And when you’re looking for varieties that are right for the greenhouse, remember to look for Johnny’s little greenhouse symbol. It signifies varieties that clearly and consistently demonstrate outstanding performance in their protected-agriculture trials!

We hope you enjoyed this article! Thank you, Zaklan Farm. Make sure to check out the informative articles, guides, webinars, and tools offered in Johnny’s Grower’s Library. And check out Zaklan Farm’s website and social channels!

Looking to connect with a seed rep? Contact Molly Sadowsky, Johnny’s Commercial Sales Rep for Canada at

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