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Greenhouse tips for hoophouse growers

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This article comes from the NOFA/Massachusetts 2017 January Issue Newsletter

By Andrew Mefferd

2 Grafted plants

This article,originally published here in its entirety in Growing For Market magazine, offers some gleanings that farmer and researcher Andrew Mefferd has collected in his years of working with hoophouses both on his farm and across the continent. His new book on high tunnels, The Greenhouse and Hoophouse Grower's Handbook, will be published in February 2017. Andrew will also be co-presenting with Michael Kilpatrick, a seasoned organic farmer and consultant, at our upcoming High Tunnel intensive on Monday, February 6 at Stonehill College in North Easton, MA.

Many hoophouses are put up by growers who are more familiar with open field growing and may not employ the full range of management strategies available to make the most of protected cropping space. In this two-part series of articles, I will talk about four techniques that I think could be used profitably in an unheated hoophouse.

These techniques may involve increasing the amount of initial cost and labor that goes into a crop in order to multiply productivity. I know labor is always short on farms and many people may question why they would put more labor than they are already using into growing a crop. But protected growing space is precious real estate, and there are a lot of techniques that can help you get more out of yours. As long as you’re getting more productivity or quality out of a GH/HH space than the value of the labor you’re investing, you’re coming out ahead. Investing $5 more in labor to make $10 more is a good investment.

Variety selection

It’s winter time and you’re looking at your seed catalogs. You notice there is a greenhouse tomato section in the seed catalog, and maybe your favorite varieties are not in it. Why not just go ahead and plant your favorite field varieties in your hoophouse or greenhouse?

Well, a lot of people do, which is why I make the point that growers could benefit from at least trying some dedicated greenhouse varieties if they haven’t already. From visiting with growers I know that there are a lot of varieties (Big Beef, Early Girl, and New Girl come to mind) that are commonly grown in hoophouses though they were not bred for that. And, yes, they may do pretty well in a hoophouse. They may keep up with the yield of a greenhouse variety for a while. But over the course of a season a greenhouse variety will usually outperform a field variety.

One of the reasons is disease resistance. The other reason GH varieties will usually do better in protected agriculture is because they have been bred and carefully selected to do just that. The GH varieties that get commercialized are picked because they have performed well under the conditions including higher temperatures and higher plant densities of the GH. 

A good analogy for this would be horses.  We have many different breeds of horses each bred for a specific task. If you had a thoroughbred, you wouldn’t take it into the woods logging, would you? And likewise you wouldn’t enter your draft horse into a race. Sometimes it’s hard to see the difference without putting a few draft horses in to race against the thoroughbreds. So my advice is that if you’ve never tried dedicated greenhouse varieties, try a few plants or a row of one against your standard varieties this year. 

I’m not saying you should not grow non-greenhouse varieties in your hoophouse. I usually grow about half a house of red greenhouse hybrids, and half a house of various heirlooms every year. I see the difference when I get a third of the yield out of the heirlooms than I do out of the greenhouse varieties. But that’s a choice I’m making with eyes open, knowing what kind of yield I’m missing out on. I can count on the heirlooms getting leaf mold and stopping production late in the season when the greenhouse varieties are still chugging along.


If you only try one technique from this article, I would say the most important one is grafting. Most of the big greenhouses are already grafting their tomatoes, but when I go to smaller farms it’s hit or miss whether they’re using grafted plants. Based on my experience on my own farm and doing variety trials on rootstocks at Johnny’s Selected Seeds, I would say that grafting to a good rootstock variety like the ones that are currently on the market has the potential to add 30-50% to your tomato yields without compromising quality one bit.

It’s worth noting that you can graft other greenhouse fruiting vining crops as well, like eggplant, cucumbers and peppers, but our results with those crops have been less clear cut. You can graft eggplant and peppers onto tomato rootstocks, and cucumbers onto other cucurbit species rootstocks. But developing good rootstock/scion combinations in those crops is trickier than in tomatoes, so that’s why grafting those crops is not as common as with tomatoes. But it’s definitely worth looking at and I’m sure we’ll see more work on rootstocks for those crops in the years to come. Grafting is the kind of technique where your mileage will vary depending on the conditions.

Smaller growers generally have even more to gain from grafting. It is a generalization that obviously doesn’t apply to everyone but many smaller HH and GH growers have not optimized production conditions to the extent that larger growers have. My own HH is a good example of this. Living in Maine as I do, every single night in my unheated hoophouses, even during the summer, is cooler than ideal, and during many days in July and August the temperature is hotter than it should be. I grow in soil, so fertility for a long season crop is tricky, it’s hard to tell how much of what nutrient is available at any given time, unlike in hydroponics where you know exactly what the plant is getting because they are getting a specific mix designed for the crop. Grafting is helping me overcome the production difficulties that I face to get a 30-50 percent yield increase from grafting. Let’s break it down and look at why.

Stress resistance

The last group of benefits that rootstocks can confer on plants is the ability to thrive in conditions outside the ideal, which cause stress on the plant. Because rootstocks incorporate the genetics of wild, tougher ancestors, they can make our cultivated varieties more resistant to stress.

Especially in unheated hoophouses, plants are often outside of the ideal high or low temperature, causing thermal stress on the plant. Rootstocks are selected for resilience in the face of thermal stress, and in this sense rootstocks can do some of the work in a HH that climate control would do in a heated GH. They broaden the temperature range in which plants will thrive.

Another type of stress that rootstocks are being selected to resist is water stress - drought, flooding and salinity. This means that plants will be less impacted by any one of these hardships, making the crop more forgiving for us to grow.  Rootstocks are being developed specifically to deal with excess salinity, which could be useful wherever water is scarce and salts tend to build up, in places as diverse as Israel or Texas.

Rootstocks are also bred to resist chemical stresses, including pH being too high or low and nutrient stresses with too much or too little of essential nutrients. Wild species tend to invest more biomass into root production, so once again we see how grafting results in a superior plant where the rootstock does what it does best (root production) and the top variety does what it does best (fruit production). This superior root production includes both root density and rhizosphere exploration, which basically means that the root system is bigger and more aggressive about growing to seek out what it needs in the soil. 

I have seen the cumulative effects of all these advantages in my own hoophouses. In 2012, we had a very hot summer with many days in July and August in the high 90s and low 100s. I kept thinking that I was going to see some blossom drop, or drop in production or fruit quality due to these excessively high temperatures. 2012 ended up being my best production year so far, and I think some of that success was due to the resilience imparted to my plants by their rootstock.

All of the tips in this article mean increasing up-front costs, be they seed cost of greenhouse varieties, propagation costs of starting more plants or grafting, or labor costs of lowering and leaning the plants.  But any of these strategies that you may choose to do have the potential to increase the yield and profitability of the crop over the course of the season.  Which is one of the ways that greenhouse growers achieve such high yields—by investing a bit more money and labor in the beginning to achieve an even greater return on the structure over the course of the season.  You may not choose to do all of these things, but it is worth considering whether they may be able to help your next year’s crops.

Planting density

Another possible yield increasing strategy is how many plants you put in a given space.  I think planting density is worth thinking about because I go into so many hoophouses that have, say, five or six single rows across a 30’ wide hoophouse.  At this spacing the airflow is great but there could be a lot more plants in there!  One way to look at it is if you go into your hoophouse and there is a lot of sunlight hitting the ground, that sunlight could be put to use growing plants.  In my own hoophouse, I have emulated greenhouse spacing, with 5 double rows across the 30’ house.  I use a spacing for cukes and tomatoes with the double row two feet apart with four feet between double rows.  And I’ve seen even tighter spacing used successfully.  This has brought the amount of space used by each plant from nearly 7 square feet per plant in the first scenario to 3.5 square feet per plant in my current setup.  The sheer number of plants in there has increased yield accordingly.

There is very little light hitting the floor in my hoophouse by the time the plants have hit the top wire.  You might think the plants shading each other would reduce yield, but plants don’t have an unlimited capacity for photosynthesis, and on a good sunny day, the plants will absorb as much light as possible even with a little shading.  The thing I worried about the most when going to this heavy of a planting density was increased disease pressure with so much less airflow.  And that is one possibility but with a good leaf pruning schedule to open up airflow down low and remove diseased leaves, I have kept my disease levels manageable and greatly increased yield.

Want to learn more tips and tricks on getting the most out of your high tunnels to bolster your farm economically and supply your community with fresh high-quality products? Join us on Monday, February 6 for an intensive with Andrew Mefferd, Michael Kilpatrick, and several guest presenters. 

Learn more about the day’s offerings here.


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