Choosing high tunnel tech that works for you
by Sonja Heyck-Merlin
Dave Chapman, owner of Long Wind Farm in East Thetford, VT, was the main speaker in the first of a three-part webinar series titled “High Tunnels After Dark: 2020 High Tunnel Production Conference.” The series was a collaboration between Maine, New Hampshire and Vermont Extension Services.
Chapman’s presentation was “Low Tech Tunnels to High Tech Greenhouses: Choosing Technologies That Work for You.” Chapman grew up on a dairy farm in Pennsylvania and has been farming in Vermont since the 1970s. He currently grows 2.5 acres of certified organic tomatoes in fully automated glass greenhouses. The tomatoes are planted directly into the ground. No tillage is used in the greenhouses.
Of his experience with growing in high tunnels, Chapman said, “It has spanned from an unheated tunnel with a single sheet of plastic to double-ply with two-by-six framing to metal hoops, and now to glass gutter-connected greenhouses.” Because of his range of experience with high tunnel production, Chapman presented practical tips for all producers.
He said one of the goals for any kind of greenhouse production is to attempt to have everything as even as you can, including temperature and soil moisture. “Anything that becomes uneven costs you in production and yield,” he said. In particular, the edges of tunnels tend to be cold, and Chapman suggested burying plastic tubing and circulating warm water, heated with a simple domestic water heater, through the tubing. “Of course, it can get complicated if you have to worry about freezing, but we made it work back when we did that,” he said.
Chapman emphasized the importance of compost in tunnel production. “In order to keep a high level of biological diversity in our soil, we bring in a lot of compost. Our soil is teeming with life and worms,” he said. Although he grows tomatoes in the same soil year after year, he said he has no root disease or salt build-up. Over the course of a 10-month growing season, he spreads a light dressing of compost over the soil surface every four weeks. No surface plastic is used in the greenhouses because it would inhibit the ability to spread the compost.
He also advocated for the use of grafted tomatoes plants in high tunnel production. He used to think that grafting was only necessary to prevent disease in an environment where tomatoes are being constantly grown. However, he experimented with growing tomatoes in virgin soil and observed more robust growth in the first four trusses. “With grafting,” Chapman said, “you get strong plants that grow more quickly, even in the beginning.”
A piece of grafting advice from Chapman is to skip every other hole in the plug trays to protect plants from humidity. He also said that once the rootstock and top are grafted, the plants should be placed in a tent. His tents are made from press-fitted PVC pipe covered with plastic. For the first few days, the overhanging plastic should be tucked around the plants and the top of the tent should be covered with rigid foam board to shade the seedlings. For optimal survival, the temperature should be about 74º. On day three, Chapman said to cut some slits in the plastic to begin letting in air. On day four, he rolls up the sides a few times for half an hour. On day five the sides are rolled up, and the next day he removes the plastic.
Chapman recommended keeping watering to a minimum while the grafts are taking. The goal is to have the plugs totally wet prior to grafting so they go into the tent completely saturated. He said that if the plants in the tent are looking dry, he will mist them on day two, and then water them on day four. Chapman also noted that grafting adds a week to the babyhood stage of raising tomato seedlings, so growers will have to adjust their planting schedules accordingly.
Once the grafted plants come out of the tent, they are moved to pots. At Long Wind Farm, they top each plant above the cotyledons so that each plant has two leaders. Chapman noted that if growers want to use this practice, they should plan to adjust their planting schedule by another week.
“Another principle we pursue in our greenhouses is to think about setting up so everything is on wheels,” Chapman said. The pathways in his greenhouses are equipped with pipe rail. Carts are placed on the pipe rails, making it easy to move supplies and plants up and down the rows. During harvest, workers can sit on a cart and slide themselves along as they pick. The pipe rails serve another purpose at Long Wind – they contain circulating hot water, which heats the houses. While these technologies are beyond the scope of many smaller growers, Chapman stressed that over the long term, they can reduce a significant amount of labor.
In closing, Chapman shifted the conversation to the business side of farming. He said, “The most important question growers must ask of ourselves is if the biggest constraint we face is in production or marketing.” In his experience, the answer for most growers is the marketing.
“I have seen a lot of tunnels and greenhouses with rotting tomatoes in them. It makes you wonder if someone should have grown half as many and half of something else. It is important for growers to understand if their problems have to do with marketing or have to do with growing food efficiently,” Chapman said.