by Sonja Heyck-Merlin

A group of Northeast growers shared tips on tomato grafting in a webinar presented by the New Hampshire Vegetable & Berry Growers Association (NHVBGA) and UNH Extension. Grafting tomatoes requires three steps: Growing healthy rootstock and scions in the pre-graft stage, grafting and post-graft plant healing. Although the techniques used by the growers in the webinar vary, they have a common goal – to combine desirable fruit characters with a robust rootstock to produce transplants with disease resistance, stress tolerance and high yields.

Tasha Dunning: Spring Ledge Farm, New London, NH

“I have been grafting for about 25 years,” said Dunning. “We had tomatoes in the same house for 20 years, and they were not growing well. We started grafting, and it was incredible.” Dunning currently grafts about 3,000 tomatoes per year.

Dunning uses an eight-foot-wide by three-foot-deep heated chamber equipped with lighting to germinate scion and rootstock seeds. The chamber has four shelves which can hold 16 trays each. She plants scions and rootstocks into 98-cell seedling trays. Once they germinate, they are moved to a heated greenhouse for about three weeks. Dunning then grafts, always in the shade, transitioning the plants into 48-cell seedling trays. Finally, she moves the transplants back into the chambers for the post-graft healing process.

The chambers are wood. Dunning said she wishes they had constructed them from plastic because “the wood grows algae like crazy.” Because of this, she spends significant time cleaning and sanitizing. As the grafts are taking, they use misting nozzles on an automatic timer to maintain soil moisture and humidity levels; the nozzles water for approximately one second every 25 minutes. In Dunning’s opinion, the optimum ambient temperature for the chambers is 75º F. To achieve this, she uses greenhouse heated bench tubing hooked to a thermostatically controlled hot water boiler. In former iterations, they used incandescent light bulbs to generate the heat.

“Having everything programmed is really nice because we can throw the plants in there, walk away for seven days and pull them out. They have light, so they can stay in there a little longer than a dome system where it’s total darkness,” Dunning said. She always puts the grafted plants into the greenhouse late in the day, so they have a night to adjust to the low humidity before they are exposed to the sunlight.

In addition to the automation, Dunning appreciates the ability to use the chambers to control the size of the scions and rootstocks in the pre-graft stage. When the scions and rootstocks aren’t matching, she can place one or the other into the chamber to either speed or slow down growth. “You can really finagle things and get the plants to match,” she said. The farm also uses the chambers for germinating other seeds, to promote growth on unrooted ornamental cuttings and to grow microgreens.

Andre Cantelmo: Heron Pond Farm, South Hampton, NH

Cantelmo grafts about 10,000 tomatoes per year for production and for sale. He seeds his rootstocks two or three days before the scions, using 98-cell seedling trays. Because he said he is “only physically capable of doing 400 grafts per day,” he staggers the plantings over a period of three weeks. The variation in sizes also gives him options when it comes time to match the diameter of the scions and rootstocks. Two days pre-grafting, he tries to slow the plants down by moving them into a darker, shaded area of the greenhouse.

For rootstock, Cantelmo primarily uses DRO141TX. “I have found that it helps me keep my plants in more of a regenerative mode rather than a vegetative mode,” he said. He uses silicone grafting clips, preferring to graft when the plants require a 1.7- or 1.8-mm clip.

Like Dunning, he starts the scions and rootstocks in a greenhouse, but moves the grafted plants onto shelves in a dark, insulated closet in his basement. The closet is heated with a portable oil heater. Once they’re on the shelves, he covers the trays with tall plastic domes. To create humidity, he simply removes the domes, spritzes the plants with a spray bottle and then returns the covers.

Once the grafts take, Cantelmo removes the domes and transitions the plants onto additional basement shelving equipped with LED shop lights. He leaves them under the lights for a few days before transferring them to the greenhouse. Formerly, he moved them directly from the heated closet to the greenhouse. “With this system, they seem to be doing much better,” he said.

Cantelmo acknowledged that he would like to upgrade his system but said that his current system is very functional and successful. In his opinion, with a simple warm, humid and damp space, growers don’t need to spend a lot of money to get started grafting. “You can do a lot with something as cheap as this,” he said.

Tim Livingstone: Strawberry Hill Farm, Pembroke, NB, Canada

Livingstone introduced an unfamiliar post-grafting trick to the webinar participants: As soon as the grafts have taken and the plants begin to grow, he pinches off the top of each plant, leaving only the two cotyledons. The effect is that the tomato plant will produce two heads. “To do this, it’s important when you’re grafting to make sure the rootstock is grafted below the cotyledons,” he said.

According to Livingstone, within two day you get two heads split out of each cotyledon. They are the same size and grow equally. “You only need half the amount of plants,” he said. “It compensates for the extra expense of seeds.”

Livingstone grows three rows of tomatoes in the high tunnels – on the edges he uses single head grafts, but in the center row he plants the split heads at 16 to 25 inches apart, depending on the variety.