by Sanne Kure-Jensen
Skip and Silas Paul of Wishing Stone Farm in Little Compton, RI have been grafting tomatoes for over ten years. Like other greenhouse growers who graft tomatoes, Skip started because of production problems — largely due to growing tomatoes in the same greenhouses year after year. Diseases like Corky Root Rot eventually reduced yields and shortened the productive lifetime of the farm’s tomato plants. Wishing Stone Farm grafts tomatoes for their own use and sells about 4,500 grafted tomato plants to other greenhouse growers.
The Pauls use Maxifort rootstocks that offer disease resistance and exceptional vigor. The top three ordered scions are Geronimo, Rebelski and Trust. Geronimo and Rebelski offer the highest yields in pounds per plant. Skip’s personal favorite tomato is Purple Cherokee. Silas’ favorite tomato is an heirloom called Great White.
Customers love Wishing Stone Farm’s exclusive heirloom tomato selection called Sumosan. It looks like a pink Brandywine but tastes much better, according to Skip.
Skip advises growers “use your taste buds first and the seed catalogs last! Big Beef has seen a big resurgence in the last year! It costs one-tenth the price of Geronimo! Decide for yourself!”
Successful tomato grafting requires meticulous planning and preparation as well as careful post graft plant care. The actual grafting process is simple. Light intensity, greenhouse temperature and humidity levels will vary from January to April.
Wishing Stone Farm uses only fresh seeds for the earliest seedlings started in mid-January. By mid-February, new or one-year-old seed can be used. The first seedlings started are the rootstock plants. Maxifort is a wild hybrid tomato from Thailand and consistently has some delayed emergence issues. Two days later the scion plants are seeded. Sixty percent of Wishing Stone Farm’s tomato production uses Geronimo. Geronimos are seeded in quarter-tray batches daily.
Silas uses top grafts not side grafts. On graft day, the rootstock and scion widths must match. With hundreds of grafts to be done, having staggered plantings allows for well-matched plants. For insurance, the farm starts 15 percent extra plants to allow for size matching.
The Pauls recommend using a new, sanitized razor blade. Be sure to sanitize after every ten cuts.
Silas and Skip urge growers not to over nourish plants. Some purplish or light green leaves are fine. Their seedlings will not receive any supplemental plant food. They take advantage of the innate fertility of Vermont Compost Company’s Forte Lite soil mix. Wishing Stone Farm uses Root Shield and other plant/seed protectants.
Bottom heat up to 73 degrees F is essential. The Pauls recommend double-checking mats for hot spots. Too much heat can be worse than temperatures below 70 degrees F. Overheating stimulates stretching. The Pauls built a covered box around their heat tables to eliminate nighttime drafts. The sides roll up to avoid overheating during daylight hours. A bit of artificial light can be helpful during long cloudy periods.
Match the graft clip size to the plants’ diameter. The Pauls use new #2.0 or larger clips made of plastic tubing, though 1.2 and 1.5 grafting clips are also available. If the smaller ones fit, Skip said, “the plants are probably too small and too young.” Sanitize the clips before use. Leave the clips on until they pop off on their own.
The day before grafting, Silas sorts the plants by stem diameter into two-lane trays. New 98-cell trays were cut vertically into two-row sections and then sanitized. The two-lane trays hold the plants upright and stable during grafting. The two lane trays allow Silas to work down each line of plants without disturbing any previously grafted plants.
From the day before grafting, the plants should only receive bottom watering. Keeping the stems and leaves free of liquids reduces impurities and disease risks. Blend Oxidate with bottom watering liquid and sanitize all trays. Maintain 400:1 concentrations for sanitation.
Silas routinely trims some leaves from the scions plants. Be careful to lessen the leaf load on the plant but still create a need in the plant to suck up nutrients from the rootstock. This will urge the tissues to connect and heal. Immediately after grafting, put two-lane strips into a solid 10” by 20” tray and cover with a high dome cover misted on the inside for ample humidity. Place the domed tray and plants in a darkened, heated area at a stable 78 degrees F with 95 percent humidity. A low light level — close to 85 percent shade — is critical at this stage. Mist the inside of the dome, not the plants, several times each day and once more late at night. Do not let the temperature spike, as too much heat will stress the plants during their healing process. Wishing Stone Farms buys high dome covers from Fabrique Par Optimum Hydroponix, Quebec, Canada, www.hydroponix.com; 800-489-2215. Another source they use is Green Trees Hydroponics in Vista, CA: www.hydroponics.net; 760-598-7551.
Silas recommends growers perform tomato grafting after 2 p.m., especially on sunny days, to reduce plant stress. Results will be better and plants will take faster if you wait until afternoon.
Pay attention to moisture, heat and light for the next three days. Do not worry if the scion droops a little.
After three to five days, move the grafted plants into a second recovery area with diminished light. Keep the domes on and gradually start opening them. Slowly acclimate the plants to the new greenhouse environment and gradually reduced humidity.
Avoid sudden changes in light levels during these final adjustment days. If you move your plants from the first recovery room under cloudy conditions, be cautious about the effect of bright sunlight. Beautiful, healthy plants can be killed by too sudden a change in light level or a shift to hot, dry air in sunny greenhouse in March.
For more information, email Skip Paul at firstname.lastname@example.org or visit or write Wishing Stone Farm at 25 Shaw Road in Little Compton, RI.
Grafting tomatoes for commercial grower use
by Sanne Kure-Jensen