Well, not exactly, but heirloom tomato varieties grafted to hybrid nematode-resistant rootstock can be more productive. The grafting is easy, but the transitioning is a bit tricky because there’s no dormant stage with tomatoes. Since it takes 2-4 weeks longer than the usual 6-8 weeks to get grafted tomatoes ready for the field, Dec/Jan is the time to start seeds if you have a greenhouse or fluorescent lights that you use to start your own tomatoes.
First decide on a hybrid rootstock—any variety with nematode resistance is a potential candidate. Celebrity, Better Boy and Big Beef are some that have been used. There are specialty rootstocks available from Johnny’s Seeds, but the seed is expensive and some varieties may not be nematode resistant. Start your heirloom and rootstock seeds at about the same time. You may find that the hybrids grow faster so starting the heirlooms about a week earlier is an even better plan. Use a good soilless potting soil, and a bottom heating cable designed for seed starting will get them up faster. In the home under lights, putting the seed flat in a plastic bag or covering it with plastic wrap will keep the soil from drying out too fast.
A single edge razor blade is perfect for the grafting cuts, but you can use any sharp, thin-bladed knife for the job. Plants should be about 3-4 inches tall and 1/8 inch or less in diameter when you perform the surgery. Some folks recommend a straight cut on the rootstock (typically 1 ½-2 inches above the soil) followed by a straight downward cut, centered in the middle of the cross-section cut you made to prepare the rootstock to accommodate the heirloom top. Make sure to cut so that the top (heirloom piece) and rootstock are about the same diameter. The cut on the scion (heirloom piece) is made with a long, sloping, axe-like bevel that will slip into the cut in the rootstock—essentially a cleft graft. Cut it loose first then make the axe-like cut—it’s easier to make a uniform cut this way (If you didn’t look at the Johnny’s Seeds website for rootstock, you might want to check out their info on tomato grafting including diagrams). This technique does create some strength and lots of cut surface contact. Pros like my buddy Tom LeRoy make straight cuts on both pieces and then make sure they are touching when they are inserted in the clip or tubing—they won’t jump the gap! Johnny’s has the little clips you may want to use for holding the grafted stems together though you can substitute a ¾-1 inch piece of aquarium tubing with 1/8 inch inside diameter to hold the pieces together. Be sure to first cut the tubing lengthwise through one side with a single-edge razor blade so you can remove it allowing the stem to expand in diameter.
Now for the tricky part. Water the rootstock soil thoroughly and place the pot with heirloom graft in place into a plastic bag large enough to seal without bending or disturbing the delicate graft. This usually necessitates a one gallon bag. Sprinkle a little extra water into the bag and carefully seal it. Now put the bags in a dark closet or a dimly lit room for at least two days. This gives them time to heal and the high humidity will lessen the chances that the top will go into a permanent wilt condition. Gradually bring the grafted plants out to more light. It may be a week before they can benefit from some morning sun and you will need to open the bag and mist the plants every day or so. After a week to ten days begin to leave the bag open and watch for wilting. If the plants remain turgid you’re off to a good start.
If you have a small greenhouse go with the dark closet for two days and then locate the plants under a bench or make a shaded area with lath or black plastic (over the top only). Humidity will be higher in the greenhouse so you can begin to open the plastic bag after a few days and mist the area 4-5 times per day. Of course the greenhouse needs to be warm but not too hot—70’s would be best but 80’s are tolerable. A bottom heating mat at night would be nice but once tomatoes are up they rather enjoy cool temperatures. When plants seem to resist wilting it is time to get them out of the bag and gradually move them to a sunny bench. Try this for a few hours in the morning, but if wilting occurs even though the plants are misted and the soil watered, move them back into the shade for a few days. A greenhouse with an intermittent mist system will really speed up the healing process but if you’re this advanced you could likely help me write this blog.
Once the plants are growing vigorously, fertilize once or twice weekly until temperatures are consistently above freezing at night before you put them in the garden. Usually March 1 is a good target date for the average last frost in the Houston area. One more caution—you don’t want the rootstock to sprout competing shoots—they can take over and you also don’t want the top to develop roots—these roots will be susceptible to nematodes. A small bamboo stake is generally adequate to keep the plant growing at the same height above the soil line. This is one time you don’t want to plant a little deep and let the stem produce roots.
Commercially grafted tomatoes are becoming available. We tried a Cherokee Purple Mighty ‘Mato last year and it made a large, very productive plant. It didn’t last into the fall though. Since the rootstock they use is their secret, I’m not sure how much nematode resistance it has. They do claim resistance for Mighty ‘Mato roots but resistance is just resistance, not immunity.
In case you’re still not convinced to give grafted tomatoes a try, a North Carolina study showed a 23% increase in yield with Cherokee Purple on Maxifort rootstock (one of the specialty tomato rootstock varieties). P.S. — be careful with the single-edge razor blades!