The New York Times | Home & Garden | May 29, 2013 | As Ms. Doyle noted, “Home gardeners in Australia and Italy have been growing millions of grafted tomatoes for more than six years,” while American gardeners are only now discovering the benefits of grafting.
For instance, the root balls of grafted tomatoes can stretch 4 to 6 or even 10 feet wide and deep, compared with a regular tomato root mass of 2 to 3 feet. So not only are they able to find more water and nutrients during a drought, their vigor helps them deal with extended heat.
“Tomatoes stop flowering and fruiting at 86 degrees, but grafted tomatoes will continue to bloom and fruit up to 90 degrees,” Ms. Doyle said.
They also keep ripening longer, growers say, after temperatures drop in the fall.
That’s a lot to live up to.
My grafted plants looked a little wimpy sitting next to the boisterous, deep green heirlooms I had bought a few weeks ago at the Landis Valley Herb & Garden Faire, in Lancaster, Pa.
I had ordered the grafted varieties from two sources: Burpee in Warminster, Pa., and SuperNaturals in Vista, Calif. Both sets were carefully packed and green, if a bit bent over from their shipping. But that’s to be expected from any plant that is put in a box for a day or two.
They all looked a bit fragile at the graft union, where the scion meets the rootstock, and I could imagine them snapping off in a big wind or thunderstorm. So after I planted them, I used a piece of soft twine to tie each stem to a little bamboo stake sunk in the ground.
Finally, about planting a grafted tomato or any grafted plant, for that matter: It is crucial to keep the graft above the soil line so that the scion does not root into the ground. Tomatoes are notorious for their ability to root along the stem, which is why I often bury mine up to their necks — or even place leggy ones into a horizontal trench, with just the tops showing above ground — to develop a sturdy root system and a bushier plant.
That doesn’t work with grafted tomatoes.
If the scion, say, of my grafted Brandywine roots into the soil, the whole plant can lose the disease resistance of its hearty rootstock. So I made sure to keep the graft about an inch above the soil. And I will have to watch it carefully as it grows, keeping any vigorous vines from lounging on the ground, because they, too, will take root.
“Cage it, or put it on ropes or a fence, to keep it off the ground,” Ms. Doyle said. “Or it will root in.”
So keep the plant pruned up a bit. And for heaven’s sake, don’t let the bushes ramble all over the ground. That’s curtains for a grafted tomato.
Now I have a grafted Brandywine and a grafted Mortgage Lifter growing next to their ungrafted counterparts, as well as a few other grafted varieties, like San Marzano, Pineapple and a purple-red tomato called Indigo Rose. Developed by Jim Meyers, a breeder and professor, and his students at Oregon State University in Corvallis, Indigo Rose contains germ plasm from two wild species, from the Galápagos and Chile, which both produce anthocyanins, compounds that are powerful antioxidants.
“The antioxidants are dramatically increased, primarily in the skin,” Professor Meyers said. “Anthocyanins don’t affect the taste — they taste just like any other tomato.”
But you have to let them ripen fully, he said. The purple skin can hide unripened fruit.
“The fruit has to get soft, and on the bottom of the fruit should be a nice deep red,” he said.
Professor Myers knew that Indigo Rose was susceptible to verticillium and fusarium and nematodes. “I thought grafting was a way to get around that,” he said. The grafted plants were also more vigorous, providing three times the yield of ungrafted plants.
Still, not everyone is convinced.
Eliot Coleman and Barbara Damrosch grafted their own tomatoes for a few years at Four Season Farm in Harborside, Me., and then gave up.
“We didn’t feel that it made that much difference,” Ms. Damrosch said. “Crop rotation, using movable greenhouses and making staggered plantings have remained our best strategy.”
Mr. Coleman said he simply found them “a little weird.”
And Carrie Engel, the retail greenhouse manager of Valley View Farms in Cockeysville, Md., was kind of ho-hum.
“People aren’t going after them,” said Ms. Engel, who still has Mortgage Lifters and Brandywines on her shelves. “It’s not that big a deal yet.”