I say tomato, you say potato

Grafting veggies yields interesting new combos

If we think biotechnology was invented in the 21st century, consider the somewhat bizarre practice of sticking the top of one plant onto the bottom of another: Grafting, this is called, and it’s been around for at least 4,000 years.

Those ancient Greek and Chinese gardeners knew the right match could produce a plant greater than the sum of its parts — the roots of the first would make the leafy second more vigorous and fruitful.

Many of the woody plants in your garden are grafted — that weeping cherry tree now blooming, for example — but the idea of growing grafted vegetables at home is new in North America, with the first plants arriving five years ago in limited markets. It is still too soon to tell whether this is a passing fancy or here to stay, though mail order catalogues and garden centres are betting on the latter. With each passing spring, they are increasing the quantities of grafted plants and the number of varieties.

The main focus of this phenomenon is the tomato, but consumers will also find grafted peppers, eggplant, cucumbers, cantaloupes and watermelons.

“We went from zero [grafts] in 2009 to over a million this year,” says Alice Doyle, who, with partners John Bagnasco and Tim Wada produces and distributes vegetable grafts to wholesale growers and farmers under the brand SuperNaturals.

This year, the enterprise is offering a line of plants that will yield two varieties on one rootstock and a true Frankenstein plant that promises trusses of cherry tomatoes on top and a bed of potatoes below. It is being marketed as Ketchup ’n’ Fries.

Beyond the novelty value, why would gardeners grow grafted veggies?

Various rootstock hybrids have been developed to bestow different traits, including resistance to a slew of diseases that afflict such popular plants as tomatoes, including blight and wilt pathogens. Rare is the tomato patch in the mid-Atlantic area that doesn’t have early blight, where leaves yellow from the bottom up and plants can become not just unsightly but feeble if the gardener doesn’t stay on top of it.

Grafts are particularly useful for gardeners who don’t have the space to move plantings from bed to bed annually. Tomato plants grown in the same soil each year will perform fine for four or five years but then will take a tumble as diseases and pests build up, says Steve Dubik, a professor of horticulture at Montgomery College in Rockville, Md.

Grafted plants can also achieve other miracles, such as producing more fruit, extending the harvest period and even tolerating hotter or colder climes. The selling point for heirloom varieties such as Brandywine or Mortgage Lifter is that grafted versions fix the general problems associated with antique varieties: poor yield and disease susceptibility. The University of Maryland found the yield of grafted Cherokee Purple tomatoes increased 25 per cent.

Chelsey Fields, the vegetable product manager for W. Atlee Burpee & Co., said heirlooms tend to have been developed or discovered by gardeners in a specific locale and may be ill-suited to other regions, climates and soils. “They aren’t necessarily as adapted nationwide as people would like them to be. The thing with grafting is that it really makes them adaptable to all these different environmental pressures,” she says.

Burpee started selling grafted tomatoes in 2012 and now has a dozen tomato varieties for sale and more in the works, Fields says. “Last year, I dropped Yellow Pear and added in Mr. Stripey, Green Zebra and Marglobe based on garden performance,” she says. This spring, Burpee added three pepper varieties and an eggplant to its catalogue.

The downside to grafted veggies, apart from their added expense, is that their garden performance may not be as dramatically different as billed, and in some cases it’s worse because the highly efficient root system may produce lots of moisture to the fruit but at a cost to flavour.

Jeff Gillman, a horticultural instructor at Central Piedmont Community College in Charlotte, N.C. conducted field trials with students and found that when the growing conditions were optimal, the non-grafted tomatoes actually fared better than the grafted ones. In difficult conditions of poor soil and inadequate irrigation, he found that the grafts were superior.

“I entered the experiment skeptical, and I left convinced I would try grafted tomatoes if I were to grow them in a difficult situation,” he says.

Grafted vegetables “may not be a huge advantage to all gardeners,” Dubik says, “but for those gardeners who have to plant the same spot year after year and the disease pressures build up, they don’t have a lot of options.”

Grafted plants differ in another fundamental way. Tomatoes are typically planted deep to encourage more root development along the lower stem, but the union in a grafted plant must be kept above the soil line to prevent the scion from sending down roots and negating the benefits of the rootstock. Also, the plant must be supported and kept from sprawling so that stems do not touch the ground, where they would also put down roots.

And then there is cost. A grafted plant might sell for more than double a conventional transplant.

But fixating on the cost or even the results of grafting may be missing the point: Gardeners like novelty and find delight (and frustration) in observing and growing new things. “It’s a little bit of a fad but relatively easy,” Dubik says. “I think a lot of people are going to get into it and stick with it.”