Grafting greats

From increased vigor to improved resistance to disease, grafted vegetables are proving highly valuable to nearly everyone in the produce supply chain.

Every now and then, something comes along that is truly innovative. The automobile and smartphone come most readily to mind. In the world of gardening and agriculture, it may just be the grafted vegetable.

Grafting vegetables is nothing new. It’s been done in Asian and European countries for centuries. It has only been practiced in the United States for about the last five years, however. Tomatoes are getting most of the attention at the moment, but other vegetables are starting to be grafted and sold to gardeners and market growers alike.


Building a case
Grafted vegetables not only create an opportunity for growers, seed suppliers and retailers; they may actually become a necessity as growers everywhere struggle with soil-borne pathogens such as verticillium, fusarium wilt, corky root rot, root-knot nematodes, bacterial wilt and southern blight.

There are many other benefits to grafting vegetables besides the incredible disease resistance that wild rootstocks provide, according to Alice Doyle of Log House Plants in Cottage Grove, Ore. In the case of tomatoes, grafting results in increased vigor, enabling the plants to start better in cool climates and grow well into fall, she says.

Chelsey Fields, vegetable product manager for W. Atlee Burpee, agrees. “One of the benefits is you can go into a little cooler soil, start them a little earlier,” she explains.

Grafted tomato plants also do well during the heat of the summer, still setting fruit when the temperature hovers around 90 degrees, Doyle says. This is unlike seed-grown tomatoes, which stop initiating flowers at 86 degrees. Grafted plants also tend to bounce back after a drought, while seed tomatoes continue to languish from the heat. Heirlooms, which are particularly susceptible to soil-borne disease and struggle to ripen in the northern climates, will particularly benefit from being grafted, Doyle says.

One thing everyone will love about grafted tomatoes is their incredible crop yield, says John Bagnasco, president of GardenLife and co-host of a national radio show that offers gardening advice and introduces new vegetable varieties.

“We do trials all over the country,” he says. “We trialed Indigo Rose, a variety developed by Oregon State University.”

Indigo Rose is a tomato highest in antioxidants and is traditionally bred with a wild species from the Galapagos Islands. “We grafted the Indigo and had great results, three times the weight and three times the fruit,” Bagnasco says, adding that grafted tomatoes will produce at least double the amount of tomatoes as seed-grown plants.


The grafting process
Grafting vegetables is a process that involves joining a scion to a hardy rootstock. This is done in a clean, environmentally controlled greenhouse or in a lab. Many growers, like Joelene Jebbia of Gathering Together Farm in Philomath, Ore., say they use inexpensive covered chambers to trap in the humidity while the graft union forms. Jebbia’s farm grows grafted tomatoes in the ground in high tunnels for the fresh vegetable markets it serves.

“We started out not knowing anything about grafting tomatoes,” says Jebbia, who is now producing 6,000 to 8,000 grafted plants per year. “Read everything you can about it. YouTube offers some good videos on grafting vegetables.” Among other things, the YouTube videos show different types of grafts, such as the side veneer and splice, and options for clips to hold the scion and rootstock together until they fuse.

All the tomato varieties we enjoy eating in the United States, be they hybrid, heirloom or open pollinated, are of the same species, says Doyle. The rootstocks currently being used for grafting are hybrids of wild species that can’t produce an edible tomato but do have important innate disease and soil-borne pest resistance. What’s more, they can be grafted to any type of tomato.

Growers have differing opinions on what the best variety of rootstock is for grafting vegetables, but all agree it should be a generative rootstock — one that produces prolific buds and fruit — as opposed to a vegetative rootstock that produces a lot of foliage and fewer buds. The latter can be a particular problem for greenhouses and high tunnels (as well as the home gardener), so it is particularly important to use generative rootstock in these growing situations.

Mark Willis of Harris Seeds grafts plants for his company’s mail order business. He says they’ve tested the Maxifort and Beaufort, two popular tomato rootstocks that may be too vegetative for the home gardener. Right now, he is grafting with the RST-04-105-T tomato rootstock. He says he allows the grafted plants to fuse in a clean lab that is equipped with the usual environmental controls found in a greenhouse.


A rock star rootstock
The rootstock that appears to be sweeping the country is SuperNatural, which is the choice for Plug Connection’s 39 grafted varieties that comprise the Mighty ‘Mato line of tomatoes. SuperNaturals Grafted Vegetables LLC/Plug Connection is the largest producer of grafted young vegetable plants in the United States, says Bagnasco. They also graft other plants that carry the Mighty Veggies label, so be on the lookout for grafted eggplant, peppers, cucumbers and melons. Growers and gardeners can also purchase SuperNatural rootstock and seed from www.territorialseed.com and www.awhaley.com.


Retail opportunity

Bagnasco says he is convinced that the market is there for grafted vegetables, but the problem may be availability — at least in the short run.

“You don’t have to create a market yourself, look and see what is going on around the world,” he says. “A billion grafted plants were grafted in 2011. It is something that is catching on here.”

Doyle says retailers need to educate consumers on the advantages of grafted vegetables and why they should pay more (up to $8 a plant for the home gardener) than they would for plants grown from seed. When ordering liners, retailers should make sure they’re ordering vegetables that have been grafted to a desirable rootstock and that the plants are packaged properly.

The finishing of the plants can take place in any greenhouse with the desirable conditions for good growth. When transplanting to pots, keep the graft line as high as possible so that the gardener can easily keep it high. If the scion should root, the benefits of using a souped-up rootstock will be compromised, adds Doyle.

Other vegetables are being grafted, but they may not be as high-yielding as the grafted tomatoes. For instance, grafted peppers have about a 30 percent yield right now over seed-grown peppers, according to Bagnsco. Though this is a smaller increase of yield than tomatoes, he says a 30 percent increase in production is still significant for any grower, and it may improve as the technique is perfected.

 

Grafting Resources

Sources for grafted liners for tomatoes and other grafted plants:
www.plugconnection.com; Burpee Home Garden Bumper Crop, www.ballseed.com

Sources for wholesale grafted vegetable plants:
www.loghouseplants.com; www.harrisseeds.com; see www.mightymato.com for retail locations and contact Plug Connection for local wholesalers

Sources for individual grafted plants to trial:
www.gardenlife.com; www.territorialseed.com; www.jungseed.com

Sources for rootstock seed and clips:
www.johnnyseeds.com; www.territorialseed.com; www.awhaley.com

For information on grafting tomatoes and other plants, visit http://cals.arizona.edu/grafting/home



Neil Moran is a horticulturist and regular contributor to Produce Grower. Visit his website at www.neilmoran.com.


All photos courtesy Log House Plants (www.loghouseplants.com)

June 2013
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