​How To Combine Two Desirable Traits


Grafted tomatoes in the UT Gardens, Knoxville

In 2016 grafted tomatoes were grown in the University of Tennessee Gardens, Knoxville, and at several other locations across the state to provide Tennessee gardeners with useful information about using the technique in their home gardens. Photo by N. Bumgarner, courtesy UTIA. Download image.

Click here to see an image of a graft seam on a tomato plant.


From the UT Gardens
September 2016 Plant of the Month: Grafted Tomatoes

Submitted by Natalie Bumgarner, Assistant Professor of Residential and Consumer Horticulture and Tennessee Extension Master Gardener

Tomatoes are among the most widespread plants found in home gardens. It seems everyone grows tomatoes, and everyone has their favorites. A quick scan through a recent vegetable seed catalog is likely to present the gardener with a wide array of seeds and plants. Many are preferred because of their flavor, some because of their size and others because of their disease resistance. Wouldn’t it be nice to combine the most desirable traits?

Well, grafting may help us do just that. The basic idea behind grafting is to combine the best traits of two different cultivars into one garden plant. The technique is a well-known concept throughout the industry, but most home gardeners are more familiar with its use in fruit trees and ornamentals. Still, you can successfully graft tomatoes.

To graft a tomato, start by choosing a cultivar with a desirable fruit trait, like flavor. The top part of your graft (called the scion) will exhibit your preferred fruit traits. The bottom of the graft (called the rootstock) is specifically selected to have root characteristics that are most desirable. As an example of a possible benefit, some common heirloom tomatoes, which are considered better tasting by some gardeners, may not have resistance to some of the wilt diseases (Fusarium, Verticillium) or pests (nematodes) that can enter through roots and kill the plant or lower its yield. Another reason to choose a particular rootstock might be improved vigor, which would enable the plant to be more productive or have a longer season.

So, exactly how would you graft a tomato? Seeds of both the scion and rootstock are planted in a home or greenhouse. Then when the plants are still fairly young and a few weeks away from transplant size, they can be grafted. Techniques vary a bit in terms of specific cuts and types of grafts, but both plants are severed and then gently placed in close contact (secured by a clip) so their vascular systems can grow together. One of the most critical aspects is keeping the young plants in a location (called a healing chamber) where they have low light and high humidity for a few days to enable them to heal and produce one healthy transplant.

Grafting can certainly be done at home on a small scale; however, if the process sounds a bit complex to do yourself, many seed and plant sellers offer grafted and already healed tomato plants for sale.

At UT, we are carrying out several trials to help answer whether grafted tomatoes can be useful and desirable in your garden. This year, grafted tomatoes were grown in demonstrations and trials at the UT Gardens, Knoxville, and at several other sites across the state. With these and future efforts, we hope to provide Tennessee gardeners with information to help them decide whether grafted tomatoes could improve the success or productivity of their vegetable gardens. 

The UT Gardens includes plant collections located in Knoxville, Jackson and Crossville. Designated as the official botanical garden for the State of Tennessee, the collections are part of the UT Institute of Agriculture. The gardens’ mission is to foster appreciation, education and stewardship of plants through garden displays, educational programs and research trials. The gardens are open during all seasons and free to the public. For more information see the Gardens website.

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Contact:

Natalie Bumgarner, UT Department of Plant Science, nbumgarn@utk.edu

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For more information about desirable tomato rootstock cultivars and disease resistances, see this UT Extension Factsheet on Tomato Diseases.