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Graft is Good
by Carol Michel - posted 10/16/13


Grafted tomatoes will produce a stronger root system and a larger plant overall.

Are you disappointed in the number of tomatoes you are harvesting from your heirloom variety tomato plants? Heirloom tomatoes, like ‘Brandywine’, ‘Mortgage Lifter’ and ‘Black Krim’, are some of the best-tasting tomatoes to grow, but often the number of tomatoes you get from an heirloom tomato plant doesn’t seem to be worth the effort. This is because many heirloom tomato plants are less vigorous and more prone to disease than hybrid tomatoes.

Hybrid tomatoes, on the other hand, are often bred to be disease resistant and to produce more fruit, but they may not taste quite as good as heirloom tomatoes.

We seem to be stuck with two choices. Should we grow a better-tasting tomato, but get fewer tomatoes overall from each plant? Or should we grow a tomato variety that produces more tomatoes per plant, but isn’t as flavorful?

How about a third choice? How about growing an heirloom variety that has a better taste on a plant that is more vigorous and disease resistant? With the introduction of grafted tomatoes for home gardeners, this third choice is now an option.

History

While grafted tomatoes seem like a new trend in the United States, growers have been grafting tomatoes and other vegetable plants, including watermelon and eggplant, for decades. According to researchers at Washington State University, there is mention of self-grafted watermelon plants in China as far back as the 5th century, but it was not until the early 20th century that growers in Japan experimented with grafting watermelon plants onto squash rootstocks to increase the vigor of the watermelon vines. Today most of the commercial growers of tomatoes in Asia, Canada and Mexico use grafted tomato plants.

Why Graft Plants?

The reasons for grafting plants are the same whether it is a fruit tree, a rose or a vegetable. A plant bred for better fruit or flowers may not be a strong, disease-resistant plant. Grafting that plant onto the rootstock of another plant that is a strong, disease-resistant variety will result in a plant with the best qualities of both — disease resistance and better fruit or flowers.

There are several techniques for grafting, but all involve the same basic principle. A scion, the upper portion of a plant that was selected for superior fruit, is cut from its roots and grafted onto a rootstock that was selected for its vigor and disease resistance.


Grafted tomatoes produce more tomatoes on stronger plants. On the left is a grafted tomato growing next to the same variety grown from seed.

After grafting, the seedling needs to be kept in a healing chamber for at least a week until the graft heals and the rootstock can support the scion.

For tomatoes, the rootstock is generally from a nearly wild tomato, according to Scott Mozingo, product manager for Burpee Home Gardens, who has been trialing grafted tomatoes for several years. Mozingo noted that what is needed for a successful tomato graft is to have a scion and rootstock that are the same diameter. Once the plants are joined together, and held together using a variety of techniques, they are placed in a healing chamber. The healing chamber is a sterile, low-light, high-humidity, temperature-controlled environment that helps to keep the scion alive until the graft with the rootstock takes hold and the scion can begin to receive water through the rootstock.

Growing Grafted Tomatoes


Tomato plants should be planted so the graft union is at least 1 inch above ground.

When grown in the home garden, the grafted tomato will have better roots than other heirloom tomatoes, so they will require more fertilizer and water through the growing season. The general rule of thumb for most vegetable gardens is to ensure the garden gets at least 1 inch of water a week, from either rain or supplemental watering. Fertilize the tomato plants regularly, especially once they begin to bloom.

The grafted tomato plant will have more growth than an heirloom tomato plant grown from seed, so provide strong support for the vines. Depending on your preference, the tomato plants can either be staked or caged. Suckering, the removal of shoots that appear between the leaf axils and the main stem, is also a matter of preference. Because of the size of the grafted tomato plants and the more extensive root system, they will not grow well in containers.

Grafted tomatoes should be planted so that the graft union is about 1 inch above the soil line. As the tomato grows, watch for suckers or side shoots that come up from the base of the plant and remove these, whether they come from above or below the graft union. These side shoots use up water and nutrients and can result in a less vigorous main plant.

Are They Worth the Higher Price?

Because there is labor involved in grafting, grafted tomato plants will cost more than the same variety of tomato grown from seed. Are they worth the extra cost? Grafted tomatoes have improved disease resistance, so in areas where fusarium wilt or verticillium wilt are a problem, they are a good alternative. Grafted tomato plants have also been shown to produce more fruit when grown side by side with seed-grown plants, which may also offset the higher cost.

According to Burpee Home Gardens’ Mozingo, grafted tomatoes grown in the Midwest have also shown more environmental tolerance, growing better in drier, hotter summers than seed-grown tomatoes. The stronger roots of the grafted tomatoes run deeper and farther, which provides the plants with more water. In addition, the grafted tomatoes often produced fruit five to 10 days earlier than the same variety grown from seed.

Is it possible for gardeners to graft their own tomatoes to save money? The answer is “probably not.” Though techniques for grafting tomatoes and other vegetables have been refined over many decades so they can be mass produced, the average gardener would need to find a source for the rootstock and time the growth of the rootstock seedlings with that of the scion seedlings so they are the same diameter when grafted. A gardener would also have to build a healing chamber to control the temperature, humidity and light while the graft heals.

Buying grafted tomatoes is like buying an insurance policy, notes Mozingo. They may be your best hope for enjoying more heirloom tomatoes, regardless of the soil-borne diseases or weather extremes that may afflict your garden.

From State-by-State Gardening July/August 2013. Photos Courtesy of Burpee Home Gardens.

 


Carol Michel is a freelance writer with a degree in horticulture from Purdue University. She blogs about gardening regularly at maydreamsgardens.com.