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Tales from a Plant Addict

Fun (& a few serious) facts, tips and tricks for every gardener, new and old.

Grafted Tomatoes


The first time I saw grafted tomatoes offered for sale, I thought it was a misprint. I'd heard of grafted fruit trees or grape vines, but vegetable plants? It fact it wasn't a mistake. There is such a thing as a grafted tomato. Commercial producers have used grafted plants for years with crops like tomato, eggplant, pepper, cucumber and melons. Grafting is still a relatively new phenomenon for home gardeners. But why go to the trouble of grafting a plant that only lives for one season?

There are two big reasons that tomatoes and other vegetable plants are grafted. One is prevention of soil borne disease. By using rootstocks resistant to common bacterial, fungal, viral and nematode diseases, the above ground portion of the plant is unaffected.

This can be a huge benefit to commercial producers and homeowners as well. By using disease resistant rootstocks, home and commercial growers can reduce or completely avoid pesticide use in an effort to prevent or eradicate disease.

The other recognized benefit of growing grafted tomato and other vegetable plants is increased yields. Researchers have demonstrated this yield increase in situations where soil borne disease is a problem, but also where these diseases are not present. Yields up to four times that of the same non-grafted variety of tomato have been reported.

Researchers hypothesize that the disease resistant rootstocks used on the grafted plants can more efficiently transport food and water to the above ground portions of the plant, resulting in increased yields. They have also demonstrated that the root systems on grafted plants are much more extensive than their non-grafted counterparts, making it easier for the plant to access water and nutrients in times of environmental stress.

It's also important to note that these increased yields are not typically seen in container grown plants. This is probably related to restricted root growth when growing tomatoes in a container.

Grafted tomato plants are commercially available locally, but expect to pay about $10 to $15 per plant, compared to a non-grafted plant that costs under $5. The concept of grafting a tomato plant is deceptively simple– take the above ground portion of the tomato variety you wish to harvest, and the root portion of a disease resistant variety, match the cut stems, let them grow together and–voilĂ -- a grafted tomato plant. Unfortunately if it were that simple the plants would not retail for $10 and up.

Grafting tomatoes successfully hinges on matching the diameter of the cut stems of the scion (the above ground portion you wish to harvest fruits from) and the rootstock (the disease resistant root portion). It seems easy enough until you realize that not all tomato seedlings are created equal. Some varieties grow faster and are more vigorous than others.

Any tomato variety can be used as a scion, but rootstocks are usually a role reserved for varieties with known resistance to soil borne diseases. Some seed companies are developing varieties specifically for rootstock use. But many traditional hybrids have potential for use as disease resistant rootstocks. Variety names that are followed by a series of letters are resistant to specific diseases. For example, the variety 'Roma V F N AS' is bred to be resistant to Verticillium and Fusarium Wilts, Nematodes, and Alternaria Stem Canker. Seed companies are supposed to use one of two systems of abbreviations for noting disease resistance, but I have seen some pretty wide variations in print. You may need to call the seed company or search online to decipher the codes.

When grafting tomatoes, plan on starting the process at least two weeks before non-grafted tomatoes would typically be planted. This allows time for the graft to heal. It would also be a good idea to plant a few of the rootstock and scion seeds long before you plan on grafting, just to check germination times and seedling size. When the time for grafting approaches, you will at least have an idea of when to start and stagger plantings of scion and rootstock seeds to achieve seedlings of equal size. If either scion or rootstock seedlings are growing too fast, try reducing the air temperature to slow their growth while the other variety catches up.

Grafting is typically done when tomato plants have two to four true leaves. The scion and rootstock stems are each severed at a 45 degree angle, and the scion stem is matched up with the rootstock stem. The diameters of the stems must be exactly the same diameter for the graft to be successful. A common method for grafting tomatoes is called tube grafting and uses tiny rubber or silicone clips to hold the cut stem ends of the two seedlings together for healing.

Following the grafting procedure, seedlings must be kept in a healing chamber, where the humidity is high and the plants are not exposed to direct sunlight. This can be as simple as a frame covered in opaque plastic placed over the grafted seedlings. Ideally in two to four days the two stems will grow together, forming a new grafted plant.

Some wilting is normal in the first day following grafting, and after two to four days, successfully grafted plants will no longer show any signs of wilting. For the following week, plants should be gradually reintroduced to light, whether natural or artificial, and lower humidity. It is normal for the grafting clips to fall off as the plants resume growth.

Plants should be monitored closely and gradually acclimated to outdoors just like any other tomato seedling. Take care to plant the seedling with the graft above the soil surface to prevent the scion stem from rooting. Allowing the scion to root would defeat the purpose of grafting a disease resistant rootstock onto the scion.

Grafting is a numbers game. Expect many more failures than successes, especially in the beginning. Plan on grafting way more plants than you actually need. Increase your odds of success by keeping your growing and grafting areas as clean as possible. Use fresh, sterilized potting media. Wash your hands with anti-bacterial soap and use latex gloves and sterile tools when doing the actual graft. Water newly grafted plants from below to avoid dislodging the healing grafts.

I will try my luck at grafting tomatoes this winter, and hopefully will be able to grow some grafted plants next summer. In the meantime, it is time for the 8th Annual Tomato Taste Panel on Thursday, September 12th at the U of I Extension office in Macon County. We have planted over 40 different tomato varieties to taste this year. Tasting sessions will be at 1 pm and 6 pm. Please register by calling (217) 877-6042.



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I am experimenting with grafting some tomatoes this year and after one week they look OK in the humid environment (95%) but start wilting almost immediately if the cover is even partially removed. How are yours doing?
by Elaine Vidal on Sunday 4/27/2014