Saturday, April 20, 2013

Tomato Grafting: My First Experiment by Duane Davidson

One of My Grafted Plants
In June, 2012,  Barb Klett wrote here on the subject of grafting tomato plants in an article "Grafted Tomatoes -- REALLY?" This is a follow-up, reporting my own experiences trying out this technique.

Early this year I was startled to see a familiar seedhouse catalog offering grafted tomato plants. I start a few tomato plants from seed each year, hoping to enjoy home-grown tomatoes mid- to late summer. But I had never heard of grafting tomato plants. I researched the subject and found the procedure intriguing.

We know that tomato plants, particularly the tasty old-fashioned varieties, are susceptible to a number of diseases that limit tomato fruit production and often kill the plant, once it is infected. We are taught to not grow tomatoes in the same spot each year and to remove and destroy any plant showing symptoms of disease before it spreads to other plants. I have not experienced any serious disease outbreak, but often have had a plant or two show leaf wilt in mid-summer or bear undersize fruit or fruit streaked with yellow.

The idea with grafting is to grow two kinds of tomato seedlings. One is a variety known to be disease-resistant (and maybe also to have shown particularly vigorous growth) but not known for bearing desirable tasty fruit. The other bears great fruit, maybe an "heirloom" such as Brandywine or Cherokee Purple. The first provides the root and a stub of stem; the other provides most of the above-ground plant and bears the fruit of choice.

I decided to try my hand at grafting the two together. I found another of my familiar seedhouses offering seed for two rootstock varieties and small plastic clips used to hold the two plant stems together. The clips were offered in several sizes. The catalog said the preferred sizes were for stems 1.5 mm and 2 mm in diameter (in packages of 200!). I ordered the 1.5 mm clips.

In my research I found a number of information sources, all land-grant universities, which I will list below. The seedhouse also sent multi-paged instructions on the grafting procedure. One of their points was that the stems of both plants, top and bottom, need to be the same diameter. I found this to be a stumbling point, as different varieties of tomatoes are apt to germinate and grow at different rates. The vigorous rootstock seedlings likely grow a little faster than the fancy fruit types. One source suggested a series of plantings, each a day apart, so that the tops and bottoms could be matched. This didn't seem to be feasible for my small-scale experiment with only a dozen each of tops and bottoms. And, as might be expected, some seeds germinated before others. Plus, by the time I had two matching stems, they had outgrown the 1.5 mm clips. I should have ordered the 2 mm -- or even some larger expandable clips that cost three times as much.

I didn't want to give up at this point and eventually I managed to graft two plants with nearly matching tops and bottoms that fit into the 1.5 mm clips on hand. The actual grafting was not difficult. I made cuts with a razor blade at a 45-degree angle on both plants, attached the clip to the bottom stem, and inserted the top stem into the top of the clip. The plants went into a "healing chamber" -- a plastic plant tray with a tall cover -- for three days of maximum humidity and low artificial light. They then were gradually reintroduced to normal humidity and light. (I start my plants under flourescent lights in the basement.)

Despite the less-than-perfect stem matching, and a little squeezing into the clips, the seedlings survived and began to grow. They went into the ground outdoors along with my conventional tomato seedlings -- and three grafted plants from the first seedhouse cited above. (Even if my grafted plants didn't succeed, I wanted to see how the very pricey professionally-grafted plants would do.)

Plant Has Shed its Graft Clip
Clip Has Begun to Slip off Stem
The results of my experiment were disappointing -- in a season of disappointing tomato production. I've found a couple of gardener colleagues who reported a good tomato crop, but most I've spoken with felt their tomato plants suffered in our extremely hot summer. Both of my home grafted plants were the variety Black Krim, which I've grown for a number of years, on the rootstock variety Maxifort. After about a month in the ground one of my plants withered and I removed it. I suspect it suffered both from the heat and from a less than perfect stem match in the graft, on which grew a noticeably large callus. The latter may have restricted movement of water and nutrients from the roots to the rest of the plant.

The remaining grafted plant produced several fruit, but not an abundant quantity -- and no more than a couple of my un-grafted Black Krim had borne. In contrast, the three professionally-grafted tomato plants produced well on vigorous vines that did well up to our first frost.
Closeup of Seed Company Graft
Grafted Plant from Seed Company

Conclusions to apply next year: 1. Grow more plants, both rootstock and several varieties of above-ground plants. Figure out a way to stagger seeding over several days, in order to maximize my choices on grafting day. 2. Buy larger clips, maybe even digging deeper in my pocket for the expandable type.

I realize this technique for avoiding disease and maximizing tomato production was developed to benefit large commercial growers, mostly in other parts of the U.S., and primarily in hydroponic operations. For the backyard gardener loss of a few plants usually is not a serious matter. I'm not suggesting that others need to graft their plants. For me it was an experiment, a challenge, and a learning experience. I didn't quite succeed this year, but am determined to do better next time.

Techniques for grafting other plants, including eggplant and cucurbits (cucumbers, melons) have also been developed.

Following are some sources for information on grafting tomatoes and other garden plants.

Ohio State University offers a wealth of information, including on-line videos:
North Carolina State University has compiled a list of plant grafting information sources:
Arizona State University's information resources on vegetable grafting include a 20-minute video available for $10 plus shipping: