Grafted Tomato plants in your future?

The new 2013 seed catalogs have been arriving and I noticed, for the first time, that some catalogs are offering grafted tomato plants this year. Well, it turns out they have been available to home gardeners in the US for several years now, while they have been extensively used in Europe and Japan, and in US greenhouse agriculture, for years. The concept of grafting is a very old horticultural practice. Roses and fruit trees (members of the Rose family) are routinely grafted onto rootstock because they do not run true from seed. And of course, we all know the European wine industry was saved when an entomologist in Missouri developed a method of grafting Vitis vinifera scions onto phylloxera-resistant American root stock.

 

What is new to me is the concept of grafting non-woody annuals like tomatoes, cucumbers, peppers and eggplants. What advantage can be obtained? Grafted tomato plants in the catalogs are priced $8-10 each, so what would make that price worth the benefits? Japan was one of the early adopters of grafted plants, a country where space is at a premium. Then Europe. In the US, greenhouse growers are the economic driver behind grafted plants and the economics are simple. Greenhouses are a large capital investment and have a finite capacity for plants. If the productivity of a given plant could be improved for whatever reasons (vigorousness, soil disease resistance, etc.), say 40-50%, that would be a huge payback for the additional cost of grafted plants. Even for field-grown tomatoes, a significant yield per acre is money in the bank.

 

Do grafted plants have any benefits for the average home gardener? I think that remains to be seen, but the potential is intriguing. A number of benefits are claimed for grafted plants. Among them are increased vigor, extended harvest and disease resistance. Suppose you take a vigorous, disease tolerant rootstock and graft it with a desirable heirloom tomato such as Brandywine. If the grafted plant can produce even 50% more fruit for the one spot I can devote to a Brandywine plant, it would be worth it to me.

Here are some of the claimed benefits of grafting:

More vigorous rootstock that can pump more nutrients into the grafted scion. There are claims that the root mass of the rootstock may be 4-5 times larger than usual. The rootstock is capable of delivering far more nutrients to the scion, yielding more and larger fruit, thus increasing productivity. There is of course an art to pairing rootstock  to scion. Too much vigor and you may overwhelm the scion and  just get rampant vegetative growth. My concern comes from growing in raised beds, where I have constrained volume for each plant, both root mass and foliage. The growers recommend pruning to two leaders to spread the vigor, which was my practice for in-ground plants trained up a pole. In raised beds, I prune to a single leader trained up a trellis cord. At the end of this season I pulled tomato plants with large root systems that consumed their own square plus most of the adjacent square. Do I really want a plant with 4-5 times the root system?

Improved disease resistance, primarily from soil-borne diseases. The root stock varieties are selected for their resistance to some soil-borne diseases and nematodes. For example, Estamino, an organic rootstock bred by Enza Zaden in the Netherlands is grown by King Seeds in the US and retailed by Johnny’s and High Mowing Seeds. Estamino has strong resistance to Verticillium and Fusarium wilts, tomato mosaic virus and leaf mold. It has intermediate resistance to root knot nematodes and tomato spotted wilt virus. The airborne diseases like late and early blight aren’t mentioned, but I have seen blight resistant varieties like Defiant grafted onto rootstock, giving you the best of both. Unfortunately, Defiant is a determinate variety not suited to trellis training. Still, the soil disease resistance is a definite plus for situations like hoop houses, greenhouses and raised beds where there is limited to no opportunity to practice crop rotation. Graft an heirloom with no disease resistance onto rootstock and you get the disease resistance of an hybrid.

Extended production of fruit. The combination of disease resistance with a vigorous rootstock means that plants will keep growing and producing fruit. For a greenhouse with a controlled environment, that is an obvious advantage. If it proves true in the home garden, that would also be a plus. My tomatoes tend to tire out in late summer. This year they only got about 4 feet up a 6 foot trellis. I am no disease expert but I suspect diseases may play a role in this. Usually I am hoping the couple of fruits still on the vine will mature before cold weather. I think that instead, wondering what to do with the bushels of green tomatoes still on the vine would be a pleasant problem to have.

 

\If you want to see how grafting is done (and why retail grafted plants are expensive), there is a great video produced by the University of Vermont here. And just a WARNING: While grafting is not GMO, it is a high-tech process used in agribusiness and Monsanto is heavily involved. The Dutch company De  Ruiter, a Monsanto company, is the source of seed for the Maxifort, Multifort and Beaufort rootstock which are widely used. Seminis has its own rootstock, Cheong Gang. Johnny’s and others do offer rootstock seed not produced by Monsanto but retail growers don’t always volunteer what rootstock they are using. It looks like Log Cabin Plants sold by Territorial in 2011 used Emperador rootstock from Syngenta in the Netherlands, a non-Monsanto product. For 2013, they are using a rootstock branded “SuperNaturals” and it isn’t clear if this is Emperador re-branded or a new rootstock. If you are concerned about avoiding Monsanto products, you should probably ask what rootstock is used.

 

I am definitely intrigued by the concept of grafting tomatoes and will probably try a few plants in 2013. Right now I would have to mail order plants, since I haven’t seen grafted plants at any of the garden centers around here in New England (although Home Depot has trialed selling the Mighty ‘Mato grafted plants, but only online). In the US (outside of the greenhouse industry), most home garden activity seems to have started in the Pacific Northwest, with Log Cabin Plants and retailers like Territorial Seeds. Log Cabin in conjunction with Garden Life developed the Might ‘Mato brand and they seem to be the major grower/promoter for now. Retailers like Home Depot, Territorial, Jung, Totally Tomatoes (and allied Vermont Bean Seed), White Flower Farms, and others are reselling selected Mighty ‘Mato plants. The widest selection seems to be offered by Garden Life itself. Plants will also be available from some garden centers (primarily in western US but hopefully in the NE as well). Expect to pay an average of $8 per plant plus shipping (and usually a 3-plant minimum order). And you probably should order early if you are serious because production is limited.

 

So, do you have any plans to plant grafted tomatoes in 2013? Have you done so before/? I am thinking of trying a grafted Cherokee Purple, because I am such a fan of it and last year was disappointing. Garden Life also offer Paul Robeson, a Russian heirloom that is supposed to be great tasting and early. Then what about Juliet? It is already vigorous and productive, but if I could get 50-100% more fruit from one vine, I only need to plant one of them. I am not ready to try eggplant or pepper yet. I doubt an 8 US$ eggplant is going to be any less susceptible to flea beetle attacks than my 50 cent transplants.