Last year you may have seen larger, pricier tomato plants labelled as “Grafted", at your local greenhouse and in catalogs. If not, you will certainly come across them this year, as they are a hot trend. So, what's the scoop?
Grated tomato plants have the root system (root stock) of one variety melded to the top fruiting portion (scion) of another variety. Grafting has been used for thousands of years for fruit trees.
Grafting is used in the, often successful, attempt to have “the best of both worlds" - with regards to root health and fruit production. Roots stock is selected for such things as strong growth, disease resistance or cold tolerance. Scion may be selected for fruit qualities such as taste, size, appearance or storage life.
In the most popular of grafted tomatoes, scions from much-loved heirloom varieties are being joined to more vigorous and disease resistant rootstocks. This root vigour may give a more generous yield of tomatoes, thus making up for the extra up-front cost.
If you're familiar with the tomato growing trick of burying the stems extra deep, or on their sides, to promote extra root growth – forget about that! When you plant grafted tomatoes you must keep the graft union (the line on the stem where scion and rootstock meet) above the soil. They already have a beefed up root system; if you bury the graft union the scion will sprout roots, defeating the purpose of growing grafted tomatoes.