Major Factors in Preparing Grafted Vegetable Plants Successfully

Using grafted plants can benefit tomato and melon growers significantly. It is also clear that grafted vegetable plants can be prepared on farm and by hand in small-medium quantities. To obtain the benefits of grafted plants, they must be prepared properly. This Extension Spotlight outlines major steps in hand grafting. Other resources on the topic are available here. The availability of grafted tomato, melon, cucumber and other crop plants for purchase will increase with time as automated and semi-automated approaches improve.

Grafting is organ transplantation. As such, steps must be taken to ensure that the union of the rootstock (with its specialized root system) and scion (which produces marketable fruit) is complete and effective in every way for the grower.

First, the rootstock (RS) and scion (S) must be genetically compatible. New rootstock and scion varieties are available each year. Most commercial rootstocks should be compatible with most commercial fruit-producing (scion) varieties. That said, new RS-S combinations should be tested on a small-scale before being attempted on larger scales. The success of an attempted graft is usually evident in 7-10 days. Also, research-based information and experience from growers and others in the industry will help steer rootstock and scion selection.

Rootstock selection is usually driven by growers aiming to overcome specific challenges including soilborne disease, low soil moisture or fertility stress, salt stress, and/or temperature stress. Like scion varieties, rootstock varieties have been bred to have specific characteristics. Individual RS varieties may be effective at countering one or more of these problems but it is best to review RS options carefully. The root systems of nearly all RS varieties are more vigorous than the root systems of standard scions; therefore, grafting may improve crop performance even when growing conditions are generally good.

Second, the stem diameters of the rootstock and scion seedlings must be similar and correct. Stem diameters being similar is critical for two reasons. Similar stem diameters are easier to align during grafting. And, more important, similar stem diameters allow the grafted plant’s vasculature (xylem, phloem) and cambium (growing ring) to stitch properly, assuring strong, unrestricted movement of all substances form roots to shoots and vice versa throughout the life of the grafted plant. Stem diameters being correct is important because seedlings can be too small or too large to graft. In our experience, tomato seedlings should have a stem diameter of approximately 3mm (a little more than 0.1 inch) at grafting.

Finally, newly grafted plants must be allowed to heal in carefully controlled conditions. The actual graft (surgery) may require less than one minute but the healing period may last up to three weeks. During that time, temperatures around the grafted plant should remain 77- 86°F (for tomato), the relative humidity should remain around 95% and the light level should not exceed more than 75% of normal sunlight (approximately 50% for the first week after grafting is best). Grafters often achieve these conditions with the use of simple open-framed structures covered with plastic and shade cloth. We have also found that a flooded capillary mat beneath grafted plants gives them both the little water they need and adds humidity to the air in the healing chamber. The VPSL attempts to prevent liquid water from ever coming in contact with grafted plants while they are in the healing chamber – therefore, we use no hoses or large droplet vaporizers.