Wednesday, January 19, 2011

Using Grafting in Organic Heirloom Tomato Production

This is day 2 of a series of 5 blogs from the Great Plains Growers Conference that took place at the beginning of January 2011.  This series of blogs is from the Organic Track.

Using Grafting in Organic Heirloom Tomato Production presented by Cary Rivard, Plant Pathologist, North Carolina State University

Prior to making the decision to graft heirloom tomatoes, one must consider their market. Grafted plants cost approximately $1-$2 more per plant to produce than producing traditional plants. Thus, growers should only consider grafting heirloom tomatoes if they can get a market premium price for heirloom tomatoes.

Many heirloom tomato varieties have a well deserved reputation for being “finicky” and less than vigorous. However, heirlooms produce some of the tastiest and most marketable tomatoes. When grafting, one can select a scion variety based on fruit production, and select a root stalk based on vigor and hardiness. The results of this selection process are the true benefits of grafting heirloom tomatoes: disease resistance, water & nutrient uptake, and increased yields. An heirloom tomato plant may theoretically produce the most beautiful and marketable tomatoes, but that doesn’t matter one bit if an entire crop is wiped out by fusarium wilt. Root stalks can be selected with resistance to the specific diseases and pests that commonly infect the scion variety. The same principle holds true for water and nutrient uptake. Hearty tomato plants are so vigorous in part because they can take in water and nutrients more efficiently than other plants. Root stalk should also be selected based on these uptake efficiencies. Lastly, test trials indicate that grafted plants can produce higher yields than traditional heirloom plants, even when the traditional heirloom plant was fumigated and the grafted plant was not.

Dr. Rivard presented an overview of the process of grafting. A short run through of those steps follow, but I recommend acquiring more detailed information from his research and resources pages at the North Carolina State University website.

The entire process should be treated as surgery; sanitation is essential in every step of the process. Once appropriate scion and root stalk have been selected the grower will need to raise the plants until they are approximately 3-week old seedlings (1.5-2.0 mm stem diameter). The stem diameter of the scion and the root stalk must be the same. Unlike with most seedling propagation, a long stem is preferable for grafting. When the plants are ready, the space and materials must be sanitized and prepared for the process. Dr. Rivard suggests grafting at night (so the plants aren’t water or nutrient stressed). The cuts should be made at an angle between 45˚ to 60˚. Consistency of angle is more important than the actual degree of the angle, as the stems will need to connect like puzzle pieces. Once the cuts are made, attach a tube clip to the root stalk and insert the scion, making sure to line up the angles of the cut ends. The grafted plants should be placed in a healing chamber as soon as possible. The most important qualities of a healing chamber are that it has high humidity and very low light. Once the graft sites have healed, the plants can be hardened off and transplanted into the ground (shallow transplanting is important, to avoid volunteer roots and root suckers).
(reported by Rachel Deffenbaugh – Gateway Greening, Inc., St. Louis, MO)

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