Grafting is a horticultural technique that joins two separate plants, merging the desirable top portion (scion) of one plant with the root system (rootstock) of another. This method combines the genetic strengths of two distinct varieties into a single, high-performing plant. For the home gardener, this skill provides a practical way to cultivate flavorful, heirloom varieties while protecting them from common soil-borne issues. This guide details the preparation, execution, and specialized care required for successful tomato grafting.
Why Grafting Tomatoes is Beneficial
Grafting protects susceptible, high-value varieties from pathogens residing in the soil. The primary benefit comes from selecting a robust rootstock that is resistant to common diseases like Fusarium wilt, Verticillium wilt, and root-knot nematodes. This resistance prevents soil-borne pathogens from entering the plant’s vascular structure. This strategy is useful in gardens where crop rotation is limited or where soil has become fatigued.
The secondary benefit is increased plant vigor and productivity. Specialized rootstocks are bred for efficient water and nutrient uptake, resulting in a stronger, healthier plant above ground. This enhanced root system allows the plant to handle environmental stressors, such as temperature fluctuations or drought, more effectively. Grafted plants often produce higher yields, a longer harvest window, and larger fruit.
Selecting and Preparing Your Grafting Materials
Successful grafting requires two components: the scion and the rootstock. The scion is the top portion chosen for its desirable fruit characteristics, such as flavor or size. The rootstock is the bottom portion, selected for its vigorous growth and ability to resist specific soil-borne diseases. Commercial rootstock varieties known for their broad resistance profile include ‘Maxifort’ or ‘Beaufort’.
Timing is crucial, as the stem diameters of both the scion and rootstock must match closely for a successful union. Grafting is typically performed when seedlings are young, usually at the two-true leaf stage (about four to five weeks after seeding). All tools must be sterilized using rubbing alcohol to prevent disease transmission. Essential supplies include a sharp razor blade or scalpel, a clean work surface, and specialized silicone grafting clips.
Step-by-Step Guide to the Grafting Process
The most reliable technique for home gardeners is the splice graft, which involves making matching diagonal cuts on both stems. Begin by sterilizing your cutting tool with alcohol before the first cut and between every few plants to maintain a sterile environment. Next, select a healthy rootstock and remove the top portion of the plant at a point just above the cotyledons, making a precise 45-degree angle cut through the stem. This cut must be clean, without any crushing or tearing of the plant tissue.
Immediately following the rootstock cut, perform an identical 45-degree angle cut on the scion, removing its root system at a point where the stem diameter perfectly matches the rootstock. The stem diameter match is perhaps the most important factor, as the vascular cambium layers—the tissue responsible for growth—must align for the two parts to fuse successfully. The cut surfaces should not be allowed to dry out, so working quickly is beneficial to prevent desiccation.
The two newly cut pieces are then joined together and immediately secured using a silicone grafting clip. The clip gently holds the scion and rootstock in place, ensuring the cut surfaces are in full, gap-free contact. The goal is to align the outer edges of the stems to maximize the contact between the vascular rings, allowing the plant to form a callus bridge that reconnects the water and nutrient transport systems. After securing the union, the newly grafted plant must be moved immediately to a specialized environment to begin the healing process.
Post-Grafting Care and Acclimation
The immediate period following the graft is when the plant is most vulnerable and requires a controlled environment known as a healing chamber. This chamber, often a humidity dome or specialized tent, must maintain near-saturated humidity levels, ideally between 90 to 100 percent, to prevent the scion from wilting. High humidity is necessary because the scion has no functional root system to supply water until the graft heals, and moisture must be absorbed directly through the leaves.
Temperature within the chamber should be kept consistently warm, typically between 72°F and 85°F, as this range promotes rapid cell division and callus formation at the graft site. For the first one to two days, the plants need very low light or near darkness to minimize transpiration stress. After this initial period, the light is gradually increased, often by removing shade cloth or moving the plants to a slightly brighter area.
The process of acclimation, also called hardening off, takes approximately seven to ten days and involves slowly introducing the plant to normal growing conditions. Humidity is reduced gradually over several days by opening the chamber vents or lifting the dome, which forces the plant to rely on its newly formed vascular connection. Once the graft union appears fully healed and the plant shows no signs of wilting under ambient humidity, the silicone clip can be removed, and the plant is ready for transplanting. Care must be taken during planting to ensure the graft union remains well above the soil line, which prevents the scion from developing its own roots and negating the benefit of the resistant rootstock.