Growing tomatoes in a greenhouse provides an ideal environment for maximizing their growth potential, but this rapid vertical development requires proactive support. Without a sturdy structure to climb, heavy stems and developing fruit clusters will quickly collapse, leading to broken branches and contact with the soil. Supporting tomato plants vertically is a foundational practice in greenhouse cultivation. This training prevents physical damage, limits the spread of soil-borne diseases, and ensures the plant’s energy is directed toward fruit production rather than sprawling growth. Vertical training also allows for higher plant density, increased air circulation, and a significantly larger yield within the confined space.
Essential Materials and Timing
Gathering the correct equipment is necessary for the long-term success of the crop. The primary structural components include a sturdy overhead support system, such as galvanized wire or metal conduit, secured across the greenhouse at the eaves or ridge. From this overhead line, a durable, untreated twine or cord, often made of polypropylene, will hang down to each plant. This twine must be strong enough to bear the full weight of a mature, fruit-laden vine, which can be considerable.
The support process must be initiated relatively early in the plant’s life to prevent the stem from bending or breaking. This intervention should happen when the tomato seedlings reach a height of approximately 12 to 18 inches, or just before the first flower truss begins to set fruit. Specialized plastic tomato clips or soft plant ties are also important materials, as they are used to secure the main stem to the twine without causing injury. Having all materials ready ensures the transition to vertical growth is seamless and not delayed, which can stress the young plants.
Vertical Stringing (Cordon) Method
The vertical stringing, or cordon, method is the preferred technique for greenhouse-grown indeterminate tomato varieties, which possess a continuous growth habit. This method begins by securely anchoring one end of the hanging string near the base of the plant, without harming the main stem or root system. A common practice is to bury the end of the twine loosely in the soil or growing medium, or to loop it gently around the base of the stem to form a non-constricting knot. The main stem must have enough room to expand in girth as it matures.
The opposite end of the string is then secured to the overhead support wire running horizontally across the greenhouse structure. As the plant grows taller, the main stem is trained to ascend the string using one of two primary techniques. The first involves gently twisting the main stem clockwise around the string, ensuring the twine is tucked securely into the crook of the leaf stems. This twisting should be performed once or twice a week to keep pace with the plant’s rapid vertical development.
Alternatively, specialized tomato clips can be used. These clips are attached to the string and then clipped around the main stem at regular intervals, typically every 6 to 12 inches. These clips provide a quick, firm attachment that allows for easy repositioning if needed. It is important to place the clip directly below a leaf or a fruit cluster, which provides a natural anchor point and prevents the stem from slipping down the string. Continuous vertical support is maintained by either twisting or clipping the plant until it reaches the overhead wire.
Ongoing Plant Management and Pruning
Once the indeterminate tomato plant is established on the vertical string, consistent maintenance and pruning are necessary to maintain the single-stem cordon structure. The most frequent task is the removal of “suckers,” which are small, vegetative side shoots that emerge from the axil, the point where a leaf stem meets the main stem. These suckers should be pinched or cut off when they are small, ideally less than two inches long, to focus the plant’s energy on the main leader and developing fruit clusters.
Allowing suckers to grow diverts carbohydrates away from the fruit and creates dense, bushy growth that reduces air circulation, increasing the risk of fungal diseases. For indeterminate varieties, this single-stem training is maintained throughout the growing season, promoting a high yield of larger fruit on a single vine. Determinate varieties, which stop growing at a set height, are generally not pruned this way and are better suited for different support methods.
Lowering and Leaning
As the main stem reaches the overhead wire, a technique called “lowering and leaning” is often employed to manage the plant’s height and maximize the long growing season. This involves carefully releasing the top portion of the string and gently laying the bare lower section of the stem horizontally along the ground or a low support. This action allows the growing tip to continue its upward trajectory, effectively utilizing the entire height of the greenhouse over time.
Leaf Removal
Regular removal of the oldest, lowest leaves is also a standard practice for ongoing management. Once the fruit on the lower trusses has been harvested, or when the leaves begin to yellow, they should be removed to a height just below the lowest developing fruit cluster. This selective leaf removal improves light penetration to the fruit, enhances airflow around the base of the plant, and reduces the incidence of soil-borne pathogens splashing onto the foliage.