Supporting tomatoes grown in fabric containers, or grow bags, is necessary to prevent stem breakage, improve air circulation to deter disease, and maximize the harvest. The soft walls and loose medium of a grow bag do not provide the structural anchoring of dense garden soil, creating unique challenges for supporting a tall, fruit-laden plant. Successful support requires selecting the correct structure for the tomato variety and ensuring that structure is firmly stabilized against tipping.
Matching Support to Tomato Growth Habit
Tomato varieties are categorized by their growth habit into two main types, which determines the necessary support system. Determinate varieties, often called “bush” tomatoes, grow to a predetermined height (usually two to five feet) before setting fruit all at once and stopping growth. These plants are well-suited for smaller grow bags (five- to ten-gallon range) and require less intensive support due to their compact structure.
Indeterminate varieties grow like vines, continuously producing new foliage, flowers, and fruit until frost. These vining plants can easily reach six to ten feet tall and require a larger container, typically 15 to 20 gallons, along with robust vertical support. Their perpetual growth means the structure must be substantially taller and stronger to handle the increasing weight throughout the growing season.
Low-Profile Support Methods
For compact determinate varieties or tomatoes in smaller grow bags, low-profile support methods are generally sufficient and contained entirely within the bag itself. The most common choice is a short tomato cage, effective for varieties that do not exceed four or five feet in height. When selecting a cage, choose one with a diameter that fits within the grow bag’s circumference but is large enough to contain the bushy growth.
Alternatively, a single stake (made of wood, metal, or bamboo) can be used for shorter plants. It is important to insert any support structure immediately upon transplanting the seedling to avoid damaging the developing root system. Pushing a stake into the bag later risks severing feeder roots, which can stunt the plant’s growth and reduce yield. For added stability, consider using heavy-duty, wider cages, or stacking two standard cages (one placed upside down on top of the other) in a ten-gallon bag.
Stabilizing Tall and Heavy Supports
The primary challenge of growing indeterminate tomatoes in grow bags is that the loose potting mix cannot anchor a six- to eight-foot stake or trellis against the leverage of a heavy, wind-catching vine. A tall, single stake will inevitably become wobbly and tip over once the plant is laden with fruit, especially in windy conditions. To counteract this lack of soil depth and weight, the support must be anchored externally to the grow bag.
One effective solution is creating a tripod or teepee system using three stakes lashed together at the top. The stakes are driven into the soil medium near the edge of the grow bag, distributing the plant’s weight and creating a self-supporting, stable base. For greater security, you can tie the top of the structure to a fixed external element, such as a deck railing, fence post, or house wall, using a strong rope or wire. External weights, like heavy bricks or paving stones, can also be placed around the base of the grow bag to secure the feet of the support structure and prevent the entire container from toppling over.
Proper Tying and Training
Beyond the initial setup, ongoing maintenance through proper tying and training is necessary to manage the vertical growth of the tomato plant. As the plant grows, the main stem should be secured to the support structure every ten to twelve inches. The material used for tying must be soft and flexible to prevent it from cutting into the tender stem as the plant thickens.
Soft materials are ideal for this task:
- Stretchy fabric strips
- Old nylon hosiery
- Wide Velcro garden tape
- Heavy-duty cotton or nylon twine
When tying, form a loose loop in a figure-eight pattern, with one loop around the stake and the other around the stem, ensuring enough slack for the stem to expand without being constricted. Indeterminate varieties also benefit from the removal of “suckers,” the small side shoots that form in the crotch between the main stem and a leaf branch. Removing these suckers (pruning) reduces foliage mass and redirects the plant’s energy toward fruit production on the main vine, lessening the total weight the support system must bear.