Determinate tomato varieties, often called “bush” tomatoes, are genetically programmed to grow to a fixed, compact height, typically between three and four feet. They produce the majority of their harvest within a short, concentrated timeframe, setting them apart from vining cousins. While their growth habit suggests they might be self-supporting, the concentrated fruit load they bear often makes some form of structure a necessity for a successful harvest.
Defining Determinate Tomato Growth
Determinate tomatoes possess a distinct genetic trait governed by the SELF-PRUNING (SP) gene, which dictates their limited size and bushy shape. This programming causes the main stem and side branches to terminate in a flower bud rather than a vegetative shoot, effectively halting upward growth. This results in a compact plant structure that is shorter and denser than indeterminate varieties, which continue to grow until frost.
Instead of producing fruit continuously, determinate plants set and ripen a significant portion of their fruit simultaneously, usually over a period of one to two months. This simultaneous ripening means the entire plant carries a heavy, concentrated weight all at once. This characteristic makes them popular for those who want to process tomatoes for canning or sauce-making in a single batch.
Why Support Is Still Necessary
Despite their bushy growth and relatively sturdy stems, determinate tomatoes benefit significantly from support, especially when heavily laden with fruit. The concentrated weight of a large, simultaneous fruit set can easily cause branches to snap or the entire plant to topple over. Even a robust stem may struggle to support a heavy crop without leaning or sprawling.
Keeping the plant upright is also a preventative measure against common plant diseases. When foliage and fruit rest on the soil, they remain damp, creating an ideal environment for fungal diseases like early blight. Elevating the plant improves air circulation, allowing moisture to evaporate more quickly. This reduction in humidity helps manage disease pressure and promotes overall plant health.
Choosing the Best Support Structure
The ideal support structure for determinate plants accounts for their shorter, bushier form and concentrated weight. For these compact varieties, a well-placed stake or a sturdy cage is the most suitable option.
Staking
Staking involves driving a single, strong post (such as wood or rebar) into the ground near the main stem and tying the plant to it as it grows. This method helps the main stem remain vertical, which is effective for varieties with a strong central leader.
Caging
Cages are popular because they support the numerous side branches typical of bush-type growth. However, the flimsy, cone-shaped wire cages often sold at garden centers are inadequate for the heavy load of a full-sized determinate plant. A more robust option, such as a sturdy wire mesh cage or a homemade wood structure, is needed to handle the concentrated weight. The support structure should be installed when the plant is small to avoid damaging the roots.
What Happens Without Proper Support
Neglecting to provide support often leads to negative outcomes that impact the quality and quantity of the harvest. The most immediate problem is the plant sprawling across the soil once the fruit weight becomes too great for the stem and branches to bear. When fruit touches the ground, it is at a higher risk of developing rot and mold due to prolonged contact with moist soil.
A sprawling plant also makes ripening fruit easily accessible to ground-dwelling pests and insects, leading to increased crop loss. Furthermore, the stem and fruit-laden branches become vulnerable to breakage from the weight of the fruit itself or from wind. Harvesting from a collapsed plant is also significantly more difficult and time-consuming.