Garden View
July 2007

Tomato Habits (Why We Do the Things We Do)
by Robert Blade

Gardeners have numerous methods of training tomatoes in the garden and in the greenhouse. I use the Barnum and Bailey method. It involves holding a chair between the unruly tomato plant and myself, and cracking a whip. I don't have much luck growing a crop, but I certainly enjoy the experience. Why do we prune and train the delicious nightshade in the first place? (Please notice the use of the word "why" to ask a question.) Pruning is a management tool that is used to reduce the number of branches a plant produces in order to increase fruit size, and to direct plant growth as part of training. Training is directing plant growth vertically in order to maximize the use of growing space, improve air circulation for disease control, increase leaf surface exposure to light, prevent fruit contact with soil, and to make harvesting easier.

The truly serious gardener should understand that the pruning and training of tomatoes varies depending upon the plant's growth habit. Neither a good habit nor a bad habit, a tomato demonstrates indeterminate, determinate, or semi-determinate growth.

Indeterminate types (beefsteaks, Stupice, Taxi, Brandywine) are typically the traditional, large, home garden tomatoes and most heirloom varieties. They will continue to grow and produce fruit as long as the season lasts. The branches are widely spaced and produce numerous suckers, or side shoots from the crotch formed between the branch and the main stem. Determinate tomatoes (Oregon Spring, Window Box Roma, Burbank Slicing) have shorter branches that are spaced closer together, producing a bushier and more compact plant. The number of stems, leaves, and flowers produced are predetermined by the plant's genetic make-up. Once a determinate tomato plant has reached a certain size, it ceases vegetative growth (leaves and stems) and expends all its resources in the ripening of its fruit. Most of the fruit ripens at the same time providing a single early harvest. Semi-determinates (Celebrity) fall in the middle of these other two categories. Seems a bit wishy-washy to me.

Most gardeners use tall stakes (4'-6'), fence or trellis, or strings hanging from an overhead support to train indeterminate tomatoes. Short stakes (2'-4'), cages or hoops work best with the shorter, bushier determinate varieties.

Determinate tomatoes don't benefit from much pruning (if any) due to their limited growth and number of fruit produced. Indeterminate tomatoes benefit from pruning the side shoots, but do not require their removal. A tomato cultivar trial and pruning observation performed by Iowa State University in 2000 concluded that pruning increased fruit size by 25%, but reduced the number of fruit harvested by 32% and the total marketable weight by 15%. Fruit rot and ground spotting as a result of tomatoes in contact with the soil were not a factor in the study due to dry conditions and the use of black plastic mulch.

The general consensus is, however, that indeterminate tomatoes are more manageable when pruned and trained upright. Horizontal stems tend to branch more frequently, creating the potential for an impenetrable tomato jungle. Prostrate plants begin fruit production later (2-3 weeks) and the fruit tend to be smaller and ripen at the same time. Tomato plants pruned and trained to a single stem (2-3 at most) have almost every leaf receiving sunshine and producing sugar which is directed to the developing fruit rather than developing new branches.

There's nothing like resting under the shade of the tomato tree on a hot summer day, enjoying the taste of a freshly picked tomato. Really.

Rob Blade lives in Rice, Washington. He designs and installs gardens. For more information, call 509-738-2964 and ask for a brochure.

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