Yard and Garden: Grow Tomatoes

Tomato plants are the most popular vegetable in the home garden. Iowa State University Extension garden specialists explain varieties, growth habits and how and when to plant this vegetable of many sizes, shapes and colors. Gardeners with additional questions can contact the experts by calling or emailing the ISU Extension horticulture hotline at 515-294-3108 or hortline@iastate.edu.

In regards to tomatoes, what is meant by the terms “determinate” and “indeterminate”? 

Determinate and indeterminate describe a tomato variety’s growth habit. Determinate tomatoes are small, compact plants. They grow to a certain height, stop, then flower and set all their fruit within a short period of time. The harvest period for determinate tomatoes is rather short, making them good choices for canning. Indeterminate tomatoes continue to grow, flower and set fruit until killed by the first frost in the fall. Accordingly, the harvest from indeterminate varieties often extends over a two to three month period. Yields are generally heavier than determinate types, but fruit are usually later to mature. Indeterminate tomatoes are large, sprawling plants which often perform best when grown in wire cages or trained on stakes. 

What are some good tomato varieties for Iowa? 

Suggested tomato varieties for Iowa include ‘Jet Star’ (indeterminate plant; red, oblate, medium to large fruit), ‘Better Boy’ (indeterminate; red, round, medium-sized fruit), ‘Celebrity’ (determinate; red, oblate, medium to large fruit), ‘Big Beef’ (indeterminate; red, oblate, large fruit), ‘Red Sun’ (determinate; red, globe-shaped, large fruit), ‘Carolina Gold’ (determinate; golden orange, oblate, large fruit), ‘Pony Express’ (determinate; red, plum-shaped fruit), ‘Sweet Olive’ (determinate; red, oval, grape-type fruit), and ‘Golden Sweet’ (indeterminate; yellow, oval, grape-type fruit). Oblate fruit are roundish with slightly flattened tops and bottoms.

When purchasing tomato plants, are big or small plants better? 

When purchasing tomato plants at your local greenhouse or garden center, select stocky, dark green plants. Plants should be 6 to 10 inches tall with stems about pencil-size in thickness. Avoid large plants with flowers and fruit. Early fruit development will stunt plant growth and reduce total yield. 

I have started several tomato plants indoors. Can they be planted directly into the garden? 

Plants started indoors or purchased at a greenhouse should be hardened or acclimated to outdoor conditions before transplanting into the garden. Initially place the plants in a shady protected location, then gradually expose them to longer periods of sunlight. After several days of hardening, the tomatoes should be ready to be planted into the garden. 

When can I plant tomatoes in Iowa? 

Transplant tomatoes into the garden after the danger of frost is past. In central Iowa, it’s usually safe to plant tomatoes around May 10. Gardeners in southern Iowa can plant one week earlier, while those in northern areas should wait an extra week. The last practical date for planting tomatoes is approximately June 20. 

What is the proper way to plant tomatoes? 

Tomatoes perform best when grown in fertile, well-drained soils in full sun. Soil structure and drainage of heavy, clay soils can be improved by incorporating organic matter, such as compost or peat, into the soil. Raised beds are another option for gardeners with heavy, clay soils. Planting sites should receive at least six to eight hours of direct sun daily. 

If the plants are in peat pots, tear off the top edge or make sure the top edge is well below the soil surface once planted. If the top edge of the peat pot is exposed to the air, it will act like a wick and draw moisture from the soil around the plant’s roots. If the tomatoes are in plastic pots or cell-paks, carefully tap out the plants. Use a sharp knife to cut around plants growing in small flats. 

Set plants into the soil up to their first true leaves. Pinch off the bottom leaves of tall, lanky transplants and lay them sideways in a trench. Carefully bend the stem upward so that the upper few inches of the stem are above the soil surface. Roots will develop all along the buried stem. 

Spacing of plants depends on the growth habit of the variety and training system employed. Indeterminate varieties that are staked can be planted 1½ to 2 feet apart in the row. Indeterminate plants grown in wire cages should be spaced 2½ to 3 feet apart, while a 3- to 4-foot-spacing would be appropriate for indeterminate tomatoes allowed to sprawl over the ground. Determinate, ground-grown tomatoes can be planted two feet apart. Rows should be spaced about four feet apart.