Compared to greens, root vegetables and plants in the cabbage family, tomato ( Solanum lycopersicum) plants take up more space in the vegetable garden. These robust plants need a minimum of 12 inches of space, but most varieties grow between 2 and 3 feet wide and have deeper roots, as well. The extra space requirements are a small price to pay for the taste of fresh, homegrown tomatoes.
How big a tomato plant gets depends mostly on the type and variety of the plant. Compact, dwarf tomato plants, such as 'Better Bush' and 'Small Fry,' are usually determinate, meaning the plant is a hybrid that grows to a certain size and then stops. These plants grow well in containers because they usually grow 24 inches wide or less. Indeterminate varieties are sprawling, tropical plants that will grow until frost, disease or poor growing conditions kill them. In mild climates, they may grow to 6 feet tall and may sprawl along the ground to 6 feet wide. Heirloom varieties, such as 'Brandywine' or 'Cherokee Purple' tend to spread out unless staked or caged. The root system of a tomato plant might extend to as much as 2 feet deep, but the main portion of the root system lies in the first 12 inches under the soil. Because the roots lie close to the surface, it is important to dig carefully around tomato plants so you don't damage the roots.
How you care for your tomatoes plays a role in how deep and wide they grow. Plants that are pruned and staked tend to stay fairly compact, while tomatoes that are left to spread on the ground can reach 6 feet wide or more. Nitrogen fertilizer promotes lush green growth. Under dry conditions, the roots burrow deeper into the soil in search of moisture. Container-grown tomato plants might have smaller roots simply because they have less space to grow.
In addition to the care you give tomato plants, weather conditions, soil and other environmental conditions play a role in the size of tomato plants. Growth slows during dry, hot weather as well as cold, rainy weather. Tomatoes grow best in slightly moist, loam soil. In heavy clay soils, growth might be slow because the plants' roots can't access adequate oxygen. Herbicide injury, caused by accidental exposure to weed killers, can cause stippled, twisted leaves and slow growth. Finally, tomato diseases, such as fusarium wilt and verticillium wilt, cause distorted, slow growth, leaf drop or damage and finally, death of the plants.
When planting tomatoes, give them adequate space. If you plant them too closely together, they are more prone to diseases and produce a smaller harvest. They are also more difficult to care for. Plant dwarf plants 12 inches apart and space staked plants 15 to 24 inches apart. Plants in cages or those growing on the ground should be spaced two to three feet apart. Very vigorous varieties, such as 'Supersteak,' may need up to six feet between plants. To provide adequate room for root growth, till the soil to a depth of at least 8 to 12 inches. Amend heavy soils with compost or manure to improve the texture and drainage. Grow tomatoes in containers that hold at least 5 gallons of potting soil to allow adequate room for the roots.