How to Care for an Indoor Tomato Plant

Most gardeners bid a fond farewell to their homegrown garden tomatoes (Lycopersicon esculentum) at the end of the summer when cold weather approaches. Tomato plants are typically grown as annuals, because they're only winter hardy in U.S. Department of Agriculture plant hardiness zones 10 through 11. It's possible, however, to care for a tomato plant indoors year-round -- even during the winter -- and enjoy the "fruits" of your labor when snow is on the ground.

The key is providing the plant with suitable indoor growing conditions.

Tomato plants grow best in full sun, which means at least six to eight hours of direct sun each day. Unfortunately, this requirement is typically the deal-breaker for being able to grow tomatoes indoors. But if you have a glassed sun porch, Florida room or another room that receives this much incoming sun, you've hurdled the first obstacle.

A "plant dolly" may allow you to meet an indoor tomato plant's full sun requirement. Simply roll the plant across a room to keep it in the sun's path as the sun moves across a room during the day. Although it's a bit labor-intensive, your craving for homegrown tomatoes may outweigh the work involved.

A plant will grow toward the light from a nearby window. A plant dolly also allows you to turn the plant so all its parts receive sun exposure.

Tomato plants like moist soil but not waterlogged soil. If you keep the soil soggy, the roots may rot or the plant may actually drown. Water when the top 1 inch of the soil is dry.

A rule of thumb is to use at least one 3-gallon container for each tomato plant -- at least 14 inches in diameter. You can also use a clean 5-gallon bucket from your local garden center. Don't use a bucket that formerly held chemicals. Regardless of which type container you use, make sure it has drainage holes in the bottom.

To produce a lot of fruit, a tomato plant needs fertilizer. You can use a slow-release synthetic formula, such as a 9-4-12 blend you apply once every three months. Follow the label directions for container tomatoes based on pot diameter; for example, apply 8 tablespoons of fertilizer for a 14-inch pot. Sprinkle the fertilizer on the soil around a plant, keeping it away from the stem and off the foliage. You can also use an organic fertilizer formulated for tomatoes, such as a 3-4-6 blend. Typically, you apply organic fertilizers more often than synthetic products; for example, every two weeks, mix 1.5 tablespoons of fertilizer per 12-inch pot and work it into the soil around a plant.

Don't begin fertilizing tomato seedlings until they have their first set of "true leaves."

Bush-type (determinate) tomato plants typically work best for indoor culture because they don't grow as large as vining-type (indeterminate) plants. Either type benefits from staking or caging, which provides support for a growing plant. Gently press a tomato cage, a bamboo cane or a spiral stake into the soil of the container. As the tomato plant grows, tie it to the cane or stake with soft fabric, or guide its branches through the metal grid of a cage.

A bush-type tomato usually doesn't need pruning because its size is more manageable. If you're growing a vining tomato, you may need to prune it to keep it in bounds indoors. Prune the suckers, the stems that grow between the main stem and the lateral stems, by cutting them with sterilized pruning shears or scissors.

Sterilize pruning tools by soaking the blades for five minutes in a solution of 1 part household pine-oil cleaner to 3 parts water. Remove them from the solution and rinse thoroughly with water or let them air-dry before cutting plants.

When a tomato plant sets flowers outdoors, the wind carries pollen grains from flower to flower. Without this pollination, the flowers aren't fertilized, which means they cannot develop into fruit. Indoors, simply tap the flowers or shake plants gently to help move the pollen from flower to flower.

An advantage of container tomato plants is that you won't have to contend with weeds. Another advantage of growing plants indoors is they are not exposed to many insect pests that attack plants outdoors. Occasional indoor pests may include whiteflies and spider mites, both of which can be controlled by spraying them with a premixed, ready-to-use horticultural soap.