How to Grow and Care for Tomatoes Indoors

Successfully growing tomatoes indoors is achievable, but it is difficult if you do not mimic their outdoor growing conditions. Tomatoes (Solanum lycopersicum) usually grow outdoors in warm climates with long growing seasons, taking as much as three months for seeds sown outdoors to mature into fruit-producing plants. Tomatoes grown indoors need bright light and heat; otherwise, it's hard for them to grow during winter when sunlight is scarce and temperatures drop.

All members of the nightshade family, including tomatoes, contain substances in the green plant parts (i.e., the leaves, stems, and roots) that are toxic to people and pets, so care should be taken not to allow cats, dogs, or curious children to nibble on the plants.

Can You Grow Tomatoes Indoors?

Yes, tomatoes can be grown indoors. Growing tomatoes indoors is ideal in the winter when it's too cold for them to grow outdoors. The small patio varieties are best for growing indoors because it's easy to find a container that is large enough to accommodate their height and root system.

Tomatoes require a warm spot with full sun, so make sure you have a place indoors by a window that gets plenty of sunlight. If not, you'll need to acquire some grow lights. Provide them with plenty of water and protect them from strong drafts.

How to Grow Tomatoes Indoors

Tomatoes are not a common indoor plant, but they can be grown inside if you take care to provide conditions that are very similar to an outdoor summer garden:

• You can plant them anytime and stagger their planting time to get regular harvests.
  
• Tomatoes indoors need a warm, bright spot.
• Grow lights often will be necessary to maintain sufficient light.
• Protect tomatoes grown indoors from strong drafts.
  

Sunlight

Tomato plants require full sun, meaning six to eight hours of direct sunlight on most days. Indoors, the ideal spot is a bright, south-facing window.

Rotate the pots every day until the seedlings begin to flower and set fruit. Turning the pots so the other half of the plant faces out the next day will prevent the stems from becoming leggy and too flimsy to support fruit. In northern regions where winter days are short, you may need supplemental artificial light to grow tomatoes.

Artificial Light

If you don't have a sunny window that provides bright light for at least six hours, install grow lights above the tomato plant containers. It helps to have a mechanism for raising and lowering the lights. This feature will prevent the plants from becoming too leggy by stretching toward the light. The ideal position for lighting is about 1 to 2 inches above the tops of the seedlings until they begin to flower and fruit.

Temperature and Humidity

One easy part about growing tomatoes indoors is they like average room temperatures, usually between 70 and 80 degrees Fahrenheit. Grow lights can help keep plants warm if your house generally falls below this threshold. Humidity typically isn’t an issue indoors.

Watering

Tomato plants like a lot of water. But they do not like wet feet, so good drainage is essential. Aim to keep the soil lightly moist but not soggy. A consistent level of moisture will help to prevent the tomatoes from splitting and prevent blossom end rot. Inspect the containers often to see if the plants need water. If the soil feels dry about 1 inch down, it’s time to water.

Air Circulation

Indoor tomatoes must be protected from strong drafts but still need some air circulation to prevent fungal problems.

Fertilizer

Tomatoes are heavy feeders. Use organic slow-release tomato fertilizers on your plants, following label instructions. Potted tomatoes typically need a bit more feeding than outdoor in-ground tomatoes.

Pruning and Maintenance

Pruning tomato plants isn’t essential, but it can help them to be more fruitful. Determinate varieties should never be pruned. Prune off small stems growing from the main stem on indeterminate varieties. These small “suckers” won’t bear much fruit. By removing them, you’ll encourage the plant to produce more full-grown fruit rather than foliage.

Pollination

Tomatoes are self-pollinating, meaning they don’t need insects for pollination. But they will need hand pollinating when grown indoors or an oscillating fan to mimic wind conditions that would normally spread pollen between blooms.

To hand pollinate, gently shake the stems every day or so when the plants bloom or touch each blossom with a cotton swab to move pollen from one bloom to the next.

Container and Size

A suitable container is essential for growing tomatoes indoors. The container must be at least 1 foot in diameter and depth, but bigger is better. In general, the larger the tomato, the larger the pot you will need to achieve a harvest. Check to see how much space your particular variety needs.

Potting Soil and Drainage

Tomatoes thrive in an organically rich, well-draining soil with a slightly acidic to neutral pH. For container plantings, choose a quality, all-purpose organic potting mix.

Potting and Repotting Tomatoes

When planting purchased seedlings, place them in the pot just slightly deeper than they were in the seedling container so that a portion of the stem is buried.

Once established, tomato plants don't like their roots disturbed. So, rather than repotting as the plant grows, select a container large enough to accommodate your plant's mature size.

Moving Tomatoes Outdoors for the Summer

Considerations

Tomatoes are warm-season plants. Do not move them outdoors until the weather is reliably warm. When nighttime temperatures stay above 50 degrees Fahrenheit and daytime temperatures are reliably in the upper 70s, it is safe to move them outdoors for the summer.

To avoid the shock of a sudden move, harden off potted tomatoes by giving them increasingly extended visits outdoors over about a week. For the first full day or two outdoors, give tomatoes a partly shaded location before moving them into the full sun conditions they prefer.

When to Bring Tomatoes Back Inside

Potted tomatoes that have been moved outdoors should be moved back inside before nighttime temperatures fall below 50 degrees Fahrenheit. Tomato plants crave warmth and do not react well to cold temperatures.

A tomato plant can become quite large during a summer spent in ideal conditions. It's OK to give the plant a pruning before bringing it indoors. Some experienced growers prefer to take cuttings to propagate a piece of the plant indoors for the next season rather than move an enormous plant indoors.