Tomatoes (Solanum lycopersicum) are one of several stalwart plants in the nightshade family that are essential plants in edible gardens. Tomatoes are best suited for outdoor growing in warm climates with long growing seasons since it can take as much as three months for seeds sown outdoors to mature into fruit-producing plants. This is one reason why it's tempting to grow them indoors if possible—to turn the fruit-producing season into a year-long affair rather than an end-of-summer harvest. Once you've eaten a fresh, flavorful tomato from your garden, it's difficult to go back to supermarket tomatoes. But because tomatoes crave bright light and heat, they can be hard to grow during winter months when sunlight is scarce. Successfully growing tomatoes indoors requires some specific conditions.
While it is usually not a problem outdoors, 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?
Tomatoes are not a common indoor plant, but they can be grown there if you take care to provide conditions that are very similar to an outdoor summer garden. Tomato plants are typically planted in the spring after the threat of frost has passed. But indoors you can start them anytime, as well as stagger their planting time to get regular harvests. When grown indoors, tomatoes need a warm, bright spot for their container. Grow lights often will be necessary to maintain sufficient light, as winter light is typically somewhat dim and short-lived, even in the brightest windows. And indoor tomatoes must be protected from strong drafts, but must have enough air circulation to prevent fungal problems.
There are many types of tomatoes to choose from. 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. Determinate tomato plants generally do not grow as large as indeterminate plants. However, determinate plants produce all their fruit at once whereas indeterminate tomato plants continuously set and ripen fruit. In order to have a consistent supply of tomatoes with determinate plants, plant a few varieties of that fruit at different times, or sow new seeds every month or two.
There are numerous types of tomato plants that produce different fruit sizes, appearances, and flavors. Plants that produce abundant but smaller fruit are easier to manage indoors. Some tried-and-true favorites include:
- 'Sun Gold': This is an indeterminate, thin-skinned, bite-sized, yellow variety with very sweet, round fruit.
- 'Jelly Bean': This indeterminate variety features heavy clusters of up to 30 fruits that weigh 1/4 to 1/2 ounce each; it comes in both red and yellow fruits.
- 'Tommy Toe': This indeterminate heirloom cherry type is round or oval in shape, and the fruits weigh about 1/2 to 1 ounce each.
- 'Pear': This is an indeterminate cherry type with red or yellow pear-shaped fruits; it has prolific yields of fruit each weighing between 3/4 and 1 ounce.
- 'Juliet': This is an indeterminate tomato with glossy red fruits that are just a bit bigger than many cherry varieties at 1 ounce each.
How to Grow Tomatoes Indoors
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. Rotating the pots will prevent the stems from becoming leggy and too flimsy to support fruit. In northern regions where winter days are short, you may have trouble growing tomatoes without supplemental artificial light.
If you don't have a sunny window that provides enough light, install grow lights above the tomato plant containers. It helps to have a mechanism for raising and lowering the lights. This will prevent the plants from becoming too leggy by stretching up 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 between around 70 and 80 degrees Fahrenheit. Humidity typically isn’t an issue indoors.
Tomato plants like a lot of water. But they do not like wet feet, so good drainage is important. 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.
Be sure to protect your plants from strong drafts, as well as temperature extremes from heating and cooling vents. Winter air is typically fairly dry, but if you live in a very humid climate (such as coastal areas) indoor tomatoes may be susceptible to fungal problems. In these conditions, running a dehumidifier, or even just keeping a small fan running in the growing area, may help.
Tomatoes are heavy feeders. Use an organic slow-release fertilizer 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 not be pruned. But you can prune off some of the small stems growing from the main stem on indeterminate varieties. These small “suckers” won’t bear much fruit. So by taking them off, you’ll encourage the plant to produce more fruit rather than foliage.
Tomatoes are self-pollinating, meaning they don’t need insects for pollination. However, you need to ensure indoor pollination by using one or more of these methods: Gently shake the stems every day or so when the plants are in bloom; touch each blossom with a cotton swab to move pollen from one bloom to the next; or place a small oscillating fan in the area to serve as a wind source.
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 soil pH. For container plantings, choose a quality all-purpose organic potting mix. The container also must have ample drainage holes to avoid root rot from soil that stays wet for too long. An unglazed clay container is ideal because it also allows excess moisture to escape through its walls. For indoor growth, you'll need a tray under the container to catch water from the drainage holes. Empty the tray as soon as it fills up to prevent the roots from sitting in water. Use a tomato cage, stakes, or other support structure to help support the plant.
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
Tomatoes are warm-season plants, so don't 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, it's best to harden off potted tomatoes by giving them increasingly long visits outdoors over a period of about a week. For the first full day or two outdoors, it's best to give tomatoes a shady location before moving them into the full sun conditions they crave.
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. Remember that tomatoes crave warmth and do not react well to cold temperatures.
However, a tomato plant can become quite large during a summer spent in ideal conditions, so it's best to give the plant a good short haircut before bringing it indoors. Some experienced growers find that it makes more sense to take cuttings to propagate rather than moving an enormous plant indoors.
Are there pests and diseases that affect indoor tomatoes?
Tomato plants are susceptible to several pest and disease issues. However, indoor growth can help to protect them from many of these issues. Still, be on the lookout for blossom end rot, which can occur from a calcium imbalance. Aphids and other common plant pests might also find their way indoors and infest your plant. Plus, uneven watering can result in fruit that splits.
How do I harvest indoor tomatoes?
The time between planting and harvesting varies among tomato varieties. In general, most are ready to harvest somewhere between 55 and 85 days. You’ll know it’s time when the fruit has developed its color and it comes off the vine easily. Gently pull the fruits off the vine, and store them at room temperature. Putting them in the refrigerator can negatively impact the flavor and texture. Aim to use them within a few days. You can eat them fresh or cooked. They also can be canned, turned into sauces, oven-dried, and more.
How do I start tomatoes from seed?
When sowing tomato seeds indoors, plant them about 1/4 inch deep in a shallow growing tray filled with seed-starting mix. Artificial light (grow lights) and heat mats are key elements to success because tomato seeds require warm soil to germinate. The soil should be at least 60 degrees Fahrenheit at all times.
Once seedlings emerge and develop at least two sets of true leaves, transfer the seedlings to small pots. When they reach about 4 inches tall, plant them in their permanent large container. When planting a young tomato plant, remove the bottom set of leaves, and bury the stem up to the new bottom set of leaves. Roots will form all along the stem, resulting in a stronger plant.
Can I propagate tomatoes myself?
Most gardeners grow tomatoes from nursery plants or from seed. But you also can propagate them via cuttings. This allows you to create an exact copy of a particular tomato plant you like. Late spring is the best time to take a cutting, though it can be attempted at any point with indoor-grown tomatoes. Here’s how:
- Select a sucker coming off the main stem, and cut off a portion that’s 6 to 8 inches long.
- Remove any buds or flowers on the cutting, along with the leaves on the lower half of the stem.
- Plant your cutting in a small container filled with soilless potting mix, and evenly moisten the mix. Place it in a warm spot with bright, indirect light.
- Keep the mix moist. Roots should develop within two weeks. You’ll know they have strong roots when you can gently tug on the cutting and feel resistance.