How to Grow Tomatoes Indoors

indoor tomato plant under grow lights

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Once you've had a fresh, flavorful tomato from your garden, it's hard to go back to supermarket tomatoes once the growing season is over. The good news is it's possible to grow tomatoes (Solanum lycopersicum) indoors all year long. With good artificial lighting or a bright enough window, you can grow tomatoes in your home even during the wintertime.

There are many types of tomatoes to choose from. The small patio tomato varieties are best for indoor growth, as their containers won’t take up that much space. Likewise, determinate tomato plants generally do not get as large as indeterminate plants. However, determinate plants produce all their fruit at once whereas indeterminate plants regularly set and ripen fruit. So to have a consist supply of tomatoes with determinate plants, plant a few varieties that fruit at different times or sow new seeds every month or two. Tomato plants generally have a fast growth rate. Outdoors, they should be planted in the spring after the threat of frost has passed. But indoors, you can try planting them at any point.

Botanical Name Solanum lycopersicum
Common Name Tomato, heirloom tomato
Plant Type Annual, vegetable
Mature Size 3–6 ft. tall, 2–3 ft. wide
Sun Exposure Full
Soil Type Loamy, well-drained
Soil pH Acidic, neutral
Bloom Time Summer
Flower Color  Yellow
Hardiness Zones 10-11 (USDA)
Native Area  South America, Central America
Toxicity Toxic to people, animals

Tomato Care

A container that is at least 12 inches deep should be sufficient for most tomato plants. But check the space requirements for your specific variety. The container must have ample drainage holes, or the plant can develop root rot from soil that stays wet for too long. An unglazed clay container is ideal because it also will allow excess moisture to escape through its walls.

When planting seeds indoors, plant them about 1/4 inch deep in a shallow growing tray filled with seed-starting mix. Once seedlings pop up, transfer them to small pots. When planting a young tomato plant, bury the stem up to the bottom set of leaves. Roots will form all along the stem, resulting in a stronger plant. If your tomato plant variety requires support, install a stake or tomato cage in the container.

Tomatoes are self-pollinating plants, meaning they don’t need insects to pollinate for them. However, you can help your indoor plants by mimicking the wind that would naturally fascinate their pollination process. Gently shake the stems every day or so when the plants are in bloom, or place a small oscillating fan in the area to act like wind.

Light

Tomato plants like a lot of light. So when growing them indoors, aim to place them by your brightest window. A large south-facing window is ideal. If you don't have a window that will work, install plant grow lights above your tomato plant containers.

Soil

Tomatoes thrive in an organically rich, loose soil with a slightly acidic to neutral soil pH. For container plantings, choose a quality all-purpose organic potting mix. A mix made especially for vegetables often works well.

Water

These plants also like a lot of water. Aim to keep the soil lightly moist but not soggy. A consistent level of moisture will help to prevent the tomatoes from splitting. So check often to see whether your containers need water. If the soil feels dry about an inch down, it’s time to water.

Temperature and Humidity

One easy part about growing tomatoes indoors is they like average room temperatures between around 65 and 80 degrees Fahrenheit. Humidity also typically isn’t an issue indoors. Just be sure to protect your plants from drafts, as well as air flow from heating and cooling vents. 

Fertilizer

Tomatoes are heavy feeders. Use an organic slow-release fertilizer on your plants, following label instructions. 

Are Tomato Plants Toxic?

The ripened fruit of tomatoes is not toxic to people or animals. However, the stems, leaves, and roots all contain a compound called solanine, which is toxic to people and animals when ingested. Animals typically have more of an issue with it than people do.

Symptoms of Poisoning

Symptoms of toxicity in both people and animals include vomiting, diarrhea, stomach pain, drooling, lethargy, and confusion. If you suspect poisoning, contact a medical professional as soon as possible. 

Tomato Varieties

There are many tomato plant varieties that come in different fruit sizes, appearances, tastes, and more. They include:

  • Beefsteak Red: This plant features large tomatoes with a bright red color and thick flesh. The plants grow quite large and typically need staking or other support.
  • Cherry: This variety yields lots of small tomatoes that are especially juicy and flavorful. 
  • Roma: The fruit from this plant is often used in sauces and pastes. The tomatoes are egg-shaped and more fleshy than juicy.
  • Patio: This is a small hybrid variety that’s ideal for containers. The tomatoes are compact but flavorful, and the whole plant only grows to around 2 feet tall.