Ultimate Guide To Growing Tomatoes Indoors

Growing tomatoes indoors can be difficult but it is also a great way to ensure a fresh supply throughout the colder months. Many people continue growing during the colder months because supermarket purchased fruits often lack the great flavor of home grown varieties.

This is also a great option for gardeners in colder USDA planting zones. In the coldest areas frosts may continue into April or May. This can make growing warm weather crops such as tomato plants in the garden almost impossible. Growing tomatoes indoors or undercover is a great way to get around this problem.

1 Growing tomatoes indoors is a great way to ensure a supply of fresh fruit throughout the year
This is a great way to ensure a supply of fresh fruit throughout the year. It is a particularly useful method for gardeners in colder or difficult climates. Here cultivation undercover enables gardeners to better control the temperature and conditions surrounding their plants.

If you want to try growing tomato plants indoors this guide is for you. We will discuss everything you need to know, from choosing the right variety to positioning your plants right up until harvest.

What Tomato Varieties Should I Use?

In order to enjoy success it is important that you select the right type of plant. Strictly speaking there is no reason why any variety of tomato can’t be successfully cultivated undercover. However some varieties and types will be easier than others.

Smaller varieties such as cherry or plum are preferable. These produce smaller fruits and are quicker to ripen. They also tend to produce heavier yields than other varieties.

Select indeterminates if possible. Determinate tomatoes tend to be smaller shrub varieties but these will fruit for only a few weeks and then stop. Indeterminate varieties continue to fruit throughout the winter.

Heirloom variety Ping Pong produces ping pong sized, cherry-pink fruit within 75 days. Baxter’s Early Bush is a determinate variety that is quick to ripen, about 70 days. Tommy Toe is an indeterminate heirloom. Maturing in about 70 days this is a disease resistant, reliable variety.

2 While most varieites can be grown undercover your own situation will in part dictate your choice
While most varieties can be grown undercover your own situation will, in part, dictate your choice. Gardeners with limited space will benefit from cultivating compact, shrub varieties. However if you want to grow tomatoes indoors in a greenhouse or larger space you will be able to cultivate larger vining varieties. 

Hybrid varieties are also suitable to grow tomatoes indoors. Red Robin is quick to mature, within 55 days, and produces cherry red fruit. Red Robin is a popular choice. Not only is it a reliable variety but it is able to set fruit in cooler temperatures.

Determinate variety Micro Tom may take slightly longer, up to 85 days, but produces red, dwarf fruit. Another popular hybrid determinate is Totem. Maturing in 70 days it reliably produces crimson red cherry fruit.

If you want something slightly more dramatic, and have the space to commit to grow tomatoes indoors, why not try a hanging variety to produce fruit. Planted in hanging baskets these will drape down to the floor, placing their attractive fruit firmly at eye level. Burpee Basket King produces attractive red fruit while Yellow Pear produces rich, golden tomatoes.

How to Grow Tomatoes Indoors

Sow tomato seeds a quarter of an inch deep in 6 inch pots filled with seed starter mix. Place the pots in a warm position, such as on top of the fridge. Keep the soil lighty moist until germination occurs.

If you are growing determinate varieties sow fresh seeds every two weeks. This allows you to enjoy a regular supply of fresh fruit.

Germination will occur within 10 days.

After seedlings have emerged place the pots in a brightly lit area. Close to a south facing window is ideal. Successfully growing indoor tomatoes requires at least 8 hours of light a day. Less than this and the plants may fail to produce any fruit. Use a grow light if there is not enough sun.

Make sure the pots aren’t in a draft. Temperatures should average at least 65℉. If you don’t have a light enough position you will need to place the plants under grow lights.

3 Germination requires a warm position with plenty of light
Germination requires a warm position with plenty of light. If you can’t provide these conditions naturally you will need to use artificial methods such as grow lamps and heaters. 

When the seedlings reach a height of 3 inches transplant into larger pots. These should be at least 12 inches deep. They should also be clean, have drainage holes in the bottom and be unglazed. Unglazed pots are able to breathe, this helps the soil and plant to maintain a healthy balance.

Fill with fresh potting soil or general purpose soil. You can also make your own by combining an equal mix of compost, vermiculite and peat moss.

Make a hole in the soil large enough to hold the plant. Carefully remove the young plant from the small pot. Place it in the hole and gently firm down the soil around the plant.

If you are growing a larger variety you will also need to install a stake or tomato cage for support. After transplanting water well and return to the light location.

Growing Tomatoes Care Tips

As long as the plants are in a light spot, caring for growing indoor tomatoes is largely the same as caring for any other houseplant.

Growing indoor tomatoes also means that they are protected from many of the pests and problems that can affect outdoor plants.

Temperature and Light

Keep the temperature warm, this will not only promote growth but also flowering. An average of 75-85℉ is ideal.

As we have already noted tomato plants require lots of light in order to flower. Placing close to, or in, a south facing windowsill will provide the plants with plenty of light. To ensure the maximum amount of light reaches the plants consider painting the walls around the plant white. This helps to reflect heat and light back to the plants.

If you are unable to provide ample light, a grow lamp or even a general purpose lamp can be used. These will top up natural light levels with artificial light and heat.

Watering and Feeding

Water regularly. Keeping the soil consistently moist helps to prevent the tomatoes from splitting. A light organic mulch around the base of the plant will help moisture retention.

If you are unsure of when to water a soil moisture gauge can be used. Alternatively place a finger in the soil. If the soil feels dry you know it is time to water the plants.

Fertilise your plants every week. Tomato feed can be used as can fish emulsion or liquid kelp. Homemade solutions, such as vermicompost tea, can also be applied. Using organic and homemade solutions enable you to know exactly what you are giving your plants.


Larger varieties will require staking. Alternatively you can use a tomato cage. Support helps to keep the plant tidy while also preventing it from toppling over when heavy with fruit.

If you are growing large vining varieties, or trailing varieties training the vines along an indoor frame or trellis helps to keep the plants neat. It also helps to prevent them from being accidentally damaged.

4 Care for tomatoes growing indoors as you would outdoor plants

Care for tomatoes growing indoors as you would outdoor plants. Water and feed on a regular basis. You will also need to provide sturdy support. This is particularly important when the plants are fruiting. At this stage they tend to become top heavy and prone to toppling. 

How to Prune Tomatoes

Determinate varieties as well as most shrub and smaller or compact varieties don’t require pruning.

Larger, vining and trailing varieties will benefit from pruning. Here pruning helps plants to focus on flower and fruit production. It also helps to prevent them from overcrowding a potentially small space.

Tomato suckers are shoots that form in the axis where the side branches emerge from the central stem. Pruning all the suckers below the first flower cluster will help to keep plants tidy while also encouraging flower and fruit production. Remove these suckers with a pruning shears, scissors or simply by pinching them away.

Pollination Help

The tomato flower is perfect. This means that it has both female and male parts. Consequently the flowers are self-pollinating. This means that you do not need to do anything in order to get fruit to form.

If you want to help the pollination process, gently shake the stems every day. Alternatively place a small oscillating fan near the plants. This imitates a gentle breeze and can encourage pollination.

Continue to care for your plants as you would if they were growing outside. When fruit has formed and is ripe it can be picked and enjoyed.
5 Similar to outdoor cultivation with ample light water and heat growing tomatoes indoors is a satisfyingly easy process
Similar to outdoor cultivation, with ample light, water and heat growing indoor tomatoes is a satisfyingly easy process. With a little care and attention you will be able to cultivate healthy, heavy cropping plants that provide you with fresh fruit throughout the year. 

As long as you choose the correct variety and position you will find that growing indoor tomatoes is largely the same as outside cultivation.

Growing indoor tomatoes is a great way to enjoy their fresh fruit if you are gardening in overly cold or warm climates. Undercover cultivation gives you a greater degree of control over the elements your plants are exposed to. For other gardeners growing indoor tomatoes is simply a great way to continue enjoying the plant’s fresh fruit throughout the year.

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