How To Grow Tomatoes Indoors – A Step By Step Guide For Growing Tomatoes From Seeds

How to grow tomatoes indoors: ripe fresh tomatoes growing on the vine

Tomatoes are delicate, tropical plants. They require 6 to 8 hours of direct sunlight every day, consistent warmth, and frequent watering. Also, depending on the type of tomatoes you grow, you will need to prune regularly and stack. Tomatoes are also susceptible to various diseases and pests and require special care. Here in this article, we will teach you how to grow tomatoes indoors from seeds.

Growing tomatoes can be quite rewarding. With a little work, you can get a good supply of fresh, highly nutritious tomatoes. With keen attention to the growing requirements for tomatoes, you will have a bountiful harvest. You can even grow tomatoes all year round indoors as long as you provide favorable conditions.

This article discusses how to grow tomatoes indoors and will provide you with the steps and tips for starting your plants from seeds and caring for your tomato crops.

Types Of Tomatoes To Grow Indoors

How to grow tomatoes indoors

The first decision you need to make is on the type of tomatoes to grow. The right tomato variety will depend on factors such as the season, available space, your level of gardening expertise, and preference.

Tomatoes can be classified broadly according to their size, use, and growth habit as follows:

  • Beefsteak. These are large succulent tomatoes. They are mostly used for cooking and to make salads and sandwiches. They take a longer time to grow in longer warm seasons. They are also commonly grown in greenhouses and polytunnels.
  • Plum. Plum tomatoes are not ideal for fresh eating. They are used for canning and making pasta sauces and ketchup.
  • Cherry. A cherry tomato is a small, round, fruity variety. They are flavorful and are used for both cooking and in salads.
  • Indeterminate tomato/cordon tomato varieties. Typically, these tomatoes have a single stem and grow quite tall. They require stacking on twine or bamboo for support. They develop side shoots that grow into large lateral branches. The branches require regular pruning to prevent the tomato plant from becoming congested resulting in a low yield. Indeterminate tomatoes set and fruit continuously to offer a consistent supply of tomatoes.
  • Determinate tomato/bush tomato varieties. These are low growing tomatoes with a sprawling habit. They are suitable for growing tomatoes in small spaces such as containers, hanging baskets, mini polytunnels, or under cloches. They do not require regular pruning as the side shoots stop growing by themselves. The fruits are smaller and ripen early on in the growing cycle. They fruit once in their lifecycle.
  • Dwarf varieties. These are small tomato plants that are best grown in containers or small covered raised beds.

Best Varieties of Tomatoes to Grow Indoors

Below is a list of the tried and tested varieties of indoor tomato plants:

  • Sungold
  • Jelly Bean
  • Supersweet 100
  • Pear
  • Jaune Flamme
  • Juliet
  • Green Zebra
  • Tommy Toe
  • Red Robin
  • Toy Boy
  • Florida Petite
  • Tiny Tim

How To Grow Tomatoes from Seeds

How to grow tomatoes indoors: planting tomato seeds
Source: Shutterstock

1. Choose the right time to plant your seeds

The best option for starting your indoor tomato seeds is indoors, 6 to 8 weeks before the last spring frost. Although the temperature outdoors is still cool, growing your tomato seeds indoors helps to maintain the optimal soil temperature for germinating tomato seeds (65-860 F). However, if you have the right equipment such as grow lights and heaters, you can grow tomato seeds any time throughout the year.

2. Determine and acquire suitable growing containers

You can either plant the seeds in individual pots or growing trays, which are readily available in garden supply stores. The growing containers should have drainage holes to ensure adequate aeration and water flow.

3. Fill the containers with potting mix

Use a light, sterile potting mix to ensure that the soil is well aerated and drained. Mix equal parts of peat moss, coarse vermiculite, and compost.

4. Sow the seeds

Begin by watering the soil. Then plant each tomato seed ¼ inch deep and 2 inches apart. Each pot can accommodate 2-3 seeds. If planting on a tray, create ¼ inch deep rows in the soil where you will plant the seeds. The rows should be 2 inches apart. Drop seeds in each row, 2 inches apart from each other. Cover them with soil and pat the soil down lightly.

If you are planting more than one variety of tomato seeds, use different containers for different varieties. You may also plant each variety in its own row and label them accordingly.

5. Provide adequate temperatures and lighting for germination

Place the growing container near a large window to expose the seeds to direct sunlight. Alternatively, use a fluorescent grow light to provide 6-8 hours of light each day and to keep the soil warm. You can also place a heating mat beneath the pot or tray to increase the germination rate.

6. Water the seeds regularly

Mist the seeds daily using a spray bottle. The idea is to keep the soil moist but not clogged up. Watering is especially crucial in the first 7-10 days after planting.

7. Keep an eye out for the sprouts

They should come up within 2 weeks. Once the seeds have germinated, reduce the watering frequency to prevent the roots of the seedlings from rotting.

8. Provide a gentle breeze over the seedling

If there is no wind coming in through a window, run an electrical oscillating fan at a low setting near the germinated seedlings to strengthen their stems.

Transplanting Tomato Seedlings

1. Prepare the seedlings for transplanting

The seedlings are ready for transplanting within 2 weeks of germinating – they should be at least 6 inches tall. It is important to harden off the young plants before repotting them.

One week before transplanting, move the plants to a partially shaded area. Within the week, gradually expose the seedlings to more hours of direct light and outdoor temperatures.

2. Choose a planting container and site

You can grow tomatoes indoors in containers that are at least 12 inches deep. For example, hanging baskets, pots, and grow bags. You could also use barrels or old wooden crates. Avoid metallic crates as they are likely to rust and pass iron into the soil compromising its pH level. You require larger containers for indeterminate tomatoes.

Since tomatoes require direct sunlight and warmth, whichever site you choose should have direct exposure to the sun for 6-8 hours each day. Preferably, near a south-facing large window.

3. Prepare the transplant container

A single tomato plant can produce hundreds of fruits, so they require highly fertile soils to flourish. Add manure, leaf mold, or compost to your potting soil to ensure a consistent and adequate supply of nutrients.

Also, ensure that the soil is well-drained. To improve its drainage, take one part of the soil and mix it with one part of peat moss. Mix them properly and put back the soil mixture in the planting area. The planting container should have drainage holes at the bottom.

Another factor to consider before planting your tomato seedlings is the soil’s pH level. Use a testing kit to measure the soil pH. Ideally, it should be between 6 and 7. If it is below 6, add dolomite lime to raise it. If it is above 7, add granular sulfur to the soil to lower its pH.

4. Dig holes for planting the seedlings

Pots accommodate one tomato plant each, while grow bags, barrels, and crates can accommodate 2-3 tomato plants depending on the variety. Dig 2-inch-deep holes in the planting container. Allow 24 inches between plant bush tomato varieties and 16-48 inches between plant vining varieties

5. Plant the seedlings

The best time to transplant your tomato seedlings is 2-3 weeks after the last spring frost. At this time, the soil temperature is between 50 and 550 F, which is conducive for the tomato seedlings to grow. However, during other seasons, ensure you maintain room temperatures between 65 and 800 F.

Carefully, uproot the tomato seedling with a soil ball to protect its delicate roots. Use garden shears to cut off the lower sets of leaves on the stem and only leave the upper two sets. If the plant is taller than 6 inches, trim it down from the tip.

Set the roots in the hole in the new container. Ensure that the stem is buried up to just below the two sets of leaves. Burying part of the stem when transplanting makes the plant sturdier. It also enables it to grow a strong root system.

How To Grow Tomatoes Indoor: Taking Care Of The Plant

Tomato plant seedlings growing in pots on the windowsill
Source: Shutterstock

Watering

After transplanting, tomatoes require regular watering to establish their root system. Once again, the idea is to keep the soil moist but not overly wet. Avoid wetting the leaves and only water at the base of the stem. Ensure to water the soil deeply. You do not need to apply B-1 solution when watering to protect the plants against transplant shock.

Stem Support

The indeterminate varieties of tomatoes require a support system. Set up a trellis, cage, or stake soon after transplanting to avoid disturbing the root system when it has already developed.

Fertilization

Tomatoes require regular fertilization to encourage flowering and fruiting. Apply diluted fish emulsion every 3-4 weeks. Add compost manure midway through the tomatoes’ life cycle. If you notice blossom-end rot that is not a result of over-watering, apply a source of calcium like crushed eggshells.

Disease and Pest Control

Look out for early infestation of diseases and pests such as cutworms, aphids, whiteflies, tomato hornworms, and fruitworms. Take the necessary preventative action and control measures, such as avoiding injury to the plant, applying neem oil, and keeping the garden free of debris.

Pollinating

Tomatoes are self-pollinating, but you can assist them with the process by either gently shaking the stem of the plant daily during the blooming season or setting up a small oscillating fan nearby to mimic the wind.

Conclusion

Now that you know how to grow tomatoes indoors, you can enjoy a year-long supply of these fresh and flavorful fruits. There are many varieties of tomatoes you can grow indoors as long as you provide the appropriate conditions. Although you can start your own seeds, you can also buy seedlings from a local nursery and transplant them to your indoor tomato garden.

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I'm Jad, a biologist, blogger, and experienced indoor gardener. I am knowledgeable in plant biology, particularly in plant cultivation and propagation. I founded HerbsWithin.com in 2019 to share my knowledge in indoor gardening with passionate home growers.

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