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GROW TOMATOES INDOORS

Tomato Basics

Before you start growing indoors, learn the basics about type, temperature, and light. 
If the basics are doable for you, then follow the step-by-step directions that are further down the page.

Type

Tomatoes can be tricky, so stick with compact varieties like cherry and currant to make your growing more successful.

Temperature

Tomatoes needs a growing place above 70°F and away from cold, drafty windows. Temps between 75-85°F enable optimal fruiting.

Light

It's possible to grow a tiny tomato plant in a super-sunny window, but a grow light is generally necessary for decent fruiting.

Step-By-Step Directions

Step #1 Prep

Seeds

There are two terms to know before you choose your tomato seeds: Determinate and indeterminate. 

  • Determinate: More bush-like, with a set point where growth stops. You'll get some tomatoes before the set point, over about a 4 week period. When the growth cap arrives, it usually has a last heavy fruiting over a 2 week period and then stops producing. These varieties rarely need pruning and likely won't need staking if they're dwarf.  
  • Indeterminate: These varieties will grow as big as conditions allow (which indoors may enable growth of a really big plant). These plants must be pruned quite a bit and staked to control and support growth. Fruiting happens throughout the plants life.

Many indoor growers prefer indeterminate, but those are folks with the space for them. Both determinate and indeterminate are fine indoors, just pick whichever makes more sense for you. If you're new to gardening, you may actually want to choose a determinate variety as a good intro into tomato growing.

Below are some suggestions for small varieties. Just remember to check the seed pack to find out if it's a determinate or indeterminate variety. Also look for information about the mature size of the plant itself and the fruit. If you have a small space, then go for small on both. 

  • Good Varieties for Indoors:
    • Any "Cherry" varieties, Baxter's Early Bush, Terenzo, Silvery Fir Tree, Patio, Yellow Pear, Micro Tom, Tiny Tim, Ping Pong, Tommy Toe, Patio, Red Robin, Small Fry, Totem, Spoon/Currant Tomato, Kitchen
    • Colder-temp friendly (like a cooler basement): Siberian, Orange Pixie, Golden Nugget, Husky Gold

Soil

You'll need "Indoor Potting Soil/Mix" to start your indoor tomato plant. It's important to purchase an soil from a place that has kept the soil indoors as well. Indoor storage reduces the chance of bringing in unwanted house guests (aka bugs).

Note: If you like using "Seed Starting Mix," then feel free, but it's not necessary. I sometimes use it, mainly If you do use it, then first plant the seed in a tiny container/pot and then transplant the seedling into a new pot filled with moistened potting mix when you thin (step #7).

Container

Choose a breathable container like terracotta for your tomato plant. A 12" pot works for the small varieties listed above. Larger tomatoes will need larger pots... in fact, tomatoes love to spread their roots in the soil, so the bigger pot the better, particularly if you have an indeterminate tomato variety.

No matter the pot you choose, make sure it has drainage holes and you have a plate/saucer beneath it. 

Other

You'll need a grow light, spray bottle, watering can, sharp scissors, and fertilizer. More on those items below. 

Step #2 Plant

Fill 3/4 of your pot with moistened soil. Dig 1/4 inch holes for 2-3 seeds near the middle of your pot. Place a seed in each and cover with soil.

Optional Step: Cover your container with a see-through glass or plastic cover/wrap at this point to create a warmer and more humid environment for your seeds. This may speed up germination and reduce the need to mist the soil with water.

Covered or not, place in a non-drafty space above 75°F. Tomato seeds need moist soil and warmth to germinate. Light isn't necessary.

Step #3 Mist

Your fragile seeds don't want to be knocked around when they're trying to grow. To avoid disturbing them, use a spray bottle to mist them with water. 

Mist them daily to keep the soil moist. You may need to mist in the morning and night if the soil seems dry.

Don't have a spray bottle? Dribble water on the soil close to your seeds by dipping your fingers in a cup of water and shaking off the water over your pot.

Step #4 Wait

It takes some time for those little tomato seeds to erupt, usually 1-2 weeks. 

If you don't have a clear cover on them, mist the seeds and soil with water daily to keep the soil moist. If you have a cover on your seeds, peek in daily to make sure the soil is still moist.

Once your little plants erupt, remove any clear covering you may have had on them.

Troubleshoot: If no leaves appear after 2 weeks, consider starting a new pot. Check the dates of your seeds and soil to make sure they're still healthy. Consider putting your next pot of seeds on top of the fridge for some extra warmth (just don't forget they're up there!).

Step #5 Water

Tomatoes likes well-drained soil that is moist, but never soggy. The top of your soil should be dry, it's the moister below that is important. Watering is usually a daily or every-other-day activity, dependent on the plant, pot, and your growing environment. Don't worry though, it's easy to know if your tomato needs water:

Just stick your pointer finger in the soil when the top soil looks dry! Poke your finger into the soil until half your finger is buried. Is it still dry? Then you probably need to water.

Your plants will change their water needs as they grow, so this finger test can be handy (lol) as they start to drink more. Simply adjust your measuring tool for your own plants. For example, keeping the soil moist when only 1/4 or 1/3 or your finger is buried may be better for your unique plant. 

There are two main ways to water your plant: Top or bottom watering. You can also do a bit of both if you can't decide :)

Top Watering

Once your little plants erupt, you can switch to a watering can that has small holes or continue to mist the top of the soil around your plant. As your tomato plant get bigger, it'll be able to survive a douse of water (I'll dump unfinished glasses of water... sometimes a bit of stale coffee... in my plants). 

Bottom Watering

This appears to be the easiest time to switch to a bottom watering cycle for those who choose to go this watering route. Bottom watering just means placing water in the saucer/drip pan under the pot (rather than watering the soil from the top). The roots suck up the water through the soil. Bottom watering can help deter insects and help the plant grow even more stable and strong. That's a really good thing for top-heavy plants (like tomatoes or peppers). If bottom watering, it's also helpful to flush the plant monthly by top watering to soak. Dump out any water that flows into the saucer. Not sure about watering from the bottom quite yet? No worries! Water from the top.

How do I know if I am watering too much or too little?

Too much water: Lots of leaves and no fruit, cracked fruit, black/brown spot on bottom of fruit that spreads (blossom end rot), bumpy or blistered lower leaves. Later signs of overwatering include consistently wilted and discolored leaves and stems that later fall off. 

Too little water: Strangely, over watering or under watering creates similar effects on the plant leaves. Including: Wilted, discoloring, or dropping leaves. Burnt leaf tips may also appear.  

Remember: It's OK if you screw up with watering. As you learn more and get more connected with your plants (seriously!), you'll get better. And thankfully, most watering mistakes caught early can be fixed.

Step #6 Light

South or West-Facing Window

Apparently it's possible to get a tomato plant to fruit with windows only... I've never had success though. If you want to try, choose a teeny tomato plant (12" tall max) to improve your odds. Choose the absolute sunniest spot in your home (a South or West-facing window) and rotate your plant every few days for even exposure. 

Grow Lights

Learn more about grow lights from this GVI post. The short of it though: Use a balanced spectrum LED grow light for your tomatoes. You can add a red-spectrum dominant light during flowering and fruiting if you want to play with lights and try to boost production. You can also use a fluorescent grow light. See distance and timing for your lights below:

  • Standard Fluorescent: Keep this light about 3 inches from the top of your tomato and keep on tomato for 16-18 hours. 
  • Compact Fluorescent: Keep about 1 foot from the top of your tomato and keep on for 14-16 hours.
  • LED: Keep about 1-2 feet from top of tomato and keep on for 10-16 hours.

Rotate your plant every couple of days or so to get even light exposure. And because all lights are a bit different, you'll need to pay attention to your plants and adjust distance from plant and duration as needed. Signs to look for:

  • Too close: Leaves will get burned and look brown/yellow.
  • Too far or not enough light: Tall, weak-looking plants that are growing slow. 

Note: Plants have a biological clock and appreciate rest/dark periods, but most plants don't clearly suffer from too much light. So, the goal is to be efficient and use as little light as possible while still getting the best fruit production. See what suggestions your particular light says for your plants and go with the lower or mid-range duration. You can always bump up duration if you think your plants need more light.

Step #7 Thin

If you have more than one seedling, then you'll need to thin or move your plants. Do this when your seedlings are a few inches tall. The seedlings should also have 1 or 2 sets of leaves. 

Choose the best seedling and move it to the center of your pot. If you have more than one seedling that you want to keep, then move the other(s) to a separate pot. 

How to move seedlings(s): Dig enough dirt in the spot you want to put the seedling so that it will sit just as it was before you removed it. Use a spoon to scoop out the seedling(s) and gently move to the new spot. Replace any dirt as needed to secure the new seedling. Press down on the dirt all around the seedling to keep it in place. 

If you used seed starting mix and are moving your seedling from a tiny container, then try to simply flip the seedling into your palm. I usually place the seedling between my second and third finger, then flip the container into my palm. The seed starting mix will spill out, so do this over something that can catch it for later reuse. Shake off some of the seed starting mix from the roots of your seedling and then transplant into your pot with moistened soil.

Step #8 Fertilize

Tomatoes need nutrient rich soil to fruit. Adding organic fertilizer to your plants as early as two weeks after germination may be necessary, dependent on the soil you're using. Some potting soils claim their soil will provide sufficient nutrients for 3 or so months. Just check your bag to see when you may need to start fertilizing.

Try an organic, 5-10-10 plant-based fertilizer to support your tomatoes. Organic fertilizers are generally more simple to use (vs. a non-organic recipe) and are more forgiving of mistakes. Start with less and build up as needed. 

Once you start fertilizing, you'll need to continue every 2-4 weeks. Simply follow the directions on the label. 

Step #9 Prune

The amount of pruning that will help your plant is different dependent on your tomato variety.

Pruning a Determinate Indoor Tomato

You don't want to prune a determinate variety much at all. If you like, you can remove all suckers below the first cluster of flowers. If your plant is too full and you're worried about air flow, add a fan on low and prune a few suckers. Make sure the fan rotates and doesn't just blow constantly on your plant.

Pruning an Indeterminate Indoor Tomato

Indeterminate indoor tomatoes are wild creatures! A little pruning is usually helpful outdoors and a bit more pruning is nearly necessary indoors.   

Using the simple method below, you'll start the pruning process about 4-7 weeks after thinning your plant. 

Good thing to remember: Pruning is a science and art. It takes practice. Learn the basics and then trust your intuition as you get more comfortable and learn more about your plants and your indoor environment. Also: Prune conservatively... you can always prune more later.

The Simple Indoor Tomato Pruning Method below is a place to start. It controls your tomato to one or two stems. As you get more confident in your tomato styling ways, then you'll likely prune differently or try other methods that interest you.

Simple Indoor Tomato Pruning Method

  1. Look for the lower cluster of flowers/fruits on your plant. 
  2. Under that lowest cluster, you should see a big sucker (the growth coming between a leaf and the main stem- see image below). This sucker may be nearly as big as the main stem coming out of the soil.
  3. Keep that sucker directly under the cluster.
  4. Pinch or cut (with a sharp scissors/knife) any leaves below that sucker. 
  5. Pinch out any suckers above the lowest fruit/flower cluster.
  6. Continue to pinch out suckers throughout your tomatoes life. 

Step #10 Stake

Dependent on the type of tomato you have, you may need to stake it for support. Usually when it's about 1 foot tall. 

Small/dwarf, compact tomatoes often don't need a support. However, it can be helpful to put a support in, just in case. A stick, dowel, chopstick, or small bamboo stake will do the trick. Just place it a thumbprint or so away from the main stem and carefully push down. You can just leave it for future use or secure it now to the main stem with some twine, yarn, garden tape, or something else. Don't tie or tape it too tight as you'll need to leave space for the main stem to grow.

As your tomato grows, it may start to lean. Secure it to the stake if you haven't already and secure it again further up the stem as needed.

If you have an indeterminate or larger tomato variety, then you'll likely need a tomato cage of some sort to help control the growth up rather than sprawling across your floor. This will also help support the plant as fruits develop.

There are lots of tomato cage types or DIY options. There is no right or wrong, but some are better fits for the way you like to plant. For example, if you want to plant all your tomatoes in a row, then a trellis option may work well. The right support for you may also depend on how you want to prune your plant (see Step #10).

Personally, I like to trellis my tomatoes or use collapsible or flat bamboo tomato cages. Trellises and collapsible options are less cumbersome than the big wire cages, take up less storage space, and they look good (nice if you're growing tomatoes in your living room).

No matter the types, most cages will just fit right over your plant or sit on one side. As it grows, you can assist its upward growth by helping larger stems hang over the supports. You may also need to secure the plant in multiple places using garden tape or twine, yarn, or something else to keep it in place. Secure it gently, leaving room for growth. 

Step #11 Pollinate

Lol... don't worry, this is easy. Most tomato plants will self-pollinate, but indoors can be more difficult. All you need to do is give your tomatoes a little shake every week or so when you see flowers on the plant. Nothing wild, just hold onto the truss and give it a little wiggle.

Optional Fan: You can also utilize a fan in your growing space to assist with pollination and air flow. It's not necessary, but it's worth using if you have 5+ plants in one room and have a fan available. Let the fan blow on low for a few hours a day or so. 

Step #12 Harvest

Finally! Ripe tomatoes have arrived! Be sure to check your seed pack to know what "ripe" is for your particular variety.

When ripe, simply hold the stem that's attached to your tomato with one hand. With the other hand, twist the tomato off the stem.