How to keep indoor tomato plants from getting leggy?

Growing tomato plants indoors lets you savor their juicy, scrumptious fruit year-round, or simply get a jumpstart on the outdoor growing season by starting seedlings inside for transplanting when the weather warms up. No matter your ultimate goal, insufficient lighting results in leggy tomato plants.

• Place your tomato plants in a south-facing bay window, if possible. Tomato plants grown indoors need at least 12 hours of natural sunlight a day. A bay window provides light from the most directions and is ideal for indoor growing.
• Supplement natural sunlight with full-spectrum fluorescent lights if you do not have a south-facing window with at least 12 hours of sunlight. Providing more light per watt of electricity while emitting less heat, fluorescent lights are the most cost-effective and efficient lights for gardening indoors, according to the National Gardening Association. Provide 25 to 30 watts of light per square foot of full-grown tomato plants and 15 to 20 watts per square foot of seedlings. Place the lights 6 inches above plants or 2 to 3 inches above seedlings, and leave them on at least 16 hours a day.
• Reflect the maximum amount of light by placing your tomato plants in a white or light-colored room.

How to raise tomatoes from seed to seedlings?

Thousands of tomato (Solanum lycopersicum) varieties exist, and they can be categorized in several ways -- maturity class, fruit size, fruit color, use, and determinate or indeterminate. No matter the type, tomatoes need a sunny location and well-drained soil. Seed planting begins indoors 10 to 14 days before the last expected frost date. Starting seeds indoors then transplanting seedlings is one of the best methods for growing healthy tomatoes, because tomatoes require warm temperatures to grow and a controlled environment can be created indoors. Most varieties of tomatoes flourish in U.S. Department of Agriculture plant hardiness zones 2 to 10.

1. Fill a seed tray with clean, light potting soil. Sow a seed 1/4 inch deep in each cell of the tray. Put the tray in a room about 70 to 80 degrees Fahrenheit, and keep the soil evenly moist until germination.
2. Move seedlings to an area that has six to eight hours of sunshine per day or cool white fluorescent tubes 2 to 3 inches above them, lit for 14 to 16 hours per day. Keep the room temperature between 65 to 75 degrees Fahrenheit. Water consistently to keep the soil evenly moist, and feed the seedlings half strength soluble complete fertilizer every 10 to 15 days.
3. Prepare the garden bed when soil temperatures are above 60F and transplants have five to seven mature leaves, about six to eight weeks after planting. Spread 4 inches of well-composted organic mulch over the garden bed, and till it into the top 6 inches of soil with a garden fork or rototiller. Apply 4 to 6 cups of an all-purpose fertilizer such as 10-10-10 per 100 square feet, and mix it into the top 6 inches of the soil.
4. Harden off the seedlings 10 days before transplanting by gradually exposing them to an increasing number of hours of outdoor light and temperatures, until they can handle six hours of outdoor conditions daily.
5. Water the seedlings thoroughly a few hours and wait a few hours. Dig a hole that is about 2 inches deeper than the depth of the seedlings in the trays. Remove a seedling from the tray, handling it by the soil mass. Put the seedling in the hole.
6. Fill the hole with soil and tamp it down firmly to make a slight depression around the seedling. Space seedlings 24 to 36 inches apart and rows 4 to 5 feet apart, depending on the variety. Water the seedlings thoroughly.
7. Give the seedlings 1 to 2 inches of water per week. Side dress the seedlings with 1/2 tablespoon of nitrogen per plant four to eight weeks after transplanting.

Tips: Wooden stakes or wire cages may be installed for indeterminate tomatoes. A 3- to 4-inch layer of mulch such as compost will help maintain moisture and discourage weeds.

Tomato propagation with indoor soil

Propagating tomatoes is useful for growing a late-season crop, overwintering a favorite variety and indoor winter growing. Faster than growing from seed, propagation also results in a plant with the same qualities of the mother plant, which is particularly important when growing hybrid varieties. The proliferation of heirloom tomatoes benefits greatly from propagation, keeping those beloved but rare varieties producing for future generations. The use of indoor soil in propagation prevents pest problems, and provides a sterile growing environment for roots and consistent moisture control.

1. Remove a 6-inch cutting from a healthy stem of an existing tomato plant. Gently prune off all but the top two leaves. Look for a stem close to the ground; these will produce roots the fastest.
2. Place the stem in a vase with water up to 1 inch below the lowest leaf. White roots will appear in about one week. If the water becomes murky or slimy, replace with fresh water.
3. When the roots are about 1/2 inch long, the stem can be placed in indoor potting soil. Use a pencil to create a hole in the center of a 4-inch plant pot. Insert the tomato stem in the hole, and firm the soil around it. Water well after planting, and keep the soil consistently moist for the first two weeks.
4. Place the planter in a sunny window. Give it 1/2 cup of water when the soil is dry 1 inch below the surface. The plant is ready to transplant outdoors when it is 6 inches tall, or can be left indoors and replanted into larger containers as needed.

Plants should be given time to adapt before moving them outdoors full time. When they are 6 inches tall, move them outside for one hour the first day, two hours the second, adding one hour each day until the plant is outside all day. Remove all leaves but the top two, dig an 8- to 10-inch hole, and place the plant in the hole, covering all but the top two leaves. Water well.

Feed fruit-producing indoor tomato plants with 10-10-10 fertilizer once per month. Overwintering plants should not be fertilized until planted outside.

Strengthen a growing tomato plant to prepare it for the home garden

When you strengthen a growing tomato plant before setting outside in the garden, you have a much greater chance for healthy results.

Studies at Cornell University, the University of Georgia, and the University of Torino (Italy) show what tomato growers have known for years: motion helps tomatoes grow stronger, thicker stems. The studies used mechanical brushing to test and measure results.

Motion helps promote cell division and raised chlorophyll levels. Brushing plants helps them grow stronger, stockier (though shorter), and more able to withstand transplanting into the garden.

You can help strengthen a growing tomato plant by making it move! There are two ways you can give your tomatoes a workout: brush them and blow air on them.

Brushing tomato plants

• Begin brushing seedlings when they are 2-3 inches high. Pass your hand lightly over the seedlings several times a day.
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• When seedlings are 4 inches tall, push them a little harder. Grasp stems and bend them back and forth, being careful not to disturb their roots

Blowing on tomato plants

Get your tomatoes to move in the breeze. Aim a slow-blowing fan towards your seedlings 2 or 3 times a day, starting with 5 minutes at a time.

• Gradually increase breezes to 30 minutes a session.

A special note: wash your hands

Wash your hands before you brush them across tomato seedlings, especially if you’re a smoker. It is possible to transfer the tobacco mosaic virus through touch. Wash your hands after brushing, too. Some people are mildly allergic to tomato leaves and you may be one of them.

Re-potting tomato seedlings to a bigger container

A strong tomato plant gets that way from a strong root system. Re-potting tomato seedlings gives roots room to grow.

Your tomatoes will have the best chance possible to develop a healthy root system when you re-pot them at least once (sometimes two or three times) before setting them in the garden.

Frequently asked questions...

Q. When should I re-pot my tomato seedlings?
A. When your seedlings have 2 sets of leaves and the second set is at least ½” long.

The first set of leaves, called cotyledon (cot-uhl-EE-din) leaves (also referred to as false leaves or seed leaves) look like wings. They provide food for your new plant while it figures out how to grow some roots and work photosynthesis to its advantage.

The second set of leaves is often called “true leaves.” Be kind to them – they make chlorophyll. Soon, they’ll get the hang of food production. Then they’ll have full responsibility for feeding the plant, and the cotyledon leaves will shrivel up and say sayonara. When the first set of true leaves are about ½” long, you can re-pot.

Q. What size container should I use for re-potting my tomato seedlings?
A. A 4-6" container or transplant pot. You can always re-pot again to a bigger container if your seedlings get extra large or become root-bound. Make sure your containers have holes in the bottom for good drainage!

Q. What kind of potting mix should I use?
A. A good commercial or all-purpose potting mixture. Most potting mixes have a small amount of fertilizer which can be helpful to seedlings. Moisten the soil before repotting and make sure it’s not too tightly compacted when filling new containers.

Q. Should I thin my seedlings before transplanting?
A. Plant one seedling per transplant pot when re-potting. That may mean thinning extras. Use fork tines to separate tiny seedlings. If you’re careful, you may be able to repot both plants. You can also thin seedlings by snipping stems with a manicure scissors or using a tweezers to pull small plants, leaving the strongest and best-looking plants for re-potting.

Q. Can you give me some tips on the best way to do the actual re-potting?
A. Try these steps!

• Prepare your new containers by filling them 1/3 to 1/2 with moistened soil.
• With a spoon or your fingers, create a small hole in the center of the container about the size of the cell in which your seedling sprouted.
• Water the seedlings that are about to be transplanted.Use a spoon to carefully separate the seedling’s soil from the edges of the original pot. You can also loosen the roots from the container walls by squeezing and releasing the sides of the container.
• Scoop the entire soil plus root into the new pot. The spoon supports the weight of the seedling and soil from the bottom. Try to keep as many roots as possible intact.
• A big no-no: never grab the seedling by the stem or leaves to transplant it.
• Bury as much of the stem as possible, allowing leaves to bush out at bottom.
• Add moistened soil around the bottom set of leaves. Gently press soil around newly-potted plant.

Q. Should I fertilize re-potted tomato seedlings?
A. Sure, but don’t overdo it or you’ll burn the roots and lose the plants. Choose one of these feeding methods:

• Use a ¼ strength solution
• Fertilize with 1 teaspoon Miracle Gro Tomatoes per gallon of water or a mild fertilizer that’s high in phosphorus, which is known to boost root growth

Q. How important is good lighting?
A. Very. Give your re-potted seedlings 12-16 hours of light a day so they grow strong and healthy. Insufficient light can lead to leggy or stunted tomatoes – not a recipe for a robust start.

Q. How do I know if my tomato seedling needs to be potted a second time?
A. When it gets too big for the pot or gets root-bound, it’s time to move up to a bigger container. Make sure your pot is no bigger than one gallon.

Learn what tomato seedlings need after they germinate

When tomato seedlings pop through the soil, the whole game changes. It’s a lot like what happens when you bring a new baby home from the hospital. Your new sprouts require lots of TLC.

There are 4 secrets to grow tomatoes successfully:

• Light
• Water
• Air
• Nutrients

1. Light: let there be lots of it!

Bright light is super-important for healthy tomato seedlings! As soon as they sprout, they’ll reach up for sunbeams (or fluorescent beams). Seedlings need 12-18 hours of light each day. Do yourself a favor and give it to them. Otherwise they will become leggy and weak very quickly, which will set back production in your garden.

4 best ways to let there be light

1. Heated greenhouse. If your greenhouse is situated where it gets maximum exposure to sunlight, use it! Caution: out of sight is not out of mind. Your greenhouse may not be as accessible as your living room or kitchen, but make sure you check on your tomato seedlings every day. They can’t navigate this stage of development alone.

2. Cold frame. The best ones face south. Make sure yours has a tight-fitting lid so that heat stored up during the day from the sun will keep seedlings warm during cool nights. When the forecast is for below 20°F overnight, place an outdoor electric light inside the cold frame (one 60-watt bulb for every 12 cubic feet should be enough). During days when temperatures rise to 50° F and higher, prop open the cold frame lid. You’ll prevent baked tomato plants.

3. Fluorescent lights are among the most affordable and popular light source for seedlings. Mount lights with cords or link-type chains so you can adjust light height as seedlings grow. Keep lights 3-6” from tomato tops. Yep, that means you’ll have to check your seedlings daily and move lights up and down occasionally. Lights should remain on 12-16 hours a day. Turn lights off at night. (Seedlings need sleep, too.)

4. Sunny window. This is the most challenging lighting scenario for young tomatoes. Most home windows simply don’t have enough light for seedlings, especially in late winter and early spring. Choose a window facing south. Rotate tomato seedlings daily to prevent stem bending.

2. Water

Hydration in the tomato nursery can be tricky.

Water do’s and don’ts

• Do water your tomato seedlings enough so that you don’t let soil dry out or seedlings wilt.
• Do water from the bottom. (Remember … you poked holes in your containers, right?)
• Don’t over-water. Too much of a liquid diet fills in the air pockets in soil. When the roots can’t absorb all that water fast enough, they suffocate. Over-watering = drowning!

3. Air

• Take off plastic or clear covers from seedling containers to let seedlings breathe. Circulation will help prevent nasty diseases and fungi from spreading.
• Keep room temperature consistent, about 70°F. If your tomato seedlings are near a window, watch for drafts. Cold air mixed with over-wet soil is a deadly combo for seedlings. They’ll dampen off or develop nasty fungi faster than you can say “transplant time.”

4. Nutrients

The jury is still out among tomato gardeners about how much to fertilize seedlings at this point in their young lives. One side says plants are still feasting on the nutrients provided by their seeds. The other side says, “Give them some extra food! They need a strong start.”

On the other hand, mature tomato plants are like teenagers: you just can’t feed them enough. (Read more about fertilizing tomato plants in the garden and fertilizing tomatoes in containers.) Your seedlings aren’t quite at that point yet. It’s up to you during their tomato seedling babyhood to decide whether or not to feed them, and if so, how much.

A large number of successful home gardeners recommend waiting to fertilize until you transplant your baby tomato seedlings into their next-size-up containers. Others say to feed them right away.

Keep an eye out for yellowing leaves, which indicate the need for food. If possible, wait until your seedlings have at least 2-3 sets of leaves before feeding.

If you decide to give your plants some additional nutrients now, then feed seedlings with a weak (1/4 strength) water-soluble fertilizer like Miracle Gro Tomatoes. Keep an eagle eye out for crystallized salts on soil surface. That will tell you you’re feeding your seedlings too much.

How to plant tomato seeds?

When you plant seeds indoors in early spring, you will be ready to grow tomatoes for yourself as soon as the danger of frost is past and the soil is warmed.

And growing tomatoes for yourself is economical and fun!

Make sure that:

• You've calculated the best time for seed starting indoors in your area. 
• You've also picked a spot indoors where your seedlings can grow, selected containers, chosen potting mix, and moistened it.

The gloves are off! It’s time to plant seeds.

How to plant your tomato seeds

• Fill containers with moistened starter mix. (Reminder: seed cell trays work well for seed starting.) Make sure container bottoms have holes for drainage.
• Tamp soil down to remove air pockets.
• Use a pencil to poke a small hole in each cell or container.
• Plant seeds with a tweezers or pinch seeds between your fingers.
• Cover holes with pinches of extra moistened soil.
• Label planted seeds.
• Mist your planted seeds with a spray bottle filled with water.
• Keep records on planting dates and sprouting dates for different varieties.

Seed Starting FAQs (Frequenty Asked Questions)

Q. How deep should I plant seeds?
A. Some gardeners say 1/4". Some say 1/8”. A good rule of thumb for any seed is to plant it 4 times its diameter.

Q. How many seeds should I place in a hole?
A. Two, maybe three if you’re worried about germination rates. You can thin them out after germination.

Q. How many seeds should I plant?
A. Twice as many as the number of plants you think you’ll need to allow for thinning and non-germination. (And to have a few to give away to friends.)

Q. What kind of germination rate is normal?
A. Less than 100%. Federal standards require 75% germination rate for commercially-produced seeds. Most gardeners expect 80-90%. You can improve your germination rate when you pre-sprout seeds.

Q. When will my seeds sprout?
A. In 4-10 days, depending on variables like moisture, heat, and light.

Q. How can I improve germination?
A. Moisture and warmth work together. Don’t let the soil dry out! But don’t let it get soggy, either. Seeds need moisture to germinate. Keep containers covered to preserve moisture. Place containers in a loose clear plastic bag or under a clear plastic cover. Mist your seedlings when needed. Also, keep room temperature between 70-80° F. If it’s cooler, your seeds can germinate, but it may take a little longer.

Q. Should I fertilize my seeds or newly-sprouted seedlings?
A. Not yet. They feed on the food stored in the seed.

Q. When should I place my planted seeds under lights?
A. When they sprout.