Leggy Tomato Seedlings: Causes, Treatments, and Prevention

From start to finish, tomatoes are a delightfully easy plant to grow. However, if you’re new to growing tomatoes indoors, one of the common challenges is preventing leggy tomato seedlings. Now, starting tomato plants inside to extend the growing season is a great idea, but we should also be vigilant to keep our seedlings healthy and in ideal world stop them to grow leggy.

After you have sown our quality tomato seeds, and they have germinated in 5 – 14 days, you will have to think about how to give the seedlings the best start in life in order to have strong growing plants for the tomato growing season ahead so fixing leggy tomato seedlings is essential for a successful harvest.

As we go along on our seed-starting journey, we want to be able to recognise what a healthy plant looks like. Today let’s discuss what goes into growing strong tomato seedlings. This way we can get the most out of our plants and enjoy an abundant harvest.

Leggy Versus Healthy – What’s the Difference?

First things first, you’ll want to identify any issues your plants are having. If you’re new to growing tomato seedlings, it’s important to know what to look for. If you catch growth problems right away, before they get out of hand, you’ll have plenty of time to resolve the issue.

A healthy tomato seedling should have a somewhat thick and sturdy central stem that stands erect, with smaller offshoots of leaved branches. Fine hairs should also be present upon the main stem and branching sub-stems. The beginning of true leaves should be emerging abundantly.

Conversely, leggy seedlings have long, lanky, and narrow stems without true leaves. They may also appear hairless and look more like a vine. Such plants often fail to fruit or do so sparingly. Additionally, leggy tomato plants have a hard time supporting their own weight and are prone to breakage.

What Causes Leggy Tomato Seedlings?

In short, competition is the main reason tomato seedlings become leggy. If your tomato seedlings are competing for nutrients, space, or sunlight, they are likely to grow abnormally.

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Prevention is the Best Solution

Every gardener knows that growing plants can have some challenges. Even seasoned growers learn new things all the time. Therefore, if you have leggy tomato plants, don’t despair. We’re going to look at how to prevent this issue in the first place.

The best way to prevent leggy tomatoes is to fully understand the ideal growing conditions for tomato plants. Let’s briefly talk about the crucial elements that need to be present for healthy tomato plants.

Airflow and Room to Grow

Tomato plants need adequate airflow and plenty of space to grow. It’s always a good idea to space them for optimal air circulation and light exposure. Additionally, when seedlings have plenty of “elbow room,” they tend to grow out in a more lateral direction. However, when tomato plants are packed too closely together, they go into survival mode, and try to outcompete each other by outgrowing their neighbours vertically.

As your tomato plants grow, you’ll also want to make sure their roots have plenty of room to expand and grow. Ideally, a tomato’s tap root can go down quite far. Ergo, try to pick deep planters for your seedlings. Also consider, the gentle breeze from an electric fan can do wonders. The airflow will also help their stems become thicker, stronger, and sturdier.

Full-Spectrum Light

The most common cause of leggy tomatoes is lack of adequate light. When tomato seedlings are started outside, they get to enjoy direct sunlight for much of the day. Therefore, we need to recreate these lighting conditions when starting our tomato seedlings inside. If we don’t give our tomato seedlings adequate light, they will become leggy. Essentially, they are stretching and reaching toward the light in a desperate attempt to survive.

This is where grow lights come in. Ideally, young tomato plants should be placed under full-spectrum grow lights for about 12 to 18 hours per day. As the tomato plants grow, you’ll need to raise the lights higher to accommodate and make room for their reaching branches. Of course, on warm days, you can place your plant trays outside while temperatures remain warm.

Nutrients and Fertilising

Once your tomato seeds have sprouted, they’ll be hungry, and you’ll want to start thinking about what to feed them. There are a variety of fertiliser products on the market that you can buy for your small tomato plants. Diluted liquid fertilisers are often the easiest to use, at this stage use a general fertiliser and not a specific tomato one, as they are low in nitrogen. Though quite smelly, properly diluted fish emulsion is also a great source of nutrients for tomato plants. They love the stuff.

See also  How to grow tomatoes from seed


Soft, moist soil, rich with organic matter, is ideal for tomato plants. Soil that is too rich in nitrogen or too low in nutrients may cause problems for your tomato plants as well. Be sure to use a seed starter soil mix when planting your tomato seeds. Then, when you need to repot your seedlings, use a well-draining soil optimised for tomatoes.


Tomato seedlings like to live in warm daytime temperatures ideally ranging from 21° to 27° C (70° to 80° F). Sustained temperatures over 29° C (85° F) can start to strain your young plants. If temperatures reach upwards of 32° to 35° C (90° – 95° F), the seedlings may stop growing. For this reason, it’s important to remove heating pads and tray domes once your seeds have sprouted. Once your tomato sprouts are above the soil and leaves are branching out, only use your grow lights.

Try to keep nighttime temperatures somewhat low. A range of 15° to 18° C (60° – 65° F) is perfect. If you keep temperatures too high at night, your plants may think that it is daytime and that they are still submerged in soil. As such, they may then attempt to stretch toward the light. Let your seedlings have about 9 hours of darkness accompanied by cooler temperatures. Even better, you can use a thermometer to measure the soil temperature and get a precise reading.


Water your tomato seedlings regularly to keep their soil lightly moist. The soil shouldn’t remain soggy and needs good drainage. Similarly, it should never be allowed to become completely bone dry. A happy balance somewhere in between is the goal. Also, it’s best to water your tomato plants from the base so as to avoid getting water on their foliage.

Treating Leggy Tomatoes

Are your tomato seedlings leggy? Not to worry! After recognising that our seedlings are a bit tall and lanky, we can now commence with treating the problem. Simply follow the steps outlined below, and after about 16 days, you’ll notice a big difference in the health and quality of your tomato seedlings.

Repot the seedlings

Prepare a new container for each of your leggy tomato seedlings. Use one that is quite a bit deeper and wider than the original starter container. Then, gently dig up each leggy tomato seedling from its original container and replant it within the bigger container. As you establish the seedling in its new home, you’ll want to bury it deeply, up to its first set of (sprout) leaves, so that the length of the stem is covered in soil. Leaves toward the top of the stem should be left intact.

See also  Tomato Plant Care

Use a saucer to water

Water the seedlings from the base of the pot. In other words, place your seedling containers in a shallow tray and add water to the tray. This will encourage the seedling’s roots to grow and expand down toward the source of water. As the roots expand and grow, the tomato seedlings will become stronger. Additionally, the leggy part of the stem that is buried in the soil, will now start to grow roots too. This will, over time, add stability to the plant.

Provide more light

Lastly, you’ll want to fix the issue that caused your tomato seedlings to become leggy to begin with. Lack of light is usually the most common reason. If you already have a lighting system installed, perhaps move your seedlings closer to the lights or increase the number of lights to get full coverage for all of your plants.


Leggy tomato seedlings are a common problem that often occur when growing plants indoors. The temptation for some may be to give up or throw them out. Not to fret though, if you find that you have leggy seedlings, fixing these tomato plants is relatively straightforward.

Hopefully, we’ve helped you gain the confidence needed to give your seedlings another chance, and you can save them even if they are leggy. Simply follow the instructions we’ve outlined above. Also, remember that with each new season, growing your own tomato plants will become easier. You’ll continually learn new strategies and gain valuable experience too.

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