Last Updated: May 10, 2023
So, your tomato seedlings are tall and spindly, flopping over in the gentlest breeze. You’re not alone! Leggy tomato seedlings are common, especially when grown from seed.
So, in this article, I’ll share my best tips to fix leggy tomato seedlings fast. With these methods, your plants will be back on track to growing sturdy and strong in no time.
What Causes Leggy Tomato Plants?
In most cases, leggy tomatoes are caused by low-light conditions. Whether your plants are in a window that doesn’t get much sun, or are under grow lights that are too high up, poor lighting causes tomato seedlings to stretch.
However, low-light isn’t the only cause of leggy plants. It can also happen from crowding your plants too close to one another. Tight spacing in greenhouses or on grow shelves often cause taller, more slender plants.
Lack of nutrients can also lead to thinner, spindly growth in tomato plants. If your seedlings were grown in a seed starter mix that does not contain fertilizer, this may be an issue.
While these are the main causes of leggy tomatoes, there is more than one way to fix the problem once it has happened.
How To Fix Leggy Tomato Seedlings
If you are unhappy with your leggy tomatoes and want to do something about it, you have options. Try any of these solutions to fix your leggy tomatoes fast!
1. Give them more light
Light I said, leggy seedlings are almost always caused by insufficient light. Tomatoes are sun-loving plants, so they need lots of light from day 1.
I use LED grow lights (I like this brand), which provide full-spectrum light. They are relatively affordable, last a long time, and are cheap on electricity. Once your seedlings sprout, turn on your grow lights.
Tomato plants should get around 15 hours of light per day, with 9 hours of darkness. This is much more light than a sunny window can provide, especially coming out of the short days of winter.
A sunny window will never perform as well as grow lights, but it can be enough for smaller home gardeners. If you use a window, just make sure it is the brightest one in your home (South-facing ideally). Also, anticipate that your seedlings will be a bit leggier, and that is okay.
2. Transplant them deeply
If your plants are just too tall and lanky, you can repot them into larger containers. This helps stabilize the leggy seedlings by surrounding some of the stem with soil.
I always recommend planting tomatoes deep (whenever you transplant them), burying the stem up to the first set of leaves. Doing this right away can help get your plants back on track to for healthy, strong stems while they are still young.
Once you repot your seedlings, water them well to encourage new roots to form. You can also place a stake in your pots to help support the weak seedlings.
3. Provide a gentle breeze
As soon as my tomato seeds sprout, I turn on a small fan to provide a gentle breeze. This not only improves air circulation, but it strengthens the small stems.
Over time, the seedlings will become stronger as they “resist” the breeze. This not only creates stronger seedlings, but it better prepares your plants for the natural winds outside.
I use a clip-on fan on our propagation shelf, keeping the fan turned on whenever the grow lights are on. Keep in mind that a breeze will cause the soil to dry out more quickly between watering.
4. Space plants out
Tomatoes grow quickly after sprouting, filling in a small growing area fast. So, if you have your seedlings in 6-cell trays, they may be planted too close together.
Spacing the plants out encourages more bushy, lateral growth rather than purely vertical growth. With less light reaching the sides of each individual plant, crowded tomato seedlings will stretch upwards towards the light that is available to them.
To solve this, do your best to space apart each individual plant. This may mean transplanting to create more space (see tip #2), or simply moving each tray a few inches from the next.
This same principle applies to other plants, too. If your pepper or cucumber seedlings are only a couple inches apart, the plants will elongate the main stem, making them appear leggy.
Keep in mind, this type of ‘legginess’ is less of an issue with tomatoes. You can simply plant them deep when it comes time to up-pot or move outdoors.
5. Fertilize (if necessary)
My last recommendation is to consider fertilizing your tomato seedlings. I like to use a seed starter mix for planting tomato seeds. It is the perfect media for germination, and is incredibly absorbent.
However, most seed starter mixed are nutrient-free. This means I have to fertilize the seedlings shortly after they sprout. If I don’t, the plants will become stunted or leggy.
In this case, I fertilize about 1 week after the tomatoes sprout. I like to use a water-soluble fertilizer with plenty of nitrogen to encourage leafy growth. I also dilute the fertilizer to about 1/2 the recommended strength.
Note: If you bought your tomato plants from the store, chances are they do not need fertilizer. Most nurseries use normal potting soil with plenty of nutrients added in.
Tips To Prevent Leggy Seedlings
Next season, you can prevent your tomato seedlings from becoming leggy in the first place! Here are my top tips for avoiding leggy plants:
- Light, light, light! Did I mention light? Tomatoes will grow faster, stronger, and more bushy when given enough light. My grow lights are set to be on for 15 hours per day, as soon as my tomatoes sprout.
- Transplant at the right time. As mentioned, tomatoes grow fast! After 2-3 weeks in plug trays, they are ready for repotting. Transplanting will naturally space out the plants, and planting them deep provides sturdier growth.
- Use potting mix for germination. If you don’t want to worry about fertilizing from a young age, just use normal potting mix to plant your tomato seeds. While it may be a bit chunkier, your tomato seeds should still germinate and grow normally.
Leggy tomato plants can be a big disheartening to see. But under ideal conditions, your tomatoes should grow strong and healthy from start to finish! Learn my full methods of growing tomatoes from seed here.