Tomato Seedling Problems and Their Solutions

So, you’ve got your tomato plant seedling. It’s germinated nicely, and you’re ready to plant it in a bigger pot, or even in the ground of your garden. Things are going along smoothly.

Unfortunately, disaster strikes, as you see that your seedling looks to be wilting or looking sickly!

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What could have caused this? How bad could it get? Can it spread to your other plants? Is it treatable?

So many questions, and so little time!

Seedlings are young plants, so it shouldn’t come as much of a surprise that they can suffer from some pretty gnarly problems at this early stage in their development.

Fortunately, we are here to help you figure out what said gnarly problems are, as well as the best way to treat them for your plant!

Yellowing Leaves

This will probably be one of the easiest things to spot on your tomato seedlings. The leaves on your little seedling are supposed to be a luscious, vibrant green.

So seeing them turn yellow, especially at such a young age, doesn’t bode well for their health!

There are probably two causes for your seedling’s leaves turning this color: Either, you are giving your seedling too many nutrients, or there is not enough magnesium in your soil.

How To Fix It

Fortunately, this might be one of the easiest problems to fix for yourself.

If it’s a case of over nourishing your seedling, make sure that they are in a pot or container with enough drainage, and lay off on the fertilizer for a little while. They shouldn’t need too much at this age, especially with a well-draining vessel.

If it’s a lack of magnesium, sprinkling a little Epsom salt into your soil will often do the trick.

‘Leggy’ Seedling Stem

At such a young age, it can be easy to assume that your seedlings are going to look spindly and quite thin. Tomato plant stems when they have just sprouted are quite thin after all!

However, if you notice your little plants looking particularly thin, or start to lean in a single direction, you may have what gardeners call ‘leggy’ seedlings.

This is particularly an issue if your plants are getting light from one direction. As plants that need light to photosynthesize, they’re going to try and face the direction where it is coming from!

How To Fix It

This is another easy fix that you can do yourself, with very little extra kit needed. Simply try and find a better spot where light can hit your plants from different directions, and the problem should fix itself.

Alternatively, if you’re using an artificial light source, keeping them closer to it may also solve the issue.

If it has gotten to the point where the entire plant is facing one direction, you can repot the plant, and bury the stem a little deeper into the soil to rectify the issue.

Drooping Seedlings

As we’ve already said, the leaves on a young tomato plant should be both a bright green, and look strong and plump in the light.

So, seeing leaves wilt and stem droop can feel like a real panic-inducing moment for gardeners!

The problem with this is simple, but can be a little frustrating to pinpoint exactly.

Either the tomato seedlings aren’t being watered enough, and the lack of nutrients causes the plant to droop, or there is too much water in the soil, causing the roots to rot or be unable to breathe, making the plant droop.

(Keep this fact in mind. These are the causes of a lot of problems for your seedling that we’ll cover!)

How To Fix It

While determining exactly which of these two problems is causing your seedling to droop can be tricky, the solution to both (and many of the other issues we’ll cover) is to have a regular watering schedule for your plants.

This will make sure that you’re monitoring the progress of your plant, while also making sure that you aren’t leaving it under-watered for several days, and overcompensating when you do remember.

Trust us, forgetting to water a plant, then overwatering it, might be the quickest way to kill any plant!

Black Lesions On Seedling Leaves

This can be a particularly troubling thing to see, especially on a small seedling.

Tomato plants are supposed to have uninterrupted, clean leaves. So seeing black spots and lesions would make any gardener worried. 

These lesions are usually caused by some kind of infection, usually fungal, and are called early blight. They create spots of necrotic tissue that can eat into the leaves and stem of a plant, causing it to wilt and eventually die.

How To Fix It

To fix this problem, you’re going to need a dedicated anti-fungal agent to deal with it.

Spray your plant thoroughly with a fungicide spray (including under the leaves too), and wait to see if the lesions state to shrink, fade, or stop spreading.

Add mulch to your soil to give your seedling some extra nutrients, and you should be fine. Bonide has a competent antifungal mix that you can use for this.

Leaves Turning Pale Green

Similar to how yellow leaves on a seedling are rarely a good thing, seeing pale green leaves where there should be bright green can leave some gardeners worried.

Like with the ‘leggy’ stems that we mentioned earlier, this can often come from a lack of direct sunlight or even a deficiency of nutrients in the soil.

How To Fix It

Luckily, this is a simple problem to solve. If it is a sunlight issue, making sure that your plant is getting anyway from 12 to 16 hours of sunlight (when possible) will often do the trick, helping return that chlorophyll to your seedlings.

If it is an issue of nutrition, repot your plant, and mix in some high-quality compost or mulch into the old soil, and your seedling should be healthy again in no time!

Seedlings Turning Purple

As we’ve said time and time again, your seedling should be a vibrant green color. So them turning purple is probably the last thing that you want them to do!

This one can be a little tricky to figure out and will depend largely on the type of tomato that you are growing.

Some tomato varieties do have spots or lines on the stem or undersides of their leaves. Meaning that this could simply be a natural point of their growth cycle.

That being said, this isn’t universal for all tomato cultivars. Some tomato leaves start going purple as a result of being overwatered or having a potassium deficiency in the soil.

Distinguishing between these two issues can be a real hassle, especially if you aren’t sure what kind of tomato you are growing!

How To Fix It

Firstly, try and determine what kind of tomato plant you’re growing. If the purple is just in spots currently, try and wait it out and see if the purple coloration spreads.

If you know that your tomato shouldn’t be going purple, and it’s spreading, repot the seedling, and add in some root and bloom mixture to the soil.

Slow Growth

Seedlings are often renowned for how quickly they grow and mature, especially tomato plants.

So seeing their growth slow down, while perhaps not an immediate cause for concern, might make some gardeners nervous for the health of their plants.

Generally speaking, plants have an optimal temperature where they germinate, sprout, and grow. Anything below that can cause said growth to slow down or stop altogether until the temperature warms up again.

How To Fix It

Again, this is a pretty simple solution. Just get your tomato plant back up to optimal heat!

The optimal temperature for a growing tomato seedling is between 21 and 26 degrees Celsius (or 70 to 79 degrees Fahrenheit).

Either place a heated mat at the previously-stated temperature underneath your seed tray or simply spray your seedling with warm water to help address this.

Make sure it isn’t too hot, or you may find yourself back at square one!

Black Mold On Stem

Now, if slow growth is a bad sign for your tomato seedling, then seeing black mold growing (see also: What Is The Black Beauty Eggplant, And How Do You Grow It?)on the stem almost feels like a death sentence! 

This is another fungal infection that you may be dealing with, damping off, often caused by having a seedling in soil that is too wet, too cold, and rich in nutrients, making it a breeding ground for other organisms like fungus.

How To Fix It

This issue will need a thorough solution, to avoid the Damping Off from coming back.

You’ll need to have a sterilized replacement pot ready, and fill it with a fresh new soil mix. Do not use any of the old soil that contained the damping off, as it may still contain spores or elements of the fungus.

Then you can place your seedling in the new pot

Leaves Turning White

Your leaves turning white, like many other colors, is not something you want in your tomato seedling! This could either be due to sun scalding (overexposure to the sun) or another fungal infection.

How To Fix It

Make sure that there is good circulation for your roots and soil, and repot if necessary. If the white leaves look to be spreading, cut off any parts that look affected.

Final Notes

So, there you have it!

As you can see, there are plenty of reasons why your tomato seedlings might start to look weak or sickly.

Many of them come from either over-watering, under-watering, or having soil that was contaminated with some kind of infection.

Keep your pots and trays sterile, stick to that watering schedule, and your little sprouting plant should be fine!

Amelia Haslehurt
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