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Why Are My Tomato Seedlings Curling? 5 Possible Reasons

Seeing curled leaves on a tomato plant is enough to scare any gardener, be it an experienced or beginner grower. The lucky news, though, is that curled leaves aren’t always a symptom of a serious problem. But that doesn’t mean that the issue isn’t worth investigating.

Why Are My Tomato Seedlings Curling
It is normal for the leaves to be curling like this? – via Reddit

Why Are My Tomato Seedlings Curling

So why are my tomato seedlings curling? A common cause of curled leaves on tomato seedlings is physiological leaf roll due to damp weather, cool weather, lack of water, excessive fertilizer, root damage, wind, dry air, hot air, pests, diseases, herbicides, wind damage, and more.

Let’s expound on all these reasons.

Pests

To get to the bottom of your seedlings’ curling issue, you’ll need to eliminate the possibility of a pest infestation that could be causing the issue. Pest cannot only cause viruses (more on this later), but they can also directly cause your tomato seedlings to start curly due to their feeding.

A great example is the microscopic plant pests known as broad mites, which are known to cause stunted growth as well as curling on plants. If not dealt with right away, broad mites eventually destroy the plants. Another point worth noting is that they love areas with low temperatures and high humidity.

With that in mind, if you inspect your tomato seedlings and find that they’re affected, you have no choice but to pull them out and get rid of them. However, do not compost the infected plants since the broad mites might survive in the compost pickles and re-infect your garden again in the future.

Herbicide Damage

When tomato seedlings are exposed to some herbicides, the typical symptoms they showcase include twisted growth and downward rolling of the leaves. In addition to that, the stems might split and start turning white, which will eventually cause the fruits to come out deformed.

Depending on how much your tomato seedlings have been exposed to the herbicides, the plant might or might not survive. Also, while the herbicide injury cannot be reversed, new growth might be normal if the plant isn’t killed.

Viral Infections

As pointed out earlier, pests have also been known to cause viral infections that can, in turn, cause curling in tomato seedlings. For instance, when whiteflies transmit the Tomato yellow leaf curl virus to your tomato seedlings, they will start becoming pale green in color and start curling.

In addition, this disease can cause the seedlings to start exhibiting purplish veins on their leaves’ undersides, yellowing of leaf edges, and even stunted growth.

Another viral infection you should be wary of is the Tomato mosaic virus, whose symptoms include rolling leaves, curling, tiny leaflets, and mottled leaves coloring.

With all that in mind, note that there isn’t a treatment for virus-infected plants. All you can do is remove and destroy the plant. Another point worth noting while at it is that weeds will often act as hosts to some of these viruses, so controlling their growth can minimize transmission chances.

Why Are My Tomato Seedlings Curling 2
Leaves curling on tomato seedlings. – via Reddit

Wind Damage

When strong winds strike your tomato garden, they can cause significant damage to your tomato seedlings in several different ways. For starters, the wind itself is sufficient to knock over the tallest seedlings if they’re not tied or staked properly.

The wind can also blow dirt and dust around at high speeds, which can, in turn, damage the plant’s leaves and cause them to begin curling as a result.

A third effect strong winds can have on your tomato seedlings is causing them to lose their water too fast, thanks to accelerated evaporation. In these cases, the seedlings will try curling upward in an attempt to minimize the water loss through evaporation.

So, to protect your tomato seedlings from strong winds, consider using cloches to cover them up.

This brings me to the next point.

Lack of Water

If a tomato seedling cannot supply all of its plant body with sufficient water, the seedling will usually start curling up. Expect this to happen even if the soil is still moist. In these cases, the plant is basically demanding more water than the roots can absorb or transport.

After extensive research, I learned that this problem is usually more likely in tomato seedlings that receive shallow or frequent watering. Both of these encourage shallow roots to develop on your seedlings.

So, to avoid shallow roots, water your seedlings infrequently and deeply. That should encourage deep, strong root systems that allow the seedlings to survive even through periods of relative drought. Note that insufficient water is also more likely in hanging or potted tomato plants.

Excessive Fertilizer

Tomato plants indeed need lots of nutrients to survive. Note, though, that too much is also harmful to the plants, particularly if you over-fertilize them using products rich in too much nitrogen. This usually tends to burn the plants’ roots, which eventually causes symptoms such as curling and root damage.

To avoid over-fertilizing your tomato seedlings, you’re advised to use a blend with lower NPK numbers written on the package. Furthermore, closely follow the instructions on the package and avoid adding too much fertilizer at the same time. Also, water the seedlings after applying the fertilizer.

Root Damage

Did you recently transplant your tomato seedlings? If yes, you probably damaged their roots, or the plants are going through some form of transplant shock. During transplant sessions, there are several reasons root damage can occur.

The first is the roots getting exposed to direct sunlight too long. This will usually happen when you place the seedlings on a tray as you dig holes for them.

The second way is rough handling of the roots during the transplant sessions, and the last one is accidentally pulling apart seedlings that were planted too close together.

When seedlings grow too close to each other, their roots get tangled, which significantly improves your chances of damaging the roots during transplant sessions.


Final Thoughts

I hope the detailed guide above has helped you ascertain exactly why your tomato seedlings are curling. Better yet, I hope the guide has helped you formulate a possible course of action as well, since that will take you a step closer to bountiful tomato harvests.