You have started growing tomato seedlings with the hope of harvesting juicy tomatoes after some time. But the growth of your seedlings seems to be stunted and you wonder why.

Your tomato seedlings are not growing because of lack of the required sunlight and heat. They may not grow well because of lack of water or nutrients. The tomato seedlings may not grow because they are affected by pest or disease.

I’ve written down a lot more details that will help you figure out exactly what is going wrong with your tomato seedlings. And you can use the mentioned solution to get them growing well again.

1. Overwatering or underwatering

Tomato plants need a lot of water when growing foliage and fruit. So you may be putting a lot of water in the soil with the hope of growing strong seedlings.

The problem is that if your soil does not have good drainage, it will leave the area soggy. The plant roots will stay in this moist condition and develop fungal issues such as root rot.

The roots will start decaying and won’t be able to supply the required nutrients and moisture to the plant. And this will lead to stunted growth of your tomato seedlings.

You can prevent the problem of overwatering by checking the moisture in the soil before you pour water into it. Stick your finger a couple of inches into the soil and check if the soil sticks to it.

If the soil does stick, it means there is plenty of moisture and you don’t need to water. If your finger comes out dry, it’s time to water the soil.

The other end of this problem is underwatering where you’re neglecting your tomato seedlings and not giving them the required water.

The roots won’t be able to supply nutrients and moisture to the plant and it will start to dry out. The leaves will get wilted and lose color.

This is a less serious problem than overwatering but it will slow down the growth of the seedlings.

You can use the same solution here to check the moisture content of the soil every day as you inspect the seedlings. Stick your finger 1-2 inches into the soil and check if it feels moist.

If it feels dry, you need to water the soil well till the moisture can reach deep into the soil and to the roots of the tomato seedlings.

2. Lack of sunlight

Tomatoes are a warm-season plant, and they need full sunlight to grow their best. This means the seedlings should be getting at least 6-8 hours of sunlight every day.

If you’ve planted them in an area of your garden where there is a lack of sunlight due to obstructions like tall plants, walls, or fences, they will not grow well.

The tomato seedlings can’t produce the required food with photosynthesis that needs this sunlight.

If you’re in the planning stages of growing the plants, make sure to select a location in the garden that gets the required sunlight.

If you’ve already planted the tomato seedlings, you can dig them up and move them to a better location in the garden.

Another option is to try to remove the obstructions if that is possible. If tall plants or trees are growing and blocking the light, you can trim the branches off.

3. Lack of nutrients

Tomato plants can be heavy feeders where they need to get lots of nutrients from the soil. If you don’t have much organic, nutrient matter in your garden, the seedlings will be slow to grow.

The best solution is to a layer of organic compost in your garden soil. And to keep adding a little compost every month when the plant is growing.

If you don’t have compost, you can keep adding fertilizer so your tomato plants can continue growing well. You can consider using a balanced fertilizer or a nitrogen-rich fertilizer when the plant is growing foliage.

This could be a slow-release pellet fertilizer or a liquid fertilizer based on your choice. You mix the slow-release fertilizer into the soil and the nutrients are released when you water the soil. It’s best to keep adding the slow-release fertilizer every month when the tomato plant is growing.

organic fertilizer
Organic fertilizer I use for my plants

The other option is to use a liquid fertilizer that works faster than a slow-release one. You can mix this fertilizer in water and spray it on your tomato seedlings. You should do this once every couple of weeks to get the best results.

I recommend that you choose organic fertilizer rather than chemicals as they can be harmful to the plant, organisms in the soil, and wildlife. Also, follow the manufacturer’s instructions before using such fertilizer on your tomato plant.

4. Transplant shock

You may have started the tomato seedlings indoors or you may have purchased them from a local garden center. Now comes the time to transplant the seedlings to your garden outdoors.

If you plant them immediately, there is a good chance that the tomato plants will come under stress. This happens because the seedlings have been growing indoors and are not adapted to the outdoor conditions.

The stress will cause the tomato seedlings to lose health and this will show up as stunted growth in the plants. This problem is what we call transplant shock.

The solution to this problem is quite simple. You need to make sure the tomato seedlings get used to the outdoor conditions before you can plant them in the garden.

The easiest way to do this is to keep your tomato seedlings outside for a few hours every day and then bring them back in. You want to keep the seedling away from intense heat, wind, and rain.

You should keep doing this every day while increasing the time the seedlings stay outdoors. And after a week, the tomato seedlings will be ready to be transplanted to your outdoor garden.

5. Lack of required temperature

We already saw that tomatoes are a warm-season plant. This means that they prefer to grow in the warm temperatures of spring and summer.

If you try to grow the tomato seedling when the temperature is below 50 degrees Fahrenheit, the seedling won’t grow well.

You should grow the tomato seedling only when the temperature has gone above 65 degrees and the last frost date of your area has passed.

Sometimes the temperature may drop for a few days in your area. It’s best to protect the tomato seedlings using a row cover to keep the plants warm till the weather becomes warm again.

You can grow the tomato seedlings when the temperatures are low but you need to grow them indoors and provide them the required heat. You can do this by growing them near a warm place such as an oven. Or you can try using a heating mat to keep the soil and seedlings warm.

6. Pests

There is a chance that your tomato seedlings may come under the attack of pests. If there are a few pests, it won’t cause many issues and it’s a part of nature.

But if the infestation is large, they will start eating a lot of the plant and this will result in poor growth.

Some common pests that can attack the tomato plant are aphids, tomato hornworm, slugs, snails, whiteflies, and cutworms.

Pests like aphids and whiteflies may suck the sap out of the foliage and cause a lack of nutrients in the tomato plant. You can get rid of them by spraying water and dislodging them into the soil.

Ants farming aphids on my pepper plants
Ants farming aphids on my pepper plants

Slugs and snails will eat the foliage of the tomato plant and cause poor growth. You can pick them by hand at night and dispose of them. Or you can set up beer traps in your garden to get rid of them.

The tomato hornworm is a large caterpillar that likes to feed on the tomato seedlings. It’s best to pick these pests by hand and drop them in a bucket of soapy water.

Cutworms are pests that will eat up the stem of the tomato seedlings near the base of the plant. This will cause a drop in the supply of nutrients. And it may also cause the seedling to break.

The easiest way to protect your tomato seedlings from cutworms is to protect the base of the stem using a cutworm collar. You can make this collar using the toilet paper cardboard tube.

The best thing to do against pests is to keep an eye on your tomato seedlings every day. If you find any pest attacking the plant, you can take immediate action and get rid of the problem.

7. Diseases

Diseases can also mess up the tomato seedlings and stunt their growth. Some common diseases affecting a tomato plant are root rot, bacterial leaf-spot, and Fusarium wilt.

It’s best to monitor the tomato seedlings every day and find out such issues as early as possible so you can deal with them.

You can avoid fungal diseases by keeping the garden clean and avoid too much moisture on the plant. Water near the base of the plant and avoid splashing it on the foliage. Keep a good distance between plants and ensure there is good air circulation.

Root rot is a problem that occurs when the roots of the tomato seedlings are sitting in a lot of water. This may happen because you are overwatering the plant or the drainage is poor.

The fungal problem will cause the roots to turn black and soggy. They won’t be able to provide nutrients and moisture to the tomato plant. You need to take the plant out of the soil and trim the affected roots. Then plant it back in a different location.

Bacterial leaf-spot will cause dark spots on the leaves that will keep increasing. This will cause the leaves to turn yellow and fall off. You can try growing tomato seedlings that are resistant to this disease.

Fusarium wilt is a fungal disease that will cause the leaves to turn yellow or brown. It will also cause the stems to lose their color. The plant will eventually die due to this disease.

You can grow a variety of tomato that is resistant to Fusarium wilt. If the plant has been infected, you’ll need to cut off the diseased part of the plant. Or take the entire plant and dispose of it. Make sure not to grow tomato plants in the same area of the garden for several years.

8. Poor soil

Tomato plants need well-draining soil that retains enough moisture but drains out the excess. It should have a good texture that allows good airflow through the roots.

If the soil contains too much sand, the water will drain too fast and you risk drying out the roots. If the soil contains too much clay, it won’t drain water well and you risk drowning the roots. Both these conditions will cause poor growth of the tomato seedlings.

The best thing you can do is get a soil test done for your garden soil. You can do this with the help of your local extension service. Send them a few samples of the soil in your garden, and they will give you the details for a nominal fee.

The soil test results will also tell you what you need to add to the soil to improve it for growing the plants you want.

I recommend adding a few inches of compost to the soil. It will improve the soil texture as well as introduce beneficial organisms to the soil.

It’s great if you can make your own compost or you’ll need to purchase it from a local nursery or garden center.

9. Lack of space

Tomato plants need a lot of space so they can grow well without crowding each other out. This depends on the variety of tomato plants you’re growing. Vining varieties grow tall when you use a trellis or tomato cage while bush varieties can grow wide.

The lack of growing space would lead to competition for resources and slow down their growth. It will also restrict the airflow through the foliage causing humid conditions. This can attract fungal diseases to the tomato plant.

It’s best to keep spacing of 24-36 inches when you’re growing tomato seedlings next to each other. As they grow into large plants, they’ll have plenty of breathing space.

You can grow tomato seedlings close to each other when you begin growing them. But at some point, you’ll have to dig them out and plant them again so the space is suitable for each of them to grow well.

So if you have the space in your garden, start growing them with plenty of space in between. This will help save a lot of your time and effort later on.

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