We grow tomato plants with the hope of getting delicious, large, juicy tomatoes from them. So it can be hard when you find that your tomatoes are not getting big enough.

Your tomatoes are not getting big because they are under stress. This can happen because of weather conditions like too much heat or cold. It could happen because the plant is not getting enough water. Getting too much or too little nutrients could also be the cause.

There are a lot more problems that can cause small tomatoes and I’ve listed them below. I’ve also written what you can do to solve this problem and help you grow larger tomatoes.

Extreme weather

Tomato plants grow well when the weather is between 65 to 75 degrees. If the temperature goes below this, the plant will get stressed and the growth of the tomatoes will be stunted.

The same problem will happen if the temperature goes too high such as 85 degrees or beyond. The high heat will stress the plant and it will try to protect itself by limiting growth.

You need to understand the growing season of your area when growing the tomato plant. You don’t want the weather to be too hot when the tomatoes are growing. You may be able to protect the tomatoes by using a row cover that shades the plant.

If you’re growing the tomatoes in a container, you can move it to a location that is having shade and a bit cooler.

You want to plant the tomatoes so they will grow in the spring/summer season and are ready for harvest before the first frost can hit them. Otherwise, the drop in temperature will cause stunted growth of the tomatoes and even damage the fruit.

If there is a sudden drop in the temperature for a few nights, you can protect the tomato plants with a row cover to keep them a bit warm.

Lack of water

Tomato plants need a good amount of water especially when they start growing tomatoes. If they don’t get the required water, the tomatoes will turn out small.

You need to make sure the soil always has the right moisture for the plant. The easiest way to know this is to inspect your soil every morning.

Stick your finger 1-2 inches in the soil and check if the soil sticks to the finger. If it does not, that’s an indication the soil is dry and you need to water it.

You can water it thoroughly till the water has reached deep into the soil. This helps keep the soil moist longer. It helps the roots grow deep into the soil which helps protect them from drought conditions and makes them strong.

You may not be able to water the tomato plant regularly if you travel often or if you forget. You can use drip irrigation or a soaker hose with a timer.

This method will help reduce the effort you need to water the tomato plants. And you won’t ever face the problem that there is a lack of water for them.

You should also use mulch in your garden near the plant. This is done by adding organic material like grass clippings, dried leaves, wood chips, or hay on the soil.

This layer of mulch will help reduce the evaporation of the moisture from the soil. It will help keep the moisture available for the plant longer.

Overwatering

Sometimes we get too enthusiastic and give a lot of water to our tomato plants. This can be an issue because it leads to overwatering.

If you keep watering the soil and don’t give it time to dry out, the moisture remains near the roots for too long. This creates a humid condition that can cause fungal issues such as root rot.

The roots start to decay and they are unable to supply the required nutrients and moisture to the tomato plant. This will cause the tomatoes to not grow to the required size.

Overwatering is a dangerous problem because you can’t see what’s going on in the soil. You see the plant is not growing well and think it’s due to a lack of water. So you keep watering which increases the problem.

My suggestion is to check the moisture in the soil before you think about watering the tomato plant. Stick your finger 1-2 inches in the soil and check if it comes out dry. That’s the only time you should think about giving a thorough watering to the soil.

If you suspect the tomato plant is suffering from root rot, you can dig near the plant and check the roots. If they appear to be dark, soggy, and smelly, that’s a sign of root rot.

You’ll need to dig out the entire plant and cut out the roots that have been infected. Then you need to transplant the plant to another location in your garden.

If all the roots of the plant have been infected, the plant won’t be able to recover and you need to dispose of it.

Lack of nutrients

Tomato plants are heavy feeders because they need a lot of energy to grow tomato fruits. If they don’t get the required nutrients, the tomatoes will not grow well.

I recommend that you add organic compost to your soil when preparing it in the garden. A few inches of compost will add lots of nutrients to the soil. It also adds beneficial microorganisms that keep improving the soil further.

If you can make your own compost that’s a good option. If not, you’ll need to buy some from a local nursery or garden center.

In addition to compost, it’s good to add fertilizer to your soil as well. I prefer to use organic fertilizer as those are not harmful to the wildlife and environment.

When you plant the tomato plant, you can use a balanced fertilizer having an N-P-K value of 5-5-5 or 10-10-10. This is balanced which means the nitrogen, phosphorus, and potassium are in equal measures.

You can even use a fertilizer that is higher in nitrogen when you start growing the tomato plant. The nitrogen encourages the growth of the foliage. You could use a fertilizer having an N-P-K of 10-5-5.

Once the plant has matured and starts growing blossoms, you should lower the supply of nitrogen. It’s better to start using a fertilizer that is higher in potassium as it will encourage flowers and fruit growth. You could use a fertilizer that is having an N-P-K of 0-5-5 or 0-5-10.

You mustn’t use a fertilizer that is high in nitrogen once the plant starts growing tomatoes. The excess nitrogen will encourage the plant to grow foliage rather than increase the size of the tomatoes.

Pests

Several types of pests can affect your tomato plant. If the infestation is less, there won’t be a problem.

But if the pests are eating and damaging the plant foliage, it will cause a drop in the nutrients the plant can get. This will reduce the size of the tomatoes on the plant.

Pests like aphids and whiteflies will suck the sap out of the tomato plant leaves. They may even leave black, sticky, residue known as honeydew on the leaves.

Pests like hornworms, caterpillars, slugs, snails, and beetles will chew on the leaves and cause stress to the plant.

Insects like cutworms will eat the stem of the tomato plant causing a lack of nutrients reaching the tomatoes and cause poor growth.

There might also be animals and birds like deer, rabbits, squirrels, crows, and robins that damage the plant. Either because they want the leaves or they are searching for food.

I recommend taking a good look at your tomato plant every morning as part of your routine check. This will help you find any signs of such pests as early as possible.

You can then find out what are the necessary actions you need to take to get rid of such pests from your tomato plant. This could be solutions like removing them by hand, spraying water on them, trapping them, or using pesticides if you choose to.

Diseases

Like pests, diseases are another problem that can affect your tomato plant. Some of them are cosmetic and won’t cause any issues other than making your plant look ugly.

But some of the diseases are bad and they will affect the foliage of your tomato plants causing the plant and fruit to become unhealthy.

The diseases that may affect a tomato plant include fungal, bacterial, or viral diseases. Some examples are leaf curl virus, blight, and verticillum wilt.

Fungal diseases are spread when a humid condition occurs near the foliage of the plant. You can prevent this problem by keeping water away from the foliage.

When watering the plant, make sure to water the base of the plant. Avoid splashing water on the foliage. You can do this well if you use a drip-irrigation or soaker hose.

It’s best to water the plant in the morning as the excess water on the foliage will evaporate when the sun comes out.

To protect your tomato plant from bacterial and viral diseases, you can try to find a variety that is resistant to them. This does not guarantee that these diseases won’t affect the plant but it does increase the possibility.

Once the plant has been infected by a disease, you can try to cut off the affected part of the plant. This may work for some diseases and the plant will grow back healthy.

But some of the diseases are internal and cannot be solved. You need to harvest as many tomatoes as you can before the plant will die.

Tomato variety

You can choose to grow from several different varieties of tomatoes. These may be determinate or indeterminate, vining or bush variety. They could grow large or small tomatoes.

So it could be just a simple misunderstanding that you picked a tomato variety having small fruits. Some varieties of small tomatoes include Tiny Tim, Baby Red Pear, Super Sweet, Yellow Currant, and Tumbling Tom.

If you want large tomatoes you should pick one from a variety like Beef Steak, Big Boy, Brandywine, Cherokee Purple, and Black Cherry.

You need to look at the information about the tomatoes when looking through a seed catalog and the seed packet. If you’re purchasing the seedlings, make sure to read the tags and understand what variety it is.

Lack of sunlight

Tomato plants are a warm-season plant that needs full-sunlight. This means at least 6-8 hours of sunlight every day. If they don’t get this required light, the plant will grow weak and develop small fruits.

The tomato plant uses sunlight to produce its own food and if the sunlight is poor, it can’t do that. This means a lack of nutrients for its fruit causing them to grow small.

If you’re growing tomato plants in your garden, make sure to plant their position before you plant them. The location in your garden should get the required amount of sunlight throughout the growing season.

Make sure it’s not planted near tall trees, walls, or fences that can hamper the sunlight the plant can get.

If the plant is already growing and not getting the required sunlight, you need to clear any obstacles. If there are tall plants or trees, you may be able to prune the branches and get sunlight.

If there is a permanent obstacle such as a wall or fence, you need to move the plant to another location in your garden that will get the required sunlight.

If you’re growing the tomato plant in a container, this is much easier to do as you just need to move the container to a suitable location.

Lack of growing space

The tomato plant you’re growing may be determinate or indeterminate. It could be a vine variety or a bush variety.

Depending on this type of plant, it will need space to grow tall and wide. If the plant does not get the required space, it will compete with other plants in the garden for nutrients. And that will not help the tomatoes to grow to their large size.

You should know the type and variety of tomato plant you’re growing. And provide it with the required growing space.

You may have started the seedling indoors or bought the transplant from a garden center or nursery. Read the seed packet or the seedling information to know how much area in the garden the mature plant will need.

If you have already planted the plant, you can consider moving it to another location. Or you can remove some of the other plants nearby so it can get the required space.

This is easier to do if you’re growing the plant in a container. You can just grow one plant per container making sure it’s large enough to hold the tomato plant you’re growing.

But if you’re growing the tomato plant in a container, the size of the tomatoes will be smaller than if you would grow it in the ground.

The plant growing in a container gets less space to spread its roots and get as many nutrients and moisture as it needs. The plant relies on you to provide these resources which cause sub-optimal growth.

Poor soil

Your tomato plant needs good soil that has the right balance of sand and clay. It has to be permeable so it retains enough moisture but drains out the excess.

If the soil contains too much clay, it will retain a lot of moisture causing the problem of overwatering that we have seen.

If the soil contains too much sand, the soil will dry out fast and you risk not giving the tomato plant the required moisture.

Both of these situations will cause poor growth of the tomato plants as well as the tomatoes on those plants.

If you are growing the tomato plant in-ground or in a raised bed, I suggest you add organic compost to the soil. This helps improve the texture of the soil and make it suitable for growing tomato plants.

You can conduct a soil test before starting to grow the tomato plants. Send a few samples of your garden soil to your local Extension Service.

They will give you all the details of your soil and the amendments you need to add to fix the soil and make it suitable for growing plants. They just charge a minimal fee for doing this.

If you’re already facing the problem, you won’t be able to change the existing soil. But you can take the plant out and replant it in a location that has good soil.

You can consider building a raised-bed with the correct type of soil and then transplanting the tomato plant in this raised-bed.

If you’re growing the tomato plant in a container, it’s important to use the right potting soil. Don’t try to use garden soil that is too heavy for such container gardening. It will compact in some time and cause drainage problems.

Lack of pruning

Tomato plants will grow a lot of suckers and branches especially if you’re growing a vining variety. If you don’t keep pruning the plant, they will keep growing.

If there are too many branches on the plant, there will be a lot of tomatoes growing as well. This is not a good thing because the plant has to spend nutrients and energy on all of them.

This spreads the plant thin and the tomatoes will be small as the plant can’t give the required nutrients to each of them.

It’s much more beneficial to prune the tomato plant and keep few branches as well as fruit on it. This will encourage the plant to focus on growing the few tomatoes on it. These will grow strong, healthy, and large.

You should prune the suckers that start growing between the leaves and branches of the tomato plant. When the suckers are less than 2 inches you can pluck them with your hand. If they are larger, you can cut them off with a bypass pruner.

You should also prune any yellow leaves and rotten tomatoes from the plant. Remove any small tomatoes that are not growing well. This encourages the plant to avoid spending energy on them.

If you’re growing the tomato vine on a support such as a trellis or a stake, you can also prune the top of the vine. You can do this when the top grows beyond the height of the support.