Why Are My Tomatoes Small?


There is nothing more frustrating than getting small tomatoes from your garden, especially after putting in lots of work to care for your plants during the season.  If you’re facing the problem of small tomatoes, you might be wondering what causes it to happen.

So, why are your tomatoes so small?  Your tomatoes will grow small with improper conditions, such as:

  • lack of water
  • high temperatures
  • lack of sunlight
  • lack of pollination

Your plants could also be suffering from root damage that occurred during transplant.  If your seeds or plants were mislabeled, then you may end up with smaller fruit than you were expecting (for example, cherry or grape tomatoes instead of beefsteak tomatoes).

Of course, many of these causes of small tomatoes are preventable, once you know what to do and when.  Let’s get into a little more detail on these causes of small tomatoes, and then we’ll talk about steps you can take to avoid small tomatoes.

Why Are My Tomatoes Small?

There are many possible reasons that your tomatoes are small, but the most likely problem is an environmental one.

For more information, check out this article from the Mississippi State University Extension on common tomato problems.

tomato plant with fruit
If you want bigger tomatoes, you will have to take steps to avoid some of the problems that cause small tomatoes.

Lack of water, high temperatures, lack of sunlight, or lack of pollination can all cause small tomatoes on your plants.  However, root damage or even mislabeled plants can cause smaller tomatoes than you were expecting.

Let’s start by taking a closer look at one of the more common problems that can cause small tomatoes: a lack of water.

Your Tomatoes Are Small Due to Lack of Water

Without enough water, your tomato plants will not be able to produce enough energy from photosynthesis.  This lack of both energy and water prevents your plants from producing larger fruit.

A lack of water could be caused by improper water timing.  Not only do you need to provide enough water, but you need to do it on the right schedule.

garden hose
Not only should you make sure you tomatoes get enough water, but you should pay attention to when and how they get water.

First, water in the early morning if possible.  This gives the water a chance to soak into the soil before being evaporated by the sun and heat of the day.

Do not water at night – even though it is cooler, you do not want the leaves of your plants to stay wet all night (this increases the chance of diseases).

Also, you are better off giving tomato plants deeper, less frequent waterings.  This encourages them to develop a stronger root system, which increases their resistance to drought when it really counts.

The water should be going into the soil to a depth of more than 2 inches each time you water (check with your fingers or a trowel).

For more information, check out this article on growing tomatoes from the University of Minnesota Extension.

If you have a problem with dry soil, then optimal watering alone may not prevent a lack of water in your tomato plants.

To help keep the soil moist, add some compost to your garden before the growing season.  This will help sandy soil to hold more water.

For more information, check out my article on making your own compost.

Once the growing season begins, you can spread mulch over the top of your soil to help prevent evaporation of water and to insulate against summer heat.  Speaking of summer heat, let’s get into our next cause of small tomatoes: high temperatures.

mulch
Mulch can help to retain moisture in soil and insulate against summer heat.

Your Tomatoes Are Small Due to High Temperatures

When temperatures get too high in dry weather, a lack of water often follows, which we already covered.  However, high temperatures can cause small tomatoes even when there is plenty of water for your plants.

According to Colorado State University, tomato fruit size will not increase in temperatures over 95 degrees Fahrenheit (35 degrees Celsius).

Tomatoes grow best when daytime temperatures are 65 to 85 degrees Fahrenheit (18.3 to 29.4 degrees Celsius) during the day and below 75 degrees Fahrenheit (23.9 degrees Celsius) at night.

High temperatures can also delay flower and fruit set on tomato plants, especially if pollination is a problem (more on this later).  Delayed flowering and fruiting can mean tomato plants don’t have enough energy or time to produce fruit as large as you were expecting.

There is not much you can do to change high temperatures.  However, there are a few things you can do to combat the effects of high temperatures on your tomato plants, including:

  • keep your plants watered
  • provide mulch to retain water and insulate against the heat
  • give your plants some shade, for example, by growing plants under a pergola or other shade structure.  For more information, check out my article on pergolas.

Of course, temperatures on the opposite end of the spectrum could be a problem as well.  As the growing season progresses, cold temperatures become less common.  However, don’t forget that cold nights early in the season can damage plants and cause small fruit later on.

For more information, check out my article on how to protect tomato plants from cold and frost.

Your Tomatoes Are Small Due to Lack of Sunlight

A lack of sunlight can also cause a lack of photosynthesis in plants, which leads to less available energy for growing fruit.  According to the Ohio State University Extension, tomatoes prefer full sun, which means that they need at least 6 to 8 hours of sunlight per day.

sunlight through forest
Tomatoes need full sun, meaning at least 6 to 8 hours of sunlight per day.

The best way to avoid this problem is to plant your tomatoes in a spot where there is plenty of sunlight throughout the growing season.  Remember that a spot that looks sunny in early spring may be totally shaded by tree leaves later in the season.

If you already planted your tomatoes, then consider removing some branches that are shading your garden.  In the future, avoid planting near tree lines or buildings such as sheds, garages, or your house.

Your Tomatoes Are Small Due to Lack of Pollination

Another possible cause of small fruit on tomato plants is a lack of pollination.  According to the Mississippi State University Extension, you can tell you have poor pollination when you look inside fruits and see a low seed count.

Poor pollination can occur for at least a couple of reasons.  One reason is extreme humidity levels.

Tomato plants are self-pollinating, meaning that they contain both male and female parts in the same flower.  To get fruit, the male part of the flower must release pollen onto the female part of the flower.

When humidity is too high, the male part of the flower has trouble releasing the pollen, since the air is too sticky.  When humidity is too low, the pollen has trouble sticking to the female part of the flower, since the air is not sticky enough.

Another possible reason for poor pollination of tomato plants is a lack of activity by pollinators, such as bees.  Extreme temperatures can prevent bees from doing their work of pollination.

bee on blueberry flower
A lack of pollinators, such as bees, can prevent proper pollination of your tomato plant flowers.

If you or nearby neighbors use pesticides, then that can also disrupt the activity of pollinators.  To prevent this problem, avoid using pesticides, and ask your neighbors to do the same.  Also, plant some plants that flower at different times to attract bees and keep them in your yard.

For more information, check out my article on attracting bees to your garden.

Unfortunately, there is not much you can do about extreme humidity, and a lack of pollinators may not be something you can fix right away.  Luckily, there is a way to pollinate your tomato plant flowers yourself.

Using an electric toothbrush, you can touch each flower to simulate the buzzing of bees and other pollinators.  This should stimulate the male part of the flower to release its pollen.

electric toothbrush
An electric toothbrush can help to pollinate tomato flowers in the absence of bees.

As mentioned above, high humidity can be a problem, so try to do this hand pollination when it is not too humid (or too dry).

For more information, check out my article on how to hand-pollinate tomato plants.

Your Tomatoes Are Small Due to Root Damage

If the roots of your tomato plant get damaged, the fruit (and the plant itself) can end up smaller than you were expecting.

tomato plant roots
The roots of tomato plants can be damaged when you transplant them into the garden.

Roots are sometimes damaged by stakes or cages inserted into the ground near tomato plants.  To avoid this, put in stakes and cages before transplanting your tomatoes outside.

Roots can also be damaged during transplant, especially if the tomato seedling becomes root bound in its container while growing.

One more thing to remember: do not put your tomato seedling in the ground with the pot it came in!  The plant may not be able to break through the pot to get to the surrounding soil.  If this happens, the plant will have trouble growing and producing large fruit.

Your Tomatoes Are Small Due To Over Fertilizing

You can also cause small tomatoes by over fertilizing your tomato plants.  For example, too much nitrogen can cause excessive green growth instead of flowers and fruit (think tall tomato plants with thick stems and branches and lots of leaves, but few flowers or small fruit).

fertilizer burn on leaf
Too much nitrogen can cause small tomatoes. Excessive salts in fertilizer can even burn a plant and its leaves, as shown here.

To avoid this, choose a low-nitrogen fertilizer, which will also help to avoid burning your plants with excess salts (found in some fertilizers).

For more information, check out my article on over fertilizing your plants, and my article on low nitrogen fertilizers.

Your Tomatoes Are Small Due to Mislabeled Plants

It seems unlikely, but it is possible that the seeds or plants you received were mislabeled.  If you grew cherry or grape tomatoes instead of a beefsteak variety, then you will get much smaller fruit than you were expecting.

This mislabeling may not be the fault of the seller – it could happen if a customer accidentally switched the labels at a garden center.

Your Tomatoes Are Small Due To Pests or Diseases

Finally, it is possible that pests or diseases are weakening your tomato plant and causing small fruit.  However, you would likely see other symptoms, such as stunted plant growth or distorted appearance, if this were the case.

Conclusion

By now, you have a much better idea of what is causing small tomatoes in your garden.  You also know how to prevent many of the most common problems that cause small tomatoes.

I hope you found this article helpful – if so, please share it with someone who can use the information.  If you have any questions about small tomatoes, please leave a comment below.

jonathon.david.madore

Hi, I'm Jonathon. I’m the gardening guy (not guru!) who is encouraging everyone to spend more time in the garden. I try to help solve common gardening problems so that you can get the best harvest every year!

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