Horticulture Magazine

Top Reasons Your Tomato Flowers Are Not Setting Fruit

yellow flowers of tomato plant

There are a number of reasons why tomatoes may not set fruit successfully.

In this article, we will discuss some of the most common reasons, so you can troubleshoot the problem and may be able to avoid encountering this issue in future.

The top reasons your tomato flowers are not setting fruit fall into two categories.

The first category is environmental factors out of your control. These might include the weather conditions – extreme temperature changes.

The second is due to environmental factors which are in your control (a mistake you may have made as a gardener).

Fortunately, the second category is more common in UK gardens. So there is likely to be something you can do to avoid seeing this problem again next year.

Read on to identify the most likely reason in your garden:

Blossom Drop: Flowers Drop Off Before Pollination Can Occur

three yellow flowers on tomato plant
Yellow flowers of tomato plant

One reason that your tomato flowers are not setting fruit can be that they drop off before they are pollinated. This is a sign of plant stress, and it can have a number of causes. The most common are:

  • Temperature fluctuations (especially sudden cold snaps with chilly nights).
  • A lack of water.
  • A nutrient imbalance.
  • Insect damage.

One common cause is that the nighttime temperatures fell too low during the time when the tomato plant was flowering.

Tomato plants need temperatures of around 10-23 degrees at night in order to retain their flowers.

If nighttime temperatures have dropped too low, this may have led the flowers to drop off before pollination could occur.

A sudden cold snap might be to blame, and the weather and your climate is, of course, a factor that is outwith your control. However, you could look out for cold snaps in future and take steps to protect plants when a cold night is forecast.

You could also plant out your tomatoes a little later to be on the safe side. Or consider growing tomatoes undercover in a greenhouse or polytunnel.

If sudden temperature changes are not to blame, the flowers may have dropped off before pollination could occur because you did not provide your plants with enough water.

They may also have dropped off because there was a nutrient imbalance. Remember, all plants need nitrogen, phosphorus and potassium, as well as a range of micro-nutrients. Too little nitrogen, or too little potassium, can both cause flowers to drop off.

Too much nitrogen can also be a problem. If you add too much nitrogen, especially in the form of synthetic fertilisers, the plant may focus on foliage growth at the expense of flowers and fruits.

Rarely, insects may have damaged the flowers and caused them to fall before pollination could take place. So keep your eyes peeled and be on the lookout for pests in your garden.

Not Setting Fruit: Poor Pollination

Bumblebee pollinating a yellow tomato flower
Bumblebee pollination

Another reason that flowers can drop off rather than setting fruit is that pollination did not take place, or there was poor pollination.

Tomatoes are typically wind-pollinated and are also sometimes pollinated by bees and other insects. Ensuring good fruit set involves making sure that there is good airflow and ventilation around the plants – especially those which are grown undercover.

Fruit set should be better if you always make sure that there are plenty of insect pollinators around.

If you are growing tomatoes undercover, then where poor pollination is a consistent problem, you can consider giving nature a helping hand by pollinating your tomato plants by hand.

You can vibrate open flowers from behind with a device like an electric toothbrush, and gently blow to release and disperse the pollen, or you can use a cotton bud to transfer collected pollen to the end of the flower stigma.

Easier techniques to improve results also include simply improving the airflow/ventilation where tomatoes are being grown. And ensuring that there are plenty of pollinators around through companion planting and generally making sure you have an insect-friendly garden.

Poor Fruit Set: Nutrient Imbalance

Blossom end rot in tomato fruits
Blossom end rot

If some flowers form fruits successfully, but fruit set is poor, then this, once again, may be a problem with nutrient imbalance. If you see only a few small and tasteless tomatoes forming on your tomato plants, this could be due to a lack of fertility.

There may also, again, be excessive nitrogen in the soil, or you may have fed plants with too nitrogen-rich a feed.

If there are some fruits forming, but fruit set is poor, and fruits do not develop properly (or drop off) this could also be a problem with a lack of potassium. Be sure to feed tomatoes with a potash rich feed (such as comfrey tea, for example) as the flowers and fruits begin to form.

Blossom end rot (brown patches on the base of fruits) could also denote a lack of calcium, or indicate that pH is low and the plant cannot absorb sufficient calcium from the soil.

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