Why Won't My Tomatoes Fruit?

, written by Benedict Vanheems gb flag

Bumblebee buzz pollinating tomato flowers

Are your tomatoes flowering like crazy but refusing to fruit? Don’t worry – you’re not alone! Read on or watch our video to discover some of the most common reasons for tomatoes not fruiting…

Lack of Pollination

While other fruiting vegetables like squash produce separate male and female flowers, tomatoes have flowers with both male and female parts. This means they’re self-fertile and can pollinate themselves. However, you’ll get much more reliable fruit set if pollinating insects – especially bumblebees – enter the mix.

Bumblebees ‘buzz pollinate’, which means that their wings flap up and down at a frequency that creates their famous low, audible buzz. It’s this buzz that produces a vibration, so that when they visit a flower the pollen is shaken free from the male part to drift down onto the waiting female stigma. If you’re growing under cover, open up greenhouse or tunnel vents and doors to allow pollinators to access your crops. Encourage more pollinators into the area by planting nectar-rich flowers like marigolds among your tomatoes, and of course avoid using insecticides.

You can also improve fruit set by hand pollinating. You could go from flower to flower, transferring the pollen with a small artist’s paint brush, but a far more practical solution to dislodge the pollen to fertilise the female parts of the flower is to simply twang or tap on plant supports. You can even use an electric toothbrush gently on the back of the flowers to mimic a bumblebee’s buzz pollination!

Tomatoes have the potential to be incredibly productive

Extreme Heat

Many gardeners struggle with extreme summer heat – and so can our tomatoes! When it gets too hot pollen becomes sterile, especially if nighttime temperatures fail to drop below about 77ºF (25ºC).

All you can really do is hold out for temperatures to dip again. If your plants are under cover help them keep their cool by leaving windows, doors and vents wide open and perhaps adding blinds, cloth or greenhouse shading paint to filter out some of the sunshine.

Be sure to grow varieties suited to your climate too. If it’s particularly hot where you garden, seek out a warm-climate tomato variety that can better withstand your sultry summer.

Keep greenhouses well-ventilated to make sure pollen can travel to the female parts of the flowers

Humidity Too High or Too Low

If getting just the right temperature wasn’t enough to contend with, sometimes it can be a bit too humid or too dry for your tomatoes. The close, uncomfortable conditions that come with high humidity can make pollen so sticky that it clumps together and fails to drop onto the female stigma. Very dry conditions have the opposite effect: the flowers just aren’t moist enough for the pollen to properly stick, so it simply rolls off.

There isn’t much you can do about high levels of humidity other than ensure adequate ventilation and plenty of space between plants to help along airflow. Prune off some of the lower leaves to help air to circulate better too.

If bone-dry air is the issue, be sure to keep plants properly watered. As excess moisture evaporates it should help keep the humidity around your plants more stable. Ensuring enough water will also give plants the resources required to fully swell their fruits, while reducing the risk of them simply dropping off. If you’re growing under cover, splashing water onto paving – known as ‘damping down’ – will also help increase humidity.

In most area, tomatoes fruit much better given plenty of sunlight

Not Enough Light

If your tomato plants have lots of lush foliage but few flowers then consider light levels. Tomatoes love a sunny spot and will only do their thing if they receive a minimum of six hours of direct sunshine a day. Dull weather presents a temporary challenge, but if you’ve planted them in a less-than-sunny position you may be best moving your plants to somewhere brighter, because more sunlight means more energy to grow those fruits.

Choose a high-potassium fertiliser to encourage tomatoes to fruit

Insufficient Nutrition

Finally, check what you’re feeding your tomatoes. Once the first flowers appear you need to begin applying an organic fertiliser that is high in potassium (which promotes flowering and fruiting) and includes trace elements like magnesium for better all-round plant health.

A liquid tomato feed is ideal, and will help to grow healthier plants, reduce the risk of blossom end rot, and will increase the nutritional value of the fruits themselves. Most feeds are applied about once every two weeks by measuring out and diluting the concentrate according to the packet instructions, then watering it on at the base of the plants.

Don’t forget to aim for exemplary soil health by incorporating plenty of well-rotted organic matter into your soil at least once a year. This will build up a thriving community of soil life, which in turn will help to support all your plants, including those lovely tomatoes!

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"Excelent articles easily understood"
Anthony Topping on Tuesday 31 January 2023

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