We’re obsessive tomato growers here at TGH, and try to grow enough to keep us fed right through summer and into early winter. That’s why we’re passionate to help you address any problems you might have with your tomatoes, from seed to harvest.

If your tomato plant looks healthy but no flowers are opening or forming along its vines, then you’re in the right place. We’ve got all the best tricks to grow thriving tomato plants, and help trigger tomato flowering within a couple of weeks.

In this article, we’ll look at the most common problems that cause tomatoes not to flower, as well as the best ways to fix them (spoiler: you can always fix it).

About tomato flowers

Tomato flowers are immediately identifiable by their acid-yellow petals set against an equal number of fluffy green sepals. As buds form on growing tips they look like fluffy green nodules and slowly expand to reveal soft yellow petals.

In healthy tomato plants, those sepals open and allow the petals to expand into a star-shaped flower with a long spiked cone. Without fully opened flowers, tomatoes cannot produce fruit.

Tomatoes need to flower fully in order to be pollinated as the cone at the center of their flower (the staminal cone) is actually the stamens glued together with nectar, meaning that pollination is only possible by bees, whose buzzing releases the pollen from the hidden anther that passes by the stigma before traveling back down to the ovary.

What triggers tomato plants to flower?

Tomatoes are triggered into flowering by age rather than sun or temperatures but can be stunted by improper conditions. When tomatoes have developed healthy trusses they will automatically begin flowering.

As we’ll discuss below, there are some things you can consider to boost flowering in tomatoes, as well as things to avoid that can stunt tomato flower production.

Why is your tomato plant not flowering?

Below, we’ve got the signs, reasons, and treatments for tomatoes not flowering so you can fix your tomato’s problems quickly and still get fruit this year. The top reasons that tomatoes fail to flower are:

  • Incorrect pruning
  • Pest Damage
  • Humidity
  • Lack of sunlight
  • Lack of nutrients
  • Time

1. Incorrect pruning

If your tomato plant looks healthy but no flowers are showing at all, there is one certain cause, but don’t worry, there are a few ways to fix it. The cause of healthy-looking tomato plants not flowering is almost always down to incorrect pruning.

Either by allowing side shoots to grow, or by leaving them, and cutting the horizontal trusses by mistake, you remove the flowering material or waste its energy. Side shoots are the diagonal shoots that come out between the main stems and the trusses.

If you’re new to pruning, we have some helpful resources for you:

2. Tomato flowers not opening

If your tomato flowers are showing but not opening, this is usually down to pest damage, infestation, or humidity. All three can cause the problem, but the symptoms will be different. 

Pest damage

If you notice strands of silk near the closed flower bud they could be covered in a substance called honeydew, which is secreted by spider mites and creates a sticky humid surface that glues the flowers together. You’ll notice tiny red or black arachnids on the underside of nearby leaves. 

The easiest way to fix this is to cut off the trusses, and allow side shoots to develop new trusses to replace them. It takes time, but within 1-2 weeks you should have new flowering trusses to replace the infested truss.

Humidity

Any humidity above average should be avoided for tomatoes as it encourages blight and other fungal problems. If you’ve got blight-resistant tomato varieties in your greenhouse, that doesn’t mean you can ignore the risk. Humidity can cause the cones in tomato flowers to seep nectar out to the rest of the flower. This can be fixed by simply rinsing the flowers gently and opening them by hand.

3. Lack of sunlight

Tomatoes are triggered into flowering by time rather than temperature or light conditions, and typically flower around 6-8 weeks after planting out depending on the variety. Even though tomatoes are reliable, in rare circumstances extreme shade and cold temperatures can stunt their growth enough to delay flowering.

If your tomatoes are in shade, move them somewhere sunny, keep them well watered and fed and they should quickly burst back into life.

4. Wrong nutrients

Tomatoes need some basic nutrients right through their lifetime, and any dedicated tomato fertilizer will provide balanced NPK ratios for everything beyond the seedling stage. 

If you’re trying more bespoke fertilizer tricks, like high nitrogen blood meal for young plants, and shifting to lower nitrogen after flowering, then consider switching to a straight tomato feed. Provided your soil is well maintained and there is a good balance of nitrogen and phosphorous in your feed there is no need to move between feeds at different stages.

To fix lower phosphorous (notable by a complete lack of flower buds) add a phosphorous plant food with added calcium like bone meal to the soil and water it through. Again, this isn’t an instant fix but provided it’s still early or mid-summer, there’s plenty of time for your tomato plants to respond to the amended nutrients.

5. Too late for tomatoes to flower

If your tomato plant is healthy, but just hasn’t flowered, you can usually trick it into flowering by bringing it indoors and keeping it in full, bright sunlight for a few weeks.

While tomatoes will always have flowered by the end of summer, albeit discretely in some cases, they want to produce fruit before they die back. This is a really common problem with store-bought tomato plants that have flowered before you buy them inside a shop and therefore fail to be pollinated properly.

Simply cut back trusses that have already flowered, move your tomato somewhere warmer, increase fertilizer slightly, and wait 2-3 weeks for new growth. This works on any indeterminate tomatoes which continue to grow upwards.

How to encourage tomato plants to flower

Tomato flowering requirements

There are a few basic things tomatoes need to flower at their best:

  • Regular watering
  • Correct fertilizer for the growth stage
  • Air circulation
  • Proper pruning

The importance of regular watering should never be underestimated with tomatoes, no matter what growth stage they are in. By regular watering, we mean watering the same amount at the same intervals.

As seedlings, irregular watering increases the chances of leggy plants, or worse still, damping off. As semi-mature tomato plants, irregular watering encourages side shoots and leggy growth, producing tall plants with fewer fruit-bearing trusses. As mature tomatoes, overwatering increases humidity, while under watering encourages pests, as well as splitting fruits that need regularity to expand evenly.

Once your tomato has started to develop flowering trusses, you can amend your fertiliser to include less nitrogen and more phosphorous, or calcium. Phosphorous and calcium support healthy flowers in the whole solanum family (potatoes, tomatoes, peppers and aubergines), while nitrogen makes the plant focus on foliage production.

If your tomato has begun showing flower buds but they aren’t opening, it could be down to poor air circulation, which can be helped by proper pruning and keeping greenhouse windows open for indoor tomatoes. High humidity can literally glue flowers together which will cause them to rot on the plant.

Indeterminate tomatoes flower more

There are two types of tomato plants; determinate and indeterminate. Indeterminate tomatoes are the vining type, which grows taller and taller until you cut off the top. Determinate tomatoes are pre-determined in their height, and the harvest you can get from them. 

If a determinate tomato plant has flowered it won’t flower again. If indeterminate tomatoes have had problems flowering, you can simply cut the un-pollinated trusses off which will trigger new growth and a fresh flush of flowers.

Proper pruning to get more tomato flowers

Do not prune bush-type tomatoes other than to remove excess foliage that can cause a build-up of humidity within the bush. For vine or cordon tomatoes, prune out any side shoots that grow from nodes. This reduces humidity, which helps flowering by creating a more open shape, and also helps your plants put energy into the flowering stems of tomato plants.

Conclusion

Tomatoes not flowering are usually an easy fix, especially since you have so many side shoots to save the day. But if you notice early tomato varieties failing to flower, you need to act fast. There’s always so much to learn when it comes to tomatoes, so keep practicing and you’ll get your fabulous harvest!

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