How Does Tomato Blossom Set Spray Work? (Plus When To Use)

Maybe you have heard of tomato blossom set spray and are wondering how it works.  If you are having a tough year getting fruit on your tomato plants, then you are probably also wondering when and how to use it.

So, how does tomato blossom set spray work?  Tomato blossom set spray works by providing kinetin, which is a cytokinin hormone, to promote fruit production from the flowers on a tomato plant.  Tomato blossom set spray can also work on other common garden vegetables, including beans, cucumbers, eggplants, melons, okra, peppers, strawberries, and grapes.

Of course, there are some alternatives you can try before you go with tomato blossom set spray, which we’ll discuss.

First though, let’s get into how tomato blossom set spray works and when to use it.  Then, we’ll look at the alternative methods you can use to get fruit from the flowers on your tomato plants.

How Does Tomato Blossom Set Spray Work?

Tomato blossom set spray, or blossom set hormone, is a liquid that is sprayed on the flowers and leaves of tomato plants.  This liquid encourages tomato plants to produce fruit from their flowers.

tomato flowers
Tomato blossom set spray is a liquid sprayed onto the flowers and leaves of tomato plants to encourage them to set fruit.

Tomato blossom set spray causes tomato flowers to set fruit, even without proper pollination.  This occurs thanks to the natural plant hormone cytokinin (in the form of kinetin) in the blossom set spray liquid.

Kinetin is a class of plant hormone that promotes cell division.  For more information, check out this article on kinetin from Wikipedia.

Thanks to its kinetin content, tomato blossom set spray promotes flowering, increases blossom set, and increases fruit yield of tomato plants.  This is especially helpful when proper pollination is impossible due to lack of pollinators or extreme weather conditions.

There is one important thing to remember about fruit that grows due to the use of blossom set spray without proper pollination.  Although the fruit will form properly, the seeds will not.

So, if you have an heirloom tomato variety and you are hoping to save the seeds, you will need some fruit that develops as a result of natural pollination.  It may be a good idea to mark some of your tomato plants for seed saving and avoid using blossom set spray on them.

Also keep in mind that the use of blossom set spray is not limited to tomato plants.  It also works to promote flowers and fruit on beans, cucumbers, eggplants, melons, okra, peppers, strawberries, and grapes.

How to Use Tomato Blossom Set Spray

Before using tomato blossom set spray, plan ahead accordingly.  Check the weather, and make sure that no rain is in the forecast.  Otherwise, your tomato blossom set spray will wash away shortly after applying it – after all, you don’t want to waste it!

Shake the bottle well before applying the product.  Spray the flowers and nearby foliage until the leaves are completely wet.

Repeat the spraying procedure above as blossoms appear, or every 1 to 2 weeks.

heirloom tomato
Tomato blossom set spray can encourage fruit to appear, even when proper pollination does not occur.

For more information, check out the product label for tomato blossom set spray from Bonide.

When to Use Tomato Blossom Set Spray

You should use tomato blossom set spray when the blossoms first open on your tomato plants.  However, there are certain scenarios when it is especially helpful to use blossom set spray: cool temperatures, poor pollination, or indoor growing.

Remember that tomato blossom set spray will not fix cultural problems, such as improper watering, lack of nutrients in the soil, or insufficient sunlight for your plants.

Use Tomato Blossom Set Spray in Cool Temperatures

Normally, cool temperatures below 65 degrees Fahrenheit (18.3 degrees Celsius) during the day or 55 degrees Fahrenheit (12.8 degrees Celsius) at night will prevent tomato plants from setting fruit.

However, tomato blossom set spray can promote fruit set from tomato flowers even in cool weather.  This can be useful for encouraging your plants to start producing fruit if you planted too early in the season, or if the weather is unseasonably cool for a stretch of time.

Unfortunately, tomato blossom set spray will not prevent flower or fruit drop on tomato plants in extreme heat.

If daytime temperatures are above 95 degrees Fahrenheit (35 degrees Celsius), or if night time temperatures are over 75 degrees Fahrenheit (23.9 degrees Celsius), then tomatoes may stop setting fruit or drop their flowers.

For more information on fruit and blossom drop, check out this article on challenges in growing tomatoes from the Iowa State University Extension.

Use Tomato Blossom Set Spray for Poor Pollination

If your tomato plants are experiencing poor pollination, then tomato blossom set spray may be an option to consider.  One reason for poor pollination is lack of pollinator activity.

bee on blueberry flower
Poor pollination can occur due to a lack of bees and other pollinators – this can happen when too many pesticides are used nearby.

This can occur due to cold weather.  It can also happen if there is heavy pesticide use nearby.  If you or any of your neighbors are using pesticides or other chemicals (herbicides for lawn care, for example), then bees and other pollinators may die or move somewhere else to find cleaner air and water.

Poor pollination of tomato plants can also occur due to extreme humidity.  Both high and low humidity levels can prevent proper pollination.

To understand why, it is important to remember that tomato plant flowers are self-pollinating.  This means that the flowers contain both male and female parts.

Under ideal conditions, the male part releases pollen onto the female part, and the female part is fertilized and produces fruit.

For more information, check out my article on tomato plant pollination.

However, if humidity levels are too high, then the male part cannot release its pollen, since the air is too sticky with excess moisture.  This prevents proper pollination of tomato flowers.

Likewise, if humidity levels are too low, then the male part of the flower can release its pollen, but it will not stick to the female part of the flower (the air is too dry).  This also prevents proper pollination of tomato flowers.

No matter what the cause of poor pollination, blossom set spray can help your tomatoes to get started when pollinator or environmental conditions are not ideal.

Use Tomato Blossom Set Spray for Indoor Growing

Finally, tomato blossom set spray is also useful for indoor growing.  When growing indoors, you can control the temperature, light, water, and humidity fairly easily.

aeroponics towers
If you are growing plants indoors, then blossom set spray can help to produce fruit in the absence of bees and other pollinators.

However, there are not going to be any pollinators in your indoor setup.  So, you will have to find another way to pollinate your tomato plants.

One option is to use a toothbrush, tuning fork, or even your finger to cause a slight vibration on each tomato flower.  Often, this will be enough to cause pollination to occur.

However, you can also use tomato blossom set spray to encourage your flowers to start producing fruit.  This may be useful if you are keeping temperatures a little cooler to save energy, or by necessity in a greenhouse that is difficult to heat above a certain temperature.

When Do Tomato Plants Start Producing Fruit?

You may be wondering when to consider using tomato blossom set spray for your flowers, to ensure that you get a harvest this year.

Roma tomato plant
Most tomato plants will produce ripe fruit 7 to 14 weeks after transplanting into the garden (it can take 25 more days when planted from seed).

In general, tomato plants produce fruit 7 to 14 weeks (49 to 98 days) after transplant into the garden.  It takes 25 days longer (74 to 123 days) to get fruit when growing tomato plants from seed.

For more information, check out my article on when a tomato plant produces fruit.

Remember that cold temperatures can delay fruiting on tomato plants with flowers, sometimes by 10 to 14 days.

According to the University of Maryland Extension, “tomato flowers must be pollinated within approximately 2 days of becoming viable or they will abort” (eventually dropping off the plant).

With this in mind, you may want to start using tomato blossom set spray after trying other methods (such as encouraging bees and other pollinators and manual pollination by toothbrush or other means).

A tomato plant will only produce so many flowers, and you don’t want it to waste too much energy on producing flowers only to drop them.  If you have seen flowers drop off over a period of 2 to 3 weeks with no fruit appearing, then consider using your tomato blossom set spray.

There is one other thing to keep in mind: sometimes, you will get big tomato plants, but no flowers or fruit.  This can occur when there is too much nitrogen in the soil.

This excessive nitrogen encourages “green” growth on the plant, giving you a taller plant with thicker vines and branches.  However, this green growth comes at the expense of flowers and fruit.

For more information, check out this article on tomato growing challenges from the University of Arizona Extension.

If you suspect that you have the problem of too much nitrogen in your soil, try using a low-nitrogen fertilizer to encourage flowers and fruit on your tomato plant.

For more information, check out my article on low-nitrogen fertilizers.


By now, you have a good idea of how tomato blossom set spray works.  You also know when to use it, and what alternatives are available before you choose this method to get tomatoes.

You might also want to read my article on how to make tomato plants produce more fruit.

I hope you found this article helpful – if so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!


Jon M

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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