Why Is My Broccoli Growing Tall and Flowering (Bolting)


You’ve been taking good care of your broccoli plants, and then they start to grow tall and flower.  Is this a problem, and if so, why does it happen?  I was wondering the same thing, so I did some digging (no pun intended) to find out.

So, why is your broccoli growing tall and flowering (bolting)?  Broccoli grows tall and starts to flower in order to form seeds and complete its reproductive cycle.  This happens when the soil temperature goes above 80 degrees Fahrenheit (27 degrees Celsius).  Sometimes this will happen even before the broccoli has a chance to form a large head.

Of course, there are steps you can take to prevent broccoli from bolting so quickly during the summer.  We’ll get into these steps, and also some other common broccoli problems, such as broccoli plants forming small heads or falling over.

Why Is My Broccoli Growing Tall and Flowering? (Broccoli Bolting)

Broccoli will start to grow tall and form flowers when soil temperatures climb above 80 degrees Fahrenheit (27 degrees Celsius), usually in the hotter summer months.  Broccoli is a cool weather plant, preferring soil temperatures between 65 and 80 degrees Fahrenheit (18 and 27 degrees Fahrenheit).  For more information, check out this article from Bonnie Plants on growing broccoli.

When the temperature rises, a broccoli plant will begin the next phase of its life cycle.  This means that the broccoli plant will grow tall, form flowers, and try to produce seeds in order to reproduce.  This is known as bolting, and it can affect the flavor of the broccoli.

Will Broccoli Heads Grow After Flowering?

No, broccoli heads will not grow after flowering.  If the soil gets too warm and a broccoli plant starts to bolt, then you have missed the train.

bolting broccoli
This broccoli has bolted (it is starting to flower and produce seeds). Image from: https://commons.wikimedia.org/wiki/File:Broccoli_Flowers.jpg

A broccoli plant wants to form seeds to reproduce.  Once it has done so, the plant is satisfied that it has completed its mission in life.  Therefore, it will stop growing a head.

To get a big head of broccoli from your plant, you will need to prevent it from flowering too early – more on this later.

When the head of broccoli is large and mature, harvest it by cutting it from the plant.  You will want to make sure to do this while the buds of the broccoli are still green and packed closely and tightly together.  If the buds start to separate and grow taller, cut off the head!

Usually, the head is mature when it has a diameter of 4 to 6 inches (10 to 15 centimeters), although some heads of broccoli can get up to 8 inches (20 centimeters).  Of course, the size of a broccoli head can vary by variety, so be sure to check the seed catalog.

broccoli head
Mature heads of broccoli can be 4 to 8 inches in diameter.

After the main head is cut off, you can harvest side shoots, which may be only 1 to 2 inches (2.5 to 5 centimeters) in diameter.  For more information, check out my article on how big broccoli plants get.

Can You Eat Broccoli That Has Flowered or Bolted?

Yes, you can eat broccoli that has flowered, but the main broccoli head will not grow well after flowering.  You can eat the flowers and any side shoots that grow, but they may become bitter, as many plants do after they go to seed.

You can also eat the leaves of a broccoli plant, meaning that it is not a total loss if the plant flowers early.  You could use broccoli leaves in a salad, or steam them just like spinach.  You can even eat the stems of broccoli if you want!

broccoli plant
Even if you don’t end up getting a large head of broccoli like this one, you can still eat the leaves!

Just be sure to avoid eating the seeds and roots of a broccoli plant, which are poisonous.

How To Prevent Broccoli From Bolting

You may feel powerless to prevent broccoli from bolting.  However, you have more control than you think.

First, when planning your garden, choose heat-resistant broccoli varieties.  These are less likely to bolt when hot weather comes around in the summer.

Also, choose fast-maturing broccoli plants.  The time to maturity of broccoli generally ranges from 50 to 100 days.  If you plant your broccoli early enough, you will avoid the possibility of the plants bolting, and you will enjoy big, healthy green heads of broccoli.

In addition, try planting your broccoli where it gets full sun (6 or more hours), but not too much sun.  Try to plan it so that the broccoli is shaded during the hottest part of the day, which is around 3pm.

sunlight through forest
Intense sunlight can raise soil temperatures and cause your broccoli to bolt, so try to keep them shaded for part of the day.

Finally, put a layer of mulch or compost over the soil near your broccoli plants.  This will prevent the soil from heating up so quickly on a hot day. For more information, check out my article on compost and mulch.

As a last resort, you can try watering your plants with cold water to cool them off.

Other Problems With Broccoli Plants

There are a few other problems that you may encounter with broccoli – here are a few of them, along with an explanation for why each one occurs.

Why Are My Broccoli Plants Falling Over?

Your mature broccoli plants may fall over if they bolt due to hot weather and become very tall.  This is especially likely after the plant flowers and goes to seed.

Younger broccoli plants in the garden may fall over due to pest or disease damage.  For example, cutworms love to chew through the stems of young, tender plants before they become too tough.  For more information, check out my article on how to get rid of cutworms.

Broccoli seedlings may fall over if they become “leggy”, or long and spindly, due to reaching higher for a limited light supply.

Why Are My Broccoli Plants Producing Small Heads? (Broccoli Buttoning)

Broccoli plants will button, or produce small heads, for several possible reasons.  One of the main reasons is exposure to cold while they are young and still developing.

Broccoli Buttoning Due To Cold Exposure

Although broccoli prefers cool weather, they do not necessarily like extreme cold.  Exposure to cold temperatures of less 40 degrees Fahrenheit (4 degrees Celsius) for a week or more can cause broccoli plants to form small heads.

frost
Cold and frost can damage broccoli plants so that they will never produce large heads.

Buttoning is more likely if the broccoli plant is exposed to frost.  According to the Texas A&M Extension, temperatures of 26 to 31 degrees Fahrenheit (-3 to -1 degrees Celsius) will burn the leaves of broccoli plants, but may not kill them.

Your broccoli plants are more likely to be exposed to cold temperatures if you plant too early in the spring, or too late in the fall for a 2nd harvest.  To protect your plants from cold outside, use cloches or row covers.  For more information, check out my article on how to protect plants from cold and frost.

You can also start your plants early, growing them from seeds indoors to protect them from the worst of the cold.  Be sure to check frost dates before transplanting broccoli outside.  For more information, check out this frost date calculator from the Old Farmer’s Almanac.

Broccoli Buttoning Due To Lack Of Water Or Nutrients

Broccoli may also button due to stress caused by a lack of water or nutrients.  Especially in the hot, dry summer months, you will want to make sure your plants are adequately watered.

If you have problems with dry soil, you can try mixing compost into your garden, and adding a layer of mulch over your topsoil.

The compost will help the soil to retain water, and the mulch will insulate the soil and prevent the sun from evaporating water so rapidly.

For more information, check out my article on how to treat dry soil.

garden hose
Be sure to water your broccoli adequately – but not too much.

Keep in mind that it is also possible to over water plants – for more information, check out my article on the signs of over watering plants.

If water levels are fine, then you will want to check the soil pH next.  Broccoli plants prefer a soil pH of 6.0 to 6.8 (slightly acidic to neutral).

If your soil pH is far outside of this range, then your broccoli plant may suffer a nutrient deficiency, due to unavailability of nutrients in the soil.  For more information, check out this article from Research Gate on the effect of soil pH on nutrient availability.

A soil test is really the only way to find out exactly what your soil pH is.  You can buy a do-it-yourself test kit online or at a garden center.

However, you can also send a soil sample to your local agricultural extension office for testing.  If you send information about what you are growing, the lab can also send back recommendations on how to treat your soil.  For more information, check out my article on how to do a soil test.

If your soil pH is fine, then you should consider the possibility of a nutrient deficiency in your soil.  Generally, a soil test will also tell you about such problems.

Broccoli plants are considered heavy feeders, so they want lots of nitrogen.  Adding compost to your soil and using a balanced fertilizer that provides nitrogen, phosphorus, and potassium should provide your broccoli plant with the nutrition it needs.

Still, you should be careful with stronger fertilizers.  It is possible to burn your plants with fertilizer by adding too much at once, especially during dry weather.  For more information, check out my article on over fertilizing your plants.

Why Are My Broccoli Plants Not Producing or Forming Heads?

Broccoli plants can become damaged during handling when they are young and vulnerable.  This is more likely if you transplanted them from your house or a garden center instead of growing them from seed.

In this case, the broccoli plant may never form a head at all.  Instead, you may need to settle for using the leaves of the plant for a salad or steaming them like spinach.  Better luck next year!

Conclusion

By now, you have a much better idea of why your broccoli plant is growing tall and flowering.  You also have some methods to prevent the problem going forward.

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 broccoli flowering (bolting), 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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