Broccoli is a cool weather plant, which means that it grows best in moderate weather. This also means that in many areas, broccoli can have a short window in which to grow well, so gardeners often find themselves struggling with broccoli that flowers instead of continuing to grow.
If your broccoli is flowering (known as bolting) before the head has finished growing, it could be bad news for the plant. Thankfully, there are a few potential causes for this, and all of them can be prevented.
So, why is your broccoli flowering?
The most common reasons broccoli flowers are the soil is too hot, too cold, or the plant undergoes too much stress. All of these issues are preventable, but once broccoli bolts, the plant might not grow anymore. Therefore, it is very important to try and prevent broccoli from bolting early.
Here are some ways to do that.
As we said, there are usually three main things that cause broccoli to bolt, or flower, early: heat, cold, and stress. Let’s take a look at each one of these, and how we can prevent them from negatively affecting your plants.
Again, broccoli is a cool-weather vegetable. It grows best in temperatures between 50-68°F (10 -20°C). For a lot of gardeners, this means there’s only a couple of months, or even weeks, in the springtime where broccoli has the best weather for growing.
While broccoli won’t necessarily die as soon as it gets above 68 °F (20°C ), this is one of the most common causes of early bolting, and as such can be a problem for your broccoli plants.
When broccoli flowers, the head stops growing. Parts of the plant grow longer and start to produce flowers. Once these flowers appear, the head will start to die. Even if you do harvest it before it dies, it will likely turn bitter as soon as the plant bolts.
So, you want to avoid your broccoli plants getting too hot. But how do you do that?
Luckily, what matters isn’t the temperature of the air itself, but the temperature of the soil, because it’s the roots that control most of the growth of the plant. If the roots get too warm, they will try to speed through the plant’s life cycle.
So the key is to protect the roots from getting too warm. There are a few ways to do this.
The first, and perhaps most obvious, is to plant broccoli as early as you can. Don’t plant too early, though, as too much cold can also harm the plants. Wait until all risk of frost has passed before planting. If you want, you can start growing your broccoli indoors, so you get a jump start on the season.
Mulching around broccoli plants can also help protect them. It provides an extra layer to soak up the sun, so the soil below doesn’t get as hot. This is good if you already have plants in the ground and the temperatures start to rise.
Watering more often is another option. Watering with cold (though not freezing) water will help keep the soil temperatures lower. You could also try getting row covers— but be sure to look for ones that lower the amounts of heat and sunlight, not trap it in.
On the opposite end of the spectrum, although less common, cold temperatures can also cause broccoli to form head and flower, or bolt early.
Once again, it’s the soil temperature that matters most. If the soil gets below 40°F (4°C) for a few weeks, it could cause the plants to bolt, ruining your chance at a great broccoli harvest.
In climates with snow or a hard freeze, the most important step to prevent this is not planting broccoli too early. Do not put it outside until a couple of weeks after the last frost, when the ground has thawed and temperatures are consistently warmer.
Mulch can also help with this. Because mulch absorbs temperature, it helps keep the temperature of the soil the same. So if you mulch before it gets cold, it will keep the soil warm longer. Again, row covers are an option; this time, the kind that is designed to increase heat.
You can also start your broccoli indoors and then transplant it later, so you can get a head start on the growing season so it matures before it gets too warm.
The final reason that broccoli tends to bolt early is stress. The reaction broccoli has to heat is an example of stress, but there are other things that can stress the plant and make it react in the same way. The most common stressors, aside from temperature, are long days, transplant stress and nutrient deficiencies.
Day Length Increases
As the days get longer going into summer, broccoli plants can sense the change. This tells them that the growing season is coming to an end, so they need to speed up their life cycle. Even if the broccoli head isn’t finished growing yet.
To prevent this, you don’t want to let the plant sense the longer days. If you have your broccoli in a spot where they only get direct light for half of the day, it can help. Having other plants nearby to shade the broccoli is also good. And for more direct measures, you can always set up netting to reduce the amount of sunlight the plants get, or angle nets to cut off sunlight at a certain point in the day.
Of course, broccoli needs light like most plants, so don’t cut it off completely! Just try to keep it protected, so it doesn’t get as much direct light and think the days are too long.
The second stress trigger is transplant shock. Transplanting is often necessary, but it can cause stress to plants, and some plants, like broccoli, are more susceptible to this.
The best way to minimize the stress is to transplant early. Let the plant establish itself a bit, but don’t wait until it gets too big. The ideal size for planting out broccoli seedlings is 2.5 inches (7cm). If the plant has well-established roots, it will be more stressed by a move. So plan your transplanting before the plant gets too big.
And if you do transplant, you can provide the plants with some extra nutrients to help them adjust to the new environment. A seaweed solution like this one can be very helpful in getting plants back to top shape.
Lack of Fertilizer
And thirdly, a lack of soil nutrients can stress the broccoli plant into flowering. As heavy nitrogen feeders, the addition of organic Bone Meal like this one promotes healthy growth for broccoli plants.
So, those are the three big things you have to worry about when it comes to broccoli flowering early: heat, cold, and stress. If you can prevent those things, then your broccoli should be able to grow nice and healthy! But what happens when you can’t prevent them?
The short answer is, sadly, no. While parts of the plant might continue to grow after bolting, it will not produce the way you’d like it to.
After broccoli bolts, the main head turns very bitter and then begins to wilt. Once this happens, the head will not grow anymore, and won’t grow back later, either.
Many broccoli plants have side shoots, like smaller heads around the main one. Sometimes, these shoots will continue to grow after the plant bolts. However, they don’t get very big, and won’t provide the same kind of harvest as the main head would.
Additionally, these side shoots might also be bitter. So while parts of the broccoli plant will continue to grow after flowering, the main plant will stop growing and will not grow back. Once broccoli bolts, it is most likely done for the season.
While its hope for a big harvest might be over, there are still some things you can do for a broccoli plant that has flowered.
First, you want to snip off the flowers. Luckily, pretty much every part of broccoli is edible (although not all the parts taste as good as the main head.) If you want, you can keep the flowers to eat raw or add to a salad. You can read more in our article: Eating Broccoli Leaves and Flowers With Recipe Ideas.
If the main head hasn’t wilted yet and is at least somewhat mature, you can try harvesting it now. The harvest might be small and a little bitter, but it’s worth a shot. And if you catch it early enough, it could still be delicious!
Once the flowers are removed, the side shoots on the plant might continue to grow. Again, they will be smaller, but it’s a possibility. So keep caring for the plant and providing it with good conditions, unless you are sure it is done growing for good.
Additionally, you can instead leave the flowers to attract pollinators into your garden. Bees love flowering broccoli! You can also then also wait for the flowers to develop into seed pods, dry out, and then collect seeds for the following season.
So, to recap: once broccoli flowers, or bolts, it is mostly done growing, and the main head will not grow back. It is in your best interest to prevent broccoli from bolting for as long as possible, but this isn’t always possible.
However, there are steps you can take. Try to protect your plants from both extremes in cold weather and too much heat. Try to minimize how much stress they’re under, and don’t transplant them too late.
If you follow the advice above, your plants have a much better chance of producing a full harvest before they bolt! Then, you’ll have lots of delicious broccoli to enjoy.