Why Is My Broccoli Plant Turning Brown? (3 Ways to Avoid It)


Are you worried about your broccoli plant turning brown on the head, leaves, or stem?  If so, you are probably wondering what is wrong, and what you can do about the brown stuff on your broccoli.

So, why is your broccoli plant turning brown?  A head of broccoli will turn brown due to brown bead, which is often caused by a lack of water or nitrogen.  The leaves of broccoli will turn brown due to rot caused by viruses and bacteria.  The stalk of a broccoli plant will turn brown due to boron deficiency.

Of course, there are ways to prevent your beloved broccoli plants from turning brown so that you can get a good harvest.

In this article, we’ll talk about what causes broccoli to turn brown and how to treat the various causes.

Let’s begin.

Why is My Broccoli Plant Turning Brown?

Many things can cause your broccoli to turn brown, depending on what part of the plant is browning:

  • Head – a head of broccoli will turn brown due to brown bead, often caused by a lack of water or nitrogen.
  • Leaves – broccoli leaves will rot and turn brown due to various bacteria and fungi
  • Stem – the stem of a broccoli plant will turn brown due to boron deficiency.
brown bead broccoli
Brown bead will cause the head of broccoli to turn brown.

We’ll start by taking a closer look at brown bead: what it is, what causes it, and how to prevent it.

Broccoli Head Turning Brown (Brown Bead)

According to the North Carolina State University Extension, brown bead is:

“a broccoli disorder that can be caused by poor growth, disease, or excessive temperature. It is typified by flowers that are small, turning brown, and not growing.”

https://growingsmallfarms.ces.ncsu.edu/growingsmallfarms-broccoliproblem06/

In a broccoli plant suffering from brown bead, the head (the part we harvest and eat!) will often grow just fine.  However, the green buds we are used to seeing on the head start to turn yellow at first, and then they eventually turn brown.

broccoli head
The green buds on a head of broccoli will eventually turn yellow and brown due to brown bead.

It’s bad enough that brown bead gives broccoli heads a poor and unappetizing appearance.  Even worse, brown bead promotes the growth of rot during rainy weather.

Brown bead is often caused by a lack of water or a lack of nitrogen.  Other factors, such as intense sunlight and high temperatures, can cause a lack of water, which can in turn cause brown bead.

How to Prevent Brown Bead

Fortunately, there are some ways to prevent brown bead.  We’ll start at the beginning, with your choice of broccoli varieties.

Choose Fast-Maturing Broccoli Varieties

According to the North Carolina State University Extension:

“Research has shown that fast-developing broccoli plants tend to be less susceptible to brown bead.”

https://growingsmallfarms.ces.ncsu.edu/growingsmallfarms-broccoliproblem06/

Broccoli that matures faster is also able to avoid the worst of the summer sun and heat, avoiding the lack of water that can cause brown bead.  So, if you choose fast-maturing varieties of broccoli, then you might be able to avoid brown bead altogether. 

Some broccoli varieties take 70 days (10 weeks) or more to mature, but there are some that mature in as little as 20 or 30 days (3 to 4 weeks)!

flowering broccoli
Choose fast-maturing broccoli varieties to avoid the summer heat and drought that can cause brown bead.

Here are some fast-maturing broccoli varieties from Johnny’s Selected Seeds:

Once you choose the right broccoli variety for your garden, it’s time to care for the plants properly.  Watering is a good place to start.

Water Evenly and Regularly

According to the North Carolina State University Extension:

“A regular supply of water also decreases the incidence and severity of brown bead.”

https://growingsmallfarms.ces.ncsu.edu/growingsmallfarms-broccoliproblem06/

So, not only does watering make it less likely that brown bead will occur, but it makes the problem less severe if it does happen.

According to the University of Minnesota Extension, broccoli plants will produce poor-quality heads if there is any water stress during the growing season.

To provide enough water for broccoli, water deeply as often as necessary to keep the soil moist.  When you water, dig down to feel the soil, and let the water soak down to a depth of over 2 inches.

watering can
Keep the soil moist for broccoli to avoid brown bead.

If your soil is sandy, you might need to water more often, since sandy soil drains fast.  High temperatures and dry weather will also mean that you need to water more often, since water will evaporate from plant leaves faster (due to transpiration).

To cut down on the time you spend watering, mix compost into sandy soil to improve water retention.

Also, add a layer of mulch over the soil to help retain moisture.  That way, you won’t need to water as often.

If dry soil continues to be a problem, you can learn how to treat it in my article here.

Just remember to water your broccoli plants from below, and do it in the morning.  If you wet the leaves in the evening and let them stay wet overnight, it increases the chances of rot caused by viruses and bacteria (more on this later).

Add Plenty of Nitrogen to Your Soil

According to the North Carolina State University Extension, when it comes to brown bead:

“A study showed that broccoli under higher nitrogen application rates had less incidence of the disorder than plants under lower N rates.”

https://growingsmallfarms.ces.ncsu.edu/growingsmallfarms-broccoliproblem06/

According to Clemson University, broccoli is a heavy feeder, so it needs lots of nitrogen and other nutrients to produce a healthy head.

Clemson suggests applying nitrogen to broccoli plants at the following times:

  • Pre-season – use 10-10-10 fertilizer and apply 2.5 pounds per 100 square feet before sowing seeds or transplanting broccoli seedlings.
  • Post-transplant – use calcium nitrate (15.5-0-0) and apply 2 pounds per 100 feet of row.  For direct-seeded broccoli, wait until the plants are 6 inches tall.
  • Supplemental – during the rest of the growing season, you may need to apply more fertilizer, especially if your soil is sandy or if heavy rain causes nitrogen to leach away.
broccoli head
Broccoli needs lots of nitrogen to produce big, green heads.

If you don’t know what the numbers 10-10-10 mean when referring to fertilizer, you can learn all about it in my article here.

Before you apply fertilizer, follow the directions on the package and water it in afterwards.  After all, using too much fertilizer at once can burn your plants.

If you are unsure about how much fertilizer to use, get a soil test through your local agricultural extension office and let them know that you are growing broccoli.  That way, they can give you recommendations for proper fertilization.

You can learn more about soil testing here.

Broccoli Plant Leaves Turning Brown

When the leaves on your broccoli plant turn brown, the most likely culprit is rot due to bacteria or viruses.  Here are a few of the most common ones.

Alternaria Leaf Spot

According to Penn State University, Alternaria leaf spot is caused by a fungus, Alternaria brassicae, which can infect most brassica species.  The disease is more likely to emerge in warm, rainy weather.

Alternaria leaf spot causes small spots to form on broccoli leaves.  These spots will turn brown or gray, and may be round with concentric rings.

To prevent the disease, use crop rotation and avoid planting members of the brassica family in the same spot in the garden every year.

Black Rot

According to Penn State University, Black Rot is caused by the bacteria Xanthomonas campestris.  The disease emerges in warm and humid conditions, and can spread by:

  • infected seeds
  • splashing water from rain or irrigation
  • insect movement

To prevent the disease, use crop rotation and avoid planting members of the brassica family in the same spot in the garden every year.

Also, avoid splashing water and soil onto plant leaves when watering.  A layer of mulch over the soil may help to prevent such splashing.

Downy Mildew

According to Clemson University, Downy Mildew is caused by a fungus, Peronospora parasitica, which can infect seedlings and mature plants alike.  The disease is more likely to emerge in moist conditions.

First, a gray mold develops on the bottoms of leaves.  Then, the tops of the leaves turn yellow and eventually brown before they wither away.

To prevent the disease, choose broccoli varieties that are resistant to the disease.  Water plants from below to avoid getting the leaves wet.

Remove any debris from broccoli plantings after you harvest at the end of the season.  Also, use crop rotation and avoid planting members of the brassica family in the same spot in the garden every year.

Ring Spot

According to Penn State University, Ring Spot is caused by a virus, Mycosphaerella brassicicola.  The disease emerges in cool, moist conditions and is typical in the fall.

Ring spot starts off as purple spots on broccoli leaves.  Later, the spots become brown with olive green borders.  The leaves may also become dry and curl up.

To prevent the disease, avoid getting the leaves wet by watering from below.  Also, use crop rotation and avoid planting members of the brassica family in the same spot in the garden every year.

Broccoli Plant Stems Turning Brown

If the stems on your broccoli plant are turning brown and there are no obvious signs of disease, then the problem could be due to a boron deficiency.

Boron is an important nutrient for plant growth, but it is needed in much smaller amounts than the “big three” nutrients (NPK, or nitrogen, phosphorus, and potassium) or even secondary nutrients such as calcium, magnesium, and sulfur.

However, if you grow the same plant (such as broccoli) in the same place for many years in a row, you could end up with a nutrient deficiency in the soil.

broccoli plant
Although needed in lesser amounts than nitrogen, boron is still important for broccoli plants.

According to Washington State University, broccoli and other brassicas (such as cabbage) have relatively high boron needs.

When broccoli plants lack boron, their stems become cracked, corky, hollow, and discolored.

According to the University of Massachusetts, a boron deficiency can occur in broccoli when the soil is too acidic or too alkaline (low or high pH).

Dry or sandy soil that lacks organic material (from compost or manure) will also lose boron faster due to leaching.

To treat boron deficiency, use a boron fertilizer such as Borax or boric acid.  However, get a soil test before adding anything to your soil!

A soil test confirms that the problem really is a boron deficiency.  It will also tell you how much boron fertilizer to use to address the problem.

Remember: it is easier to add more boron to the soil later than to remove it if you add too much!

Conclusion

Now you know why your broccoli plant is turning brown on the head, leaves, or stem.  You also know the steps to take to help prevent the problem.

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!

~Jonathon

jonathon.david.madore

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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