Every time I think I have seen everything my garden can throw at me, I have to eat my words. My garden is a challenge that constantly changes. This year, our Maine weather has been odd to say the least. We had pretty intense drought conditions in the spring when it is normally wet. And, then we had heavy rainstorms throughout the month of August when it is usually dry. Because of these weather conditions, I have encountered some brand new issues in my garden. One of these new issues has been Broccoli Soft Rot. Broccoli Soft Rot (aka Head Rot) is what causes Black Broccoli Heads. So, let’s take a moment to look at what causes Broccoli Soft Rot and how to help prevent it in the future.
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What Causes Black Broccoli Heads?
Typically, the culprit here is Soft Rot (also known as Head Rot when referring to Broccoli). Soft Rot is a bacterial or fungal growth that causes the Broccoli heads to decompose. It can also spread further and affect the stems of the plant as well. As I mention in my post on Common Gardening Mistakes, it is very easy to have what seems like a “small issue” become a huge crop loss. Soft Rot is one of these, since it can appear very innocent in its early stages.
There are 2 main types of Broccoli Soft Rot:
- BACTERIAL HEAD ROT: This is what causes black broccoli heads that eventually become very soft and extremely smelly. According to the University of Wisconsin, bacterial soft rot is typically caused by certain species of Pectobacterium, Dickeya, Pseudomonas, Clostridium, and Bacillus.
- FUNGAL HEAD ROT: Is caused by various forms of the Alternaria fungus. This looks very similar to Bacterial Rot, but causes less soft breakdown of the plant and is noticeably less smelly.
Why Does Broccoli Soft Rot or Head Rot Happen?
Most experts agree that Broccoli Rot does not happen to healthy, uninjured plant that is receiving good nutrition. Typically, the bacteria or fungus takes advantage of a weakened plant or area of the plant and then spreads from there.
A broccoli plant can be damaged by the following things, to name a few:
- Heat
- Over-Zealous Weeding
- During Harvesting
- Fertilizer Burn
- Insects
- Hail
And, there are other factors that can pre-dispose a plant to Broccoli Soft Rot, or make it worse once an infection has begun. These factors include:
- Excessive Rain
- Humid Weather
- Calcium Deficiency in the Soil
- low pH of the Soil
- Overhead Irrigation
- Using Contaminated Tools Between Plants
- Overcrowding of Plants
- Not Rotating Crops
- Planting Susceptible Varieties of Broccoli
What are the Stages of Broccoli Soft Rot?
So, since bacteria or fungi are what causes black broccoli heads in your garden, what does it initially look like? Initially, it will look like the creamy and tan patches shown in the photo below (more likely to be fungal). Or, it will look like a dark, water logged area of the head (more likely to be bacterial, but can also be fungal).
From there, the heads will begin to turn progressively darker as they rot. They will turn dark brown and eventually black as they decompose. And, the infection will start to affect larger portions of the head.
Finally, the entire head will turn black and rot away. At this point, the infection will often be affecting other areas of the plant as well.
Just remember that bacterial tends to smell a lot worse and get a much softer rot than the fungal form.
Can Broccoli Head Rot be Treated?
The general consensus seems to be that it ranges from very difficult to impossible to treat. There are a few ideas that might help. But, prevention is more important since there does not seem to be any reliable cure.
A few ideas to possibly treat and/or slow down the progression of Soft Rot (what causes black broccoli heads):
- As soon as a plant becomes infected, remove it and burn it. Do not compost it into any garden area or garden material. The infected plant material will raise the bacteria or fungi level in that area.
- If the plants are crowded, you can thin them out (remove the weaker looking ones or any plants with possible early signs of deterioration). This will dry out the remaining plants.
- Try to do a better job of controlling any watering you are doing. Obviously, you cannot control the rainfall.
- Some folks try either bactericides or fungicides, but there does not seem to be much research showing that they are effective. And, personally, I grow organic broccoli. So, I wouldn’t attempt to use them anyway.
If Soft Rot is what causes Black Broccoli Heads, then how do I prevent it?
It is typically much easier to prevent what causes black broccoli heads. So, here are 13 tips for your future broccoli garden:
- Use drip irrigation instead of overhead.
- Be gentle when weeding and harvesting and avoid any unnecessary damage to the plant. Any wound is an invitation.
- When harvesting, cut stems at an angle. A straight cut will leave a flat area for water to collect.
- Avoid insecticides, since these can actually make broccoli rot worse.
- But, keep up with any organic insect control that you use, since insect damage can predispose a plant to head rot infections.
- Space your plants out. Overcrowding can lead to extra moisture retention and doesn’t allow the plants to quickly dry out after watering or rain.
- Plant rot-resistant varieties, and avoid broccoli varieties that have flat heads. A tight, domed head will help shed water.
- Immediately remove any plants that become infected and burn them. Do not keep them in your garden or put them in your compost.
- Make sure that soil pH and calcium levels are appropriate.
- Plant in well-drained soil.
- Rotate crops (do not plant a Brassica crop in that area for a minimum of 3 years).
- Sanitize gardening tools if they have been used on infected plants. Rubbing alcohol is one of the recommendations for this, although it can be corrosive to your tools over time.
- Do not harvest during rainy or wet conditions.
Are the Black Broccoli Heads Edible?
The simple answer to this is: it depends.
If you have a large broccoli garden and only a couple of your plants are affected by Head Rot, then I wouldn’t bother with trying to eat them.
If the broccoli has progressed past the first stage, then don’t eat it (gross!).
The only time you could try to eat this broccoli would be in the earliest phase when it only has a small spot of rot starting to develop. Simply cut it out, and wash the head with fruit/veggie wash. I haven’t noticed that this affects the taste or texture of the rest of the head. But, it really is only worth doing if you have a limited amount of broccoli.
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