Browning

Browning is not something that takes place in a sauté pan. It is a symptom of boron deficiency in cauliflower characterized by hollow stems and curds that turn brown and bitter.

Cauliflower head browning (WikiGardener) Public Domain

How do plants use boron?

Boron (B) is a micronutrient that helps maintain plant cell walls. It helps produce and transport sugars, seeds, pollen, and flowers. And it helps metabolize nitrogen. In the world of plant food, micronutrients are only used in tiny amounts, but they are critical to plant growth. The optimal range for boron found in a soil sample is 0.1-0.5 parts per million (ppm). The only way you can determine how much boron is in your soil is with a laboratory soil test. Take my word for it, it’s the best investment you can make in your garden, next to mulching. Back to browning.

Browning symptoms

This disorder initially appears as water-soaked areas on the primary stalk and curd surface. As the plant continues to grow without enough boron, those darkened areas end up lining the now hollow stalk, and brown or pink patches develop on the curd. Because of how this disorder looks, it is often called brown rot or red rot. Whatever you call it, the curd will taste as bitter.This is not the same thing as the brown spots that occur in your refrigerator because of oxidation. [I guess you could say that those cauliflowers are rusting, but I digress.]

Oxidized cauliflower (Bicanski) Pixnio

Browning also causes the leaves to turn from dull green to yellowish-green, especially at the leaf tips. Leaves may also be smaller than normal. Since boron is an immobile nutrient, these symptoms are more frequently seen in newer growth. Seedlings may die from browning.


These other crops are affected by boron deficiency:

• Beets develop cankers on roots and internal brown rot.
• Cabbages have distorted leaves and hollow stems.
• Celery stems crack, and the inner tissue becomes reddish-brown.
• Celeriac leaf stalks crack, and the inner tissue becomes reddish-brown.
• Turnip roots develop gray concentric rings.

Cauliflower stem exhibiting boron deficiency (WikiGardener) Public Domain

Browning management

Boron deficiencies are more common in areas with frequent rainfall and acidic soil. If a lab-based soil test indicates a boron deficiency, you can apply borax to your soil. How much your soil needs will depend on how much is already there. Too much can be just as bad as not enough. If you need help figuring it out, you can always contact me. Boron-deficient heads that otherwise look normal may be saved if they are protected from sun exposure. You can do this by simply pulling leaves up and around the curds and tying them in place with a string. If the deficiency is bad, the curd will still taste bitter.


If you grow cauliflower, a soil test is a good investment.

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And if you happen to have better photos that I could use, please let me know. Thanks!