Broccoli Fails to Form Flower Head
The secret to growing beautiful heads of great tasting broccoli starts with the weather. Cool weather, even a light frost at harvest time, results in a sweeter flavor.
But when young transplants are exposed to cold temperatures they often start forming heads prematurely. The small plants don’t have the reserves or leaves necessary to produce the energy to form a full head.
I planted some transplants that had already formed small heads while still in their containers, next to those that had not. I removed the small heads, planted and waited to see what would happen. They formed small flowering shoots instead of nice heads like the others.
Buttoning of broccoli can also occur when plants are exposed to drought or other stress that limits leaf growth and promotes premature flowering.
Avoid this problem in the future by protecting tender transplants from frost, then provide ample moisture, and proper fertilization.
A bit more information: Cauliflower is also subject to buttoning when exposed to cold temperatures or other stresses when it’s a small transplant. The long days and hot temperatures of summer can cause cauliflower curds to turn reddish purple and the leaves will grow through the head. When broccoli is exposed to these conditions it quickly forms flowers and seeds. This causes a bitter, less desirable flavor in both plants.