Broccoli is a cool season plant. It requires temperatures between 55 to 75 degrees to form heads. This summer has been too hot for broccoli to produce heads. I am not sure when you planted your broccoli. We planted our broccoli transplants at the end of April and the first of May and harvested the heads in June. If you planted it later it has been too hot for broccoli. Here in Columbus temperatures have been above normal for most of July and August around 90 during the day and cooling only to low 70’s at night. Extreme temperatures can hinder blooming especially when the temperature gets and stays above 80 degrees.

Choosing the right cultivar of broccoli is important. Some cultivars of broccoli do better in heat than others. In university trials Emerald Pride, Green Magic, Imperial and Monty are broccoli varieties that have shown heat tolerance.

Other factors could be 1) insufficient sunlight, Broccoli requires at least 6 hours of full sun per day. 2) Water stress, either too much or too little water. Again this summer has been challenging with the high temperatures increasing the plants demand for water and here at home heavy rains creating water-logged soils. Both overwatering and underwatering can negatively impact flower development. 3) Nutrient deficiency. Broccoli plants are heavy feeders and require a fair amount of nitrogen, phosphorous and potassium, though too much nitrogen can cause hollow stems and plants that have lush growth but do not produce flowers. Let me know if you have any additional questions.

For more information see Ohio Sate Estensions fact sheet: Growing Broccoli in the Home Garden | Ohioline

When did you plant the broccoli?