Broccoli Not Forming Heads: Heat Plus Stress Fixes
Broccoli not forming heads often comes down to heat, cold spells or stress early in growth. University of Minnesota Extension notes that summer heat harms the quality of the developing head. UC IPM adds that young plants exposed to several days of cold can form small, early heads, called buttons.
The short answer
Time the crop so heads form in cool weather. Clemson Extension notes that broccoli prefers average temperatures of 65 to 75 °F. Set out young transplants that have not been stressed. Water steadily, since University of Minnesota Extension notes that plants need steady water plus nutrients throughout growth.
Why does heat stop broccoli heads?
Heat hits the head, not the leaves. University of Minnesota Extension notes that summer heat harms the developing head, while heat during leafy growth is fine.
For spring crops, it suggests a variety with heat tolerance plus a short cycle of 50 to 60 days to harvest. Fall crops can use longer varieties so heads form in cooler weather.
What is buttoning?
UC IPM notes that broccoli may produce heads too early, resulting in small heads. This can happen after several days of cold temperatures.
UC IPM lists more causes: too little water, a shortage of nitrogen, excess salt or weed competition. Illinois Extension notes that plants left too long in seed flats may produce button heads soon after planting.
| Problem | Likely cause | Change |
|---|---|---|
| Tiny early heads | Cold spell or stressed transplants | Adjust planting dates plus use young plants |
| Poor heads in summer | Heat as heads form | Plant so heads form in cool weather |
| Slow, uneven growth | Dry soil or low nitrogen | Water steadily plus side dress |
Source: UC IPM plus University of Minnesota Extension.
How can I get full heads next time?
Start with young plants. Clemson Extension advises setting out young transplants that have not been stressed. Water thoroughly at planting to start root growth.
Illinois Extension suggests side dressing with nitrogen when plants are half grown. It also advises ample soil moisture, especially as the heads develop.
How to: step by step
- Choose a variety that fits the season.
- Plan planting so heads form in cool weather.
- Plant young, unstressed transplants.
- Water well at planting.
- Side dress nitrogen at half growth.
- Maintain even soil moisture as heads develop.
Troubleshooting
Small heads form early: cold or stress. UC IPM suggests adjusting planting dates where chilling may occur.
Plants grow but never head: heat or a mismatched variety. Plant a short cycle variety in spring or move to a fall crop.
Plants stall after planting: old transplants. Illinois Extension notes that plants left long in flats may button.
For related reading see heat stress, hardening off seedlings plus underwatering cannabis. Kind Seed Co also stocks cannabis seeds.
Sources
- Buttoning in broccoli plus cauliflower, UC Statewide IPM Program
- Growing broccoli in home gardens, University of Minnesota Extension
- Broccoli, Illinois Extension Watch Your Garden Grow
- Broccoli, Clemson Cooperative Extension
FAQ
What temperature does broccoli need?
Cool weather. Clemson Extension notes that broccoli is a cool season crop that prefers average temperatures of 65 to 75 °F. It adds that South Carolina gardens suit broccoli most in the fall season. Illinois Extension notes that broccoli develops well during the cool seasons of the year.
Why is my broccoli bolting?
Cold plus plant size play a part. Clemson Extension notes that bolting is a problem for spring planted plus overwintered crops. The larger the plants are at the time of a cold period, the higher the incidence of bolting. Sensitivity also depends on the variety, so choose slow bolting types.
Will broccoli make more heads after harvest?
Often, yes. University of Minnesota Extension notes that after the main head is harvested, smaller side shoots grow for another harvest. Illinois Extension notes that side heads develop after the large central head is removed. Plants can yield over an extended period when grown well.
When should broccoli be harvested?
When the head is firm. Clemson Extension suggests harvesting when the main head is 3 to 6 inches across plus the flower buds are tightly closed. Illinois Extension advises cutting the central head before it loosens plus before the individual flowers open to show bright yellow.
Can broccoli grow in fall?
Yes, plus often well. University of Minnesota Extension notes that most broccoli grows well as a midsummer planting for fall harvest. Varieties with a cycle of 60 to 85 days let heads form in cooler temperatures. It adds that broccoli continues to grow after the first light frosts in fall.
