Whenever Brussels sprouts do not form heads, it usually corresponds with mistakes made as a novice gardener or mistakes that I have made myself. My first crop of Brussels sprouts were towers of leafy greens and I didn't manage to get a single sprout because I added nitrogen from chicken manure to the soil. Now, I test the soil exceptionally well each year before planting. Three primary reasons can be resolved immediately.
Overcrowding Solutions
- Thin seedlings to 24-30 inches apart
- Prune lower leaves weekly for airflow
- Use vertical supports to prevent shading
Nutrient Balance
- Switch to 3-15-15 fertilizer at 6 weeks
- Add bone meal for phosphorus boost
- Test soil boron levels monthly
Water Management
- Install drip lines for even moisture
- Mulch with 3 inches of straw
- Check soil at 4-inch depth daily
Soil testing eliminates the guesswork. My habit is to send soil samples to my state's extension service every 30 days of growth. When I received the results for August of last year, it was clear that my plants were experiencing a crippling deficiency of phosphorus levels, which I remedied by applying rock phosphate that I dug down about 8 inches deep. Within three weeks, the number of sprouts my plants produced tripled.
Watering practices can create crops or destroy them. My clay soil requires 1 gallon of water per plant every 3 days. Sandy plots? ½ gallon per day. But I still check my water in the soil two times per day: 7 AM moisture test and again 5 PM wilt check. Digital meters got me to stop overwatering.
It is more important to consider when to apply fertilizer rather than what to apply. I use fish emulsion when I plant, followed by bone meal at 4 weeks, and apply a kelp spray at 8 weeks. This is important because it stages the feeding of the roots first, and then the buds. Last fall, the harvest was double the previous season without any all-in-one fertilizer!
Read the full article: How to Grow Brussels Sprouts: Pro Tips for Big Harvests
