Why aren't my kohlrabi forming bulbs?
Written by
Julia Anderson
Reviewed by
Prof. Martin Thorne, Ph.D.Kohlrabi bulb failures frustrate gardeners, but there are solutions to that problem. When I grew kohlrabi the first time, I grew a whole bunch of leaves without any bulbs, and I learned about patience and proper care. Bulb formation is dependent on four key factors: spacing, the amount of water, the nutrient balance of soil, and temperature control. You must address each of these systematically.
Overcrowding
- Minimum spacing: 6 inches between plants
- Blocks sunlight to stem base
- Leads to elongated stems instead of bulbs
Water Stress
- 1-1.5 inches weekly required
- Dry spells cause woody texture
- Flooding splits developing bulbs
The nitrogen imbalance is especially difficult to manage. Kohlrabi requires some nitrogen early on, but having high levels of nitrogen after week 4 will cause it to divert the energy to the leaves of the plant. I have switched to using a 5-10-10 fertilizer once the bulbs start swelling. Soil testing every spring each year prevents this issue from happening again; my current crops are producing reliable baseball-sized bulbs.
Cooling Strategies
- Mulch with reflective straw
- Water at dawn to cool roots
- Use row covers as sun shields
Variety Selection
- Kossak Hybrid handles heat best
- Early White Vienna for quick harvests
- Avoid planting mid-summer in zones 7+
Having consistent moisture is non-negotiable. I lost bulbs to drought before installing drip irrigation with timers. Soil moisture meters help keep moisture levels at ideal 25% levels at root depth. For container growers, self-watering pots safeguard against extremes of over- and under-watering.
Read the full article: How to Grow Kohlrabi: Complete Beginner's Guide
