Troubleshooting
Fennel problems — and how to fix them
Fennel (Foeniculum vulgare) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Bolting before bulb forms
Heat or transplant shock; use bolt-resistant varieties.
Inhibits nearby plants
Allelopathic — plant alone or with dill at most.
Swallowtail caterpillars on fronds
Beneficial pollinators; tolerate them.
Bulb cracks
Heavy water after dry spell.
Self-seeding
Cut heads before seed sets if you do not want spread.
Prevent fennel problems before they start
Most fennel issues are care-mismatch, not bad luck. Dial in the basics:
Fennel problems — FAQ
Why is my fennel bolting before bulb forms?
Heat or transplant shock; use bolt-resistant varieties.
Why is my fennel inhibits nearby plants?
Allelopathic — plant alone or with dill at most.
Why is my fennel swallowtail caterpillars on fronds?
Beneficial pollinators; tolerate them.
Why is my fennel bulb cracks?
Heavy water after dry spell.
Why is my fennel self-seeding?
Cut heads before seed sets if you do not want spread.