Fennel is day length sensitive and grows best in days that are getting shorter with cooler temperatures. Some varieties are more susceptible to bolting in long day and warm conditions. Fennel is not tolerant to heavy frosts.
Fennel Growing Information
Direct Seed: After last frost. Soil temperature for germination is 50-70° F.
Transplant:Start transplants 4-6 weeks before desired transplant date and plant out after last frost with special attention to root disturbance, as this will encourage bolting.
Spacing: Sow 2” apart in rows that are 18” apart, at ¼" depth. Thin direct seeded plantings or set transplantsat 6-12” apart.
Growth needs: Well-drained, fertile soil. Regular irrigation will encourage bulb growth. High heat and long days can encourage bolting.
Harvest: When bulb is filled out, cut right below base, above the taproot, and remove outer, smaller petioles.