To grow fennel, the most important thing to consider is the timing: seeded or transplanted in April or May, the plants are certain to bolt to seed during the long days of early summer before forming a useable bulb. Heat and drought can also trigger flowering. All things considered, fennel is best grown as a “second season” crop to follow spring lettuce, spinach, radishes or peas. Coming to maturity during the cool, damp days of fall, fennel bulbs fill out slowly and stand for weeks in the garden without losing quality.
Fennel sprouts quickly from seed. Early July is the time to sow and there are two options: one is to start seeds in small (5 cm) peat or plastic pots using 2 or 3 seeds per pot, thinning in time to one strong plant, and then transplanting about 3 weeks later into a garden bed at a spacing of 20 to 25 centimetres in all directions. Alternately, sow seeds directly into the ground in a shallow furrow, one seed every 2.5 centimetres, gradually thinning—trying to re-plant thinnings is a wasted effort—to the distance above. Seeding in pots for later transplanting may be the more certain method, and gives a few extra weeks for whatever is occupying the fennel bed-to-be to wrap up. Be extra careful when setting seedlings in the ground, since fennel is thrown off by root disturbance. Either way, fennel appreciates fertile organic soil enriched with compost, very old manure and/or a granular natural fertilizer.
Caring for plants
Like celery, fennel thrives on an abundance of water—not the semi-boggy conditions that suit celery, but steady moisture from start to finish. A twice weekly soaking should suffice, and a deep drink of fish emulsion (or equivalent liquid fertilizer) at mid-growth will show results. A mulch of compost, grass clippings or leaf mould helps to suppress weeds and hold moisture. For a milder flavour, draw the mulch (or some garden soil) up over the expanding bulbs to block light—an easy (and optional) “blanching” technique.