Fennel

Florence fennel — the bulbing kind grown as a vegetable — is a plant with a narrow window of cooperation. It wants cool weather, steady moisture, and no sudden changes in temperature or water availability. A week of heat or a dry spell during the critical bulb-swelling phase can send the plant straight to bolt, which means a tall flower stalk and no edible bulb. The seed is beautiful, the flowers feed beneficial insects, but the gardener who wanted fennel for the dinner table is left with nothing.

The distinction between herb fennel and Florence fennel matters. Herb fennel is a tall perennial grown for its feathery leaves and seeds; Florence fennel is an annual grown for the swollen leaf base that forms a white bulb at ground level. They are the same species, different varieties, and the seed packets are not always clear about which you're buying. If the packet says 'bulbing' or lists a variety name like Orion or Romanesco, you have Florence fennel. If it just says 'fennel' with no mention of bulbs, it is likely the herb type.

Timing is the hardest part of growing fennel successfully. Spring sowings can work in cool climates, but in most regions the lengthening days and rising temperatures of late spring trigger bolting before the bulb has time to develop. Fall plantings — sown in late summer to mature in the cool weeks of October or November — tend to produce larger, sweeter bulbs with less risk of premature flowering. Sow about twelve weeks before your first fall frost, direct into the garden, and thin to one plant every twelve inches.

Fennel is allelopathic, which means it releases compounds into the soil that suppress the growth of many neighboring plants. Tomatoes, beans, peppers, and most brassicas tend to perform poorly when planted near fennel. The traditional advice is to give fennel its own corner of the garden, away from the main beds. Dill is one of the few plants that seems unbothered by fennel's presence, though even dill can cross-pollinate with fennel if both are allowed to flower, producing seeds with muddled flavor.

Water consistently once the bulbs start to swell. Uneven watering causes the outer layers to crack and split, and a plant that goes dry and then gets drenched may bolt as a stress response. Mulching around the base helps maintain even soil moisture, and a light hilling of soil around the developing bulb as it swells tends to blanch the outer layers and keep them tender.

Harvest when the bulb reaches the size of a tennis ball — usually three to four inches across. Waiting longer in hopes of a larger bulb increases the risk that the plant will decide to flower instead. Cut the bulb at soil level, trim the stalks to an inch or two above the bulb, and use the feathery tops as an herb if you like the anise flavor.