Florence fennel is grown for its bulblike stalk, while regular fennel is grown solely for its herby foliage. Both the bulb and the edible foliage of Florence fennel have a sweet, licorice-like flavor. The seed is sometimes sold as sweet fennel or under its Italian name finocchio.
Florence fennel likes a sunny spot in fertile, well-drained soil. Do not plant fennel near beans or tomatoes as it hinders their growth. Work a generous amount of compost into the beds with a garden fork.
For the best chances of success, sow the seeds in mid- to late-summer as fennel will bolt when grown in the hottest part of the season. Plant the seeds 1/2" deep every 4" in rows spaced 24" apart. Cover with soil and water well.
When seedlings sprout, thin to one plant every 12". Mulch the plants with pine straw or other organic mulch to insulate the soil, maintain moisture and prevent weeds. The soil should be kept evenly moist but not wet. Fennel grows best when it's provided with steady but moderate amounts of fertilizer.
Some gardeners mound soil or mulch around the bulb when it reaches 2" to block the sun and keep the bulb a pale white color.
Most varieties of Florence fennel take between 75 and 120 days to mature from seed. When the fennel is about 12" tall, begin harvesting some of the feathery foliage to use as an herb. Once the swollen bulb is about 3" to 4" wide, it is ready to harvest. Use a sharp knife to slice off the plant right at the soil line. The entire plant is edible.