Fennel that grows bulbs is called Florence fennel or celery herb because it resembles bulb celery stalks. Florence fennel requires little maintenance while growing; the trick is to plant it at the right time. The plant has a tendency in too much heat to grow a tall stalk and seed instead of producing the bulb. The stalk and the bulb can be used for food, eaten raw or combined in recipes. USDA planting zones 3 through 6 must start the seeds indoors to have a good harvest.
Start seeds indoors for USDA planting zones 3 through 6. Start the plants three to four weeks before the last freeze date. Place two seeds per peat pot and cover with ¼ of an inch of peat. Dampen the soil. Keep the pots warm and moist by placing the peat pots on a tray with 1/2 inch of water in the bottom. Place the tray on the top of a refrigerator.
Place the seeds in bright, indirect sunlight after they begin to germinate. Water the seeds when the top of the peat pot feels dry. Take the plants outside in direct sunlight for 15 minutes during the third week. Increase the time by 15 minutes each day until they can handle a full day of direct sun.
Prepare the garden bed by removing all lawn grass, weeds and stones. Work 2 inches of compost into the soil for better drainage.
Plant seeds (USDA planting zones 7 through 10), or peat pots 2 feet apart with rows 2 feet apart. Seeds should be placed ¼ of an inch deep. Thin the seedlings to the strongest one when they reach 2 inches tall.
Water often enough to keep the soil moist.
Fertilize every two weeks with a diluted fish emulsion to keep nutrients in the soil and produce bulbs.
Hill the soil around the bulbs when they reach about the size of a large egg to keep the bulbs tender. Place mulch over the hilled soil to keep it moist, cool and stop the weeds from growing.
Harvest when bulbs are 2 to 3 inches in diameter. Snip the leaves anytime during the growing season to use for seasoning in your favorite recipes.