The fennel plant, also known as Foeniculum vulgare, grows natively in the Mediterranean and is cultivated throughout the world in temperate regions. A tender perennial, fennel plant reaches up to 1.6 m (5 feet) in height and produces aromatic leaves and seeds often used for culinary purposes. Fennel self-seeds easily and typically reaches maturity in about 100 days. Gardeners also value the plant for its ability to attract beneficial insects to the garden, particularly the caterpillar of swallowtail butterflies.
Place your fennel plant in an area that receives at least six hours of full sunlight each day. Provide high-quality, well-drained potting soil if growing in a container, or well-drained garden soil if growing in the ground. Plant in spring after all threat of frost is over. Space fennel plants at least 33 cm (12 inches) apart.
Water once or twice per week as necessary to keep the soil slightly moist. Fennel plant tolerates drought but performs best when watered regularly. During extreme heat, container-grown plants may require daily watering. Never allow the soil to dry out completely.
Stake the fennel plant if it's growing in a windy location to prevent damage. Once the plant reaches 50 cm (18 inches) in height, place a stake in the ground and use garden twine to loosely secure the plant's stalk to the stake. This will prevent it from falling over during heavy winds.
Apply a 12-cm (4-inch) layer of organic mulch over the soil surrounding fennel plant in late fall, just before the first frost of winter in your area. This will prevent the plant from sustaining cold damage. Remove the layer in spring after all danger of frost has passed to allow new growth.
Prune fennel plant to the ground after the first hard freeze of the year. This will help the plant survive winter. Cut back branches by several inches throughout the growing season to promote a bushier growth habit, if desired.
Remove faded or dying flowers from your fennel plant, a process known as deadheading, to prevent aggressive reseeding. Allow some flowers to remain and turn to seed to replace plants that die, but remove most flowers for the best results.
For the best results, use evergreen boughs or straw to mulch your fennel plant. Fennel requires no supplemental fertilisation to thrive and well-fertilised soil can even cause the plant to lose its aromatic oils and distinct flavour. Feed only in extremely poor soil and use fertiliser diluted to half the strength recommended by the manufacturer.
Plant fennel away from other garden plants, as cross pollination could occur. Never plant fennel near bush beans, caraway, coriander or tomatoes.