Florence fennel (Foeniculum vulgare) produces large white bulbs that can be sliced and eaten as a vegetable, as well as attractive feathery foliage and aromatic seeds that are prized as a flavoring in sausage, teas and other dishes. Some people grow fennel as an ornamental in the garden. The feathery foliage provides an attractive backdrop for flowers. Some varieties turn bronze in the fall. However, there are a few cons of growing Florence fennel.
Fennel produces a lot of seeds, a plus if you're growing it for the seed, but a negative if you don't want it to take over the garden. Fennel can reseed itself annually and spread rapidly, crowding out other plants. According to Cheryll Greenwood Kinsley of Washington State University, the only way to prevent this is to snip off the seed heads before they fully develop. Once the seed heads mature, they burst open and scatter seed over a wide area.
Fennel is a heavy feeder and can deplete the soil where it's planted, making that area of the garden unsuitable for other plants. Use plenty of composted manure of a general garden fertilizer to keep both fennel and your garden healthy.
The horticulturalists at Washington State University caution against letting the juice from fennel plants come into contact with your skin; it can be irritating and cause redness and rash in some people, particularly if you get the juice on your skin then expose the skin to sunlight. Wear gardening gloves when handling fennel plants.