Grow fennel by itself as it is not liked by a lot of other plants.
Harvesting Fennel Seeds : Harvest only when the seeds are completely mature (late Autumn / Fall) Dry out by spreading the seeds in a thin layer over a screen in a cool dark place. Make sure the area is well ventilated and check often to turn the fennel seeds over to make sure all sides dry completely. After drying, store in an airtight container until use.
Seed viability is four years.
These estimates for how long Fennel takes to sprout, grow and harvest are from real observations from real gardeners, right around the world.
Average 10 days | Min 5 days | Max 22 days (29)
Average 46 days | Min 25 days | Max 68 days (7)
Average 277 days | Min 154 days | Max 1331 days (7)
Dried fennel leaves protect dogs from fleas when the leaves are put inside the dog’s house.2
Sweet fennel, Bronze fennel
Foeniculum vulgare Mill.
2 “Our herb garden” entry on fennel":ourherbgarden.com/fennel-companions.html