Fennel can become invasive, it self seeds prolifically.
Having said that, it is a very light and feathery plant so although it pops up all over the place, it doesn’t feel like it is smothering all the other plants.
In spite of the wonderful aniseed scent and flavour of this herb, they are prone to aphid attack, so become less desirable unless you don’t mind the odd aphid in your salad. Fennel also has a long tap root, they are easy to pull out when the plants are young but trickier as the plant establishes itself.
So if you like insect friendly plants that are tall, light, feathery and edible, grow some fennel – if not then go purple and choose Thalictrum!
A good tip is to cut off the flowerheads before the seed has a chance to set. The dilemma is the seeds are the best tasting bit.
We haven’t used Fennel in any of our small garden designs – but we do use lots of other plants that are much better (we think).
Why don’t you take a look