Anthriscus sylvestris, cow parsley, should be regarded as being a well behaved plant. In its green or purple, Ravenswing, forms it flowers for quite a good spell and then subsides as quickly as it appeared, as if it had not been there.
Multiplying with ease each year it can create a sea of frothy flowers each May which sit happily in woodland and perennial borders alike. If in the latter cut its thin form down quickly after flowering to allow later emerging plants their proper chance.
People generally like cow parsley, it is very English and its fullness and softness gives us comfort every year.