Last year I bought this dill seed since my Franchi wild fennel had done so well for several years. The plants look quite similar, and they are distantly related cousins; however it turns out they are actually less closely related than they look. The good news is that they share similar growing habits and needs. They do not hybridize together, so they can be grown nearby and with much the same care.
The biggest growing difference is that dill wants more sun than fennel needs. If you grow both in a semi shady area, you will notice the dill reduces its prodction more than the wild fennel does.
I think dill seed takes bit longer to take off than the wild fennel, and the dill plants are not as big. So in addition to my Franchi dill seed I bought a few dill seedlings in my garden center to jump start early. So there was some dill early, though my later plants from seed were bigger and more flavorful.
In the kitchen both the feathery dill and fennel foliage are oftenT interchangeable in my opinion. My spouse doesn't concur. Fennel is slightly sweeter, dill sharper. Both species have similar flowers which are ornamental in a rural sort of way. The seeds from both plants are very flavorful when ground. I'll continue to grow both every year.
Posted by Tom Andrews on 3rd Aug 2017