I've never grown fennel... but I have an idea for you.
Do you have access to large amounts of cardboard?
If so you can build a large lasagna bed instead of working hard to till up some weedy dirt.
Basically pile a bunch of cardboard on top of the area you want to garden, then pile some organic matter on top (grass clipping, mulch, leaves). You can continue going adding layers (hence the term lasagna) if you like, but one of each is really all that is necessary.
Next year you'll have rich organic weed free soil underneath it all, without having to touch a shovel. The cardboard and organic matter will of course have decomposed, but not before killing everything underneath them.
If you don't have a lot of cardboard but do have a truck, any time you're in the lansing area you're welcome to pick up as much as you can haul away from my house. Running an ecommerce business results in a lot of it.