Periwinkle, Ivy and St. John's Wort EVERYWHERE

[AyealaB]

Hi there,
We have decided to move ahead on our chicken adventure finally. The first substantial obstacle we've come up against is the immense amount of toxic ground cover on our property. We have Periwinkle, English Ivy and St. John's Wort everywhere. We found one spot that is mostly bare to utilize for the coop and extended run area but even there I'll have to clear Periwinkle and possibly sheet mulch the area before we get our pullets in the fall.
Has anyone on here successfully cleared Periwinkle?
If I miss some will it kill them instantly? Should we just give up now before starting?
I have some time to handle this issue I'm just worried it will keep poking up and that the chooks will be able to access the immense root body of this noxious toxic weed.

 

[CluckerFamily]

My flock free ranges all day and they can roam by my periwinkle patch. They don’t eat it, they will walk right over/through it to the other side of the patch to eat the grass or bugs.

 

[Mamatomany123]

My flock free ranges all day and they can roam by my periwinkle patch. They don’t eat it, they will walk right over/through it to the other side of the patch to eat the grass or bugs.

I on the other hand think my chickens would eat it. They're not the brightest crayons in the box. 2 of them spent 20 minutes chasing down a feather flying in the wind because they thought it was a bug. Then spent another 20 minutes grabbing it from eachother and chasing one another.