Need to prevent placement in certain worlds

Hey guys
I run a prison server and need a little help
I want players to be able to place saplings on their plots, but no-where else

So I could enable them in the plotworld, but disable them in every other world..

I'm just not sure how to do that

I know there is a blacklist option in essentials, but I'm not sure how to make it per world
Any help?

Thanks guys! x

 

Anyone :/