Help picking planting for damp shade
 

Hi, me and my partner are looking to tidy up a large area of mud roughly 9' x 12'. At the moment it is overcast by neighbouring trees and our house. It appears to be very damp, as there was a large thick moss growing on top of the mud.

We are looking for a way to fill the space on an EXTREMELY low budget, and perhaps improve the dampness? I considered planting mint as this would spread quickly?

Does anybody have any ideas on how to improve the soil and plants that will fill this type of environment quickly and cheaply?