I think it would be awesome to have growing grass and even have it grow up to tall grass then if left alone eventually a wild wheat
Perhaps a basic seasonal pass on grass/tallgrass/shrub/sapling/tree growth?
If we make it anywhere close to fungal growth it would be WAY too fast (in addition to probably murdering everyone’s turn rate with constant checks.) However, it would be interesting to form the basis of nature herself retaking what man once made.
Mosses, vines and small trees would eventually envelope and tear open most structures.
The check probably won’t happen regularly, but on the map load.