The Dungeon Growths patch, written by Pasi Kallinen, adds code that enables plant life of various forms to grow and spread in the dungeon. It has been incorporated into SLASH'EM, SlashTHEM, UnNetHack, and Hack'EM.
The patch contains three major elements: herb growth, tree growth, and tree drops.
The patch considers certain plant-based items to be herbs. When left on an appropriate tile for a long time, these items have a chance of multiplying.
Land herbs multiply when left on the floor:
Water herbs multiply while underwater:
Trees in the dungeon can potentially seed trees to nearby squares. While this growth is slow, it can mean that unattended trees can become dense forests by the time levels are revisited in the ascension run.
An additional effect is that trees can spontaneously drop ripe fruits from time-to-time. This is quite rare, but unlike the tree seeding it can happen when you are in direct view of a tree. The fruit that is dropped is random and will only be a single fruit. There is a following 5 in 6 chance that the tree will be marked as "looted" and will not drop any further fruits. It is extremely fortuitous if you ever see the same tree drop two different fruits, as it is possible but very improbable.