Soggy Gardens are a worldgen block that has a chance to drop a few of the listed items when broken. They are stackable items. They spread over time in a manner similar to mushrooms in vanilla Minecraft.
Soggy Gardens are found in colder biomes such as taigas and swamps.
Gardens are now picked up and transplanted by clicking on them while crouching and then dirt or grass. They can be havested by breaking the garden to obtain the garden items.
These drops can be changed in the config file for the mod.