I would like a plant that could be mulched, either as a verb or as a process say, in the cauldron. The resulting Mulch when applied to plots, Crop or Herb, would result in a higher yield.
Guano requires something fed to the batterfly but mulching could be an energy drain, and require a lot of energy to be spent to produce the mulch
The plant could be a tree or bush that can be planted in a patch or a dark patch or even a new type of type of patch (arid?)