Fertile Soil treats the targeted Farming patch with supercompost and 18 farming experience is granted. Supercompost is not needed and the spell can be cast even after the farming patch has something growing in it; however once the plants have fully grown, the spell can no longer be cast, and players will instead receive the message, "Composting it isn't going to make it get any bigger." As with all Lunar Spells, the quest Lunar Diplomacy must be completed to cast this spell. It is strongly suggested to use an earth staff when casting the spell. If you use the spell on anything but a farming patch, your character will say "Um...I don't want to fertilise that!"
This spell cannot be cast on the jade vine patch. Horacio will say "Oi! Don't you be fiddling with Magic in my garden! I'm an organic gardener, me!" The spell also cannot be cast on the Crystal tree patch in Prifddinas. Attempting to cast the spell on the patch yields a text message saying "Um, I don't want to fertilise that."
Attempting to cast this on a compost bin will yield the following message "No, that would be silly."
Casting Fertile Soil on a farming patch near Seers' Village is one of the Seers' Village Elite Tasks.
This spell is more expensive than a bucket of supercompost by 1997 coins, assuming the caster is wielding an earth, lava, or mud staff.