Wolfe considered how to best deal with their request. Garden Charms required a bit more upkeep than a power plant, as optimally you wanted to tweak them every growing season for the crops that you were planting.
Proper crop rotation lessened the burden on the spell, and produced the best results, but Wolfe didn't know much about it beyond the name of the technique.
"I can have the witches set it up for you, but you will need to send Fae around once a year to ensure that the spell is still properly calibrated for optimal growth. Well, either that or follow their crop rotation recommendations exactly so that everything stays in balance.
The charms are affordable at the lower ranks, and you're trying to grow on previously fertile fields, not on barren sand and clay, so it should be possible to do while I travel to do the power plants.