This is mostly for Carl and/or Pam to note in their Gardening guide, but this may apply to others as well; note that this requires Supernatural to achieve.
I found that when it says "Harvestables", it isn't kidding! I had a Witch conjure a LOT of apples, enough to get 20 of them excellent or higher (said witch is at level 10 Spellcasting skill and has Magic Hands) while drinking a handful of Essences of Magic midway through. The opportunity even recognised those apples as harvested, which seems a little odd.
It does require some effort and luck to do, but it's much quicker than planting some apple (or other plant) trees and waiting for them to grow.