I don't know if this exists or not, I'm a moderate gardener, but what about a spell that makes your plants like each other? You know how Dandelions like Snapdragons (I believe, it been a while since I grew some Dandelions)? Maybe cast it on one plant and it likes the types around is for a certain amount of time?
I like all of the ideas. I actually would really really like that first idea Blessed Harvest to be an actual spell except that it would be more energy and exaggerate the fact that it can only be used on elder plants. As for the energy part, maybe 3-5 energy depending on the rank of the plant, other wise the spell might be too op. I really like the ideas though.