I've just harvested a tier (top) of EMPs and decided to purchase the 300k gold Plant All utility spell from Avalon.
I planted one EMP on an empty plot and proceeded to use the Plant All spell on it. The tool tip indicator turned into a Green Tick, so I clicked to cast the spell, much to my dismay, I received the message "No matching soil found".
There were clearly matching empty medium plots as I had just finished harvesting the other EMPs earlier. Am I doing anything incorrectly? (I'm suspecting it's because the middle and lower tier still had plants on them, is this the case?)
Yes it's because the lower levels have plants. Stacked gardens need to be planted from top to bottom. The plant all spell works great when you have clear plots. I regularly plant 1 EMP then use Plant All to do the other 68. You should really stick to one type of plant in stacked gardens so they all finish at the same time.