Make big pheromones efficiently. That is all.
Heal by merge works in small puzzles. Only. Unless I am missing something, even a 80+ merge does not heal for any noticeable amount.
Big post coming up that explains more. Your upgrades are insufficient I guess. You need top tier pheromone maker. That is biggest tree or biggest seedling. I have yet no idea how long it would take to upgrade a candle to match the Ancient Ent's Leek or the Tangled Factory. Or if there are any other mechanics I am missing. With those two you can start your pheromone grind with Big Pheromones (lvl 4). It takes "only" about a hundred of those under optimal conditions to merge5 the biggest pheromone. So my guess, less than an hour for lvl 9 pheromone. Took me maybe 10-20 lvl 9 pheromones for all healing. Can't remember and I pull-heald alot. And all the healing I grinded in the beginning with click healing of the seedling bed and couch pales besides 1 of those lvl 9 pheromones.