Plant lots of plants
I've not noticed you get more from one type of plant or another, tbh. I grow orange petals for the guild, 600 plants at a time across 6 chars. A backpack with 100 plants in on each one, an empty backpack to tend them into and a central container with potions and jugs next to a water trough. It's time consuming, and can be a little fiddly til you get the hang of it, but yes, it's fun