Okay, I understand the idea that there are different levels of plants, the first one can grow in plain soil with plain water, and then higher levels of supplies are needed to successfully grow the plants. What I can't find is a list of what plants are on which "tier."

Any help?

yes.

in THIS thread by LadyCFII in the guides section is THIS link to a .pdf file.

on the bottom of page 2 on the right, there is a box labelled "Tier Colors" .. these colors correspond to the colors of the names of the flowers and foliage in the charts in that same .pdf file.

Cheers,
-Borg

Borg, you're my hero! Thanks!