The quality of my plants are ALL over the place. They change all the time. At first I thought it was based on my house's eco footprint but I dont think thats it. They started off normal...then shot up to perfect...then back to nice...etc etc. Most of the time I cant evolve them but every now and then I can. Its just crazy time in my yard lol.
Mine started as normal, but the second I left the lot (load screen) and came back, they were perfect. Just moving a normal quality plant in build mode from one planter to another shot the quality up at least a level. Then I went on holiday for three days, came back, and a good number of them were back to just planted, so in my annoyance I cheated them back to mature. Funnily enough, some of those suddenly decided they were no longer perfect and I could evolve them as normal. I am mystified.
May have been coincidence, but the second I fabricated a hydroponic planter, placed it, and put plants in it (that in itself was glitchy), I seemingly no longer had to water
any plants, nor did I see weeds while I had it out. I eventually chucked it into household storage and things went back to normal, for a certain level of normal.
The only plants unaffected by the quality weirdness have been custom plants, but those (and vanilla plants) were affected by the growth stage thing.