@Vicktorious09

Yup, you aren't doing anything wrong! As long as plants are kept watered, they'll grow. Some just take forever. xP

Evolvulus plants have 24-hour growth intervals, while Pixpepper plants have 69-hour (눈_눈;) growth intervals. With the 5% growth fertilizer, that's reduced to about 65 hours. And you guessed correctly, the grade doesn't affect the growth rate. Plant grades mainly affect the potions you make.

If you're ever curious how long a plant will take to reach the next stage, you can search the Wiki for the seed name.

Please let me know if anything I said was confusing or if you have further questions!