My plants are unhealthy no matter what I do! I've upgraded to the secon…

My plants are unhealthy no matter what I do!
I've upgraded to the second set of soil (blue) and the third set of water (yellow) but still a lot of the 2nd tier seeds I have end up nearly dead (down to the H) by the time they're fully grown. I'm not pruning anything except for the dead stuff, I keep them with plenty of water (usually at the bottom of the A) and I take care of infestations as soon as they happen. What am I doing wrong? How can I fix it?
If the tier 2 seeds wont thrive with the 2nd soil and 3rd water I have a hard time believing I can raise tier 3 plants will the 3rd soil and water, and I can forget about tier 4 plants.
Even some of my tier 1 seeds have trouble growing with the 2nd soil and 3rd water!