As it has been said by others Seed Storage would be great. Not necessarily in the Seed screen. Maybe there can be some sort of storehouse that seeds can be kept in when you are not using or wanting to use them right away.
The additional speed choices would be nice because while I do understand that it is possible to buy things to help speed up the growing process they growing rate isn't constant. (When you use the vapor bomb it doesn't effect all the plants the same way so it can become quite expensive very easily and quickly.)
Some way to keep track of the plants as suggested by Gamemastr1 would be great. I want to be able to figure things out myself and because of that reason I did decide to start keeping a written record of everything, but there has to be an easier way that is built into the game.
Different ways to trim the plants would be nice too. (I like the idea of putting a plant on a turning table to move it around to look at it from all angles that Funkiroller suggested.)
I know that I am repeating things that other people have already said repeatedly, but so far in my experience these are things that have been a source of frustration for me.