Lola,
Many use Dyna Gro Foliage Pro, you might want to look into it. It is pretty concentrated, so it is economical to use diluted often. Not organic, but probably one of the better inorganic fertilizers on the market IMO. I tend to also use Fish emulsion/liquid Kelp, or compost teas occasionally as well.
Spider mites, use Neem oil before they get out of control, spray religiously, they get worse as summer comes. I never seem to kill them all, but you can keep them in check. I noticed the Spider Mites, and Whiteflies a month earlier than usual even with our colder winter, the buggers are going crazy this year.
The post above with nutrient deficiencies is awesome.
Good Luck