It is very easy to fry your plants with foliar sprays, esspecially when using a HID light. If the water collects on the leaves enough it can magnify the power of the light, in affect boiling the part of leaf where the water magnified the light. This can happen very easily, even with just one spraying. This is just one grower's opinion, but I wouldn't recommend using foliar sprays. If you want the best results out of your plants you should go to a hydroponics gardening store and get some Dutchmaster or Fox Farm ferts, these two are both very popular and effective, and still pretty cheap as well. Just follow the directions on the bottle and you'll be ok.
Insane is right, I would like to add one thing. I foiliare spry once a week, because I got a feel for my girls. but the next day after fertin there leaves it is critical (in my experience) to spray them with good spring water the next day. NOT TAP WATER. Distilled is even better for rinsing the plant after ferting the leaves. Distilled has nothing in it. It is just pure water.
"IMHO"...[Buds, flowering plants shouldn't be sprayed at all. It could promote rot or mold, not to mention the residual raw nutes left to smoke.
Though an occasional 'misting' during veg will clean the pores and allows for better breathing, the only time that I "foliar feed", is if there is an uptake problwm through the roots.
If you are providing the rootspace, proper nutes and environment, foiliar feeding is uneccessary.
I'm with Hick.
The only time I foliar feed is if I have a deficiancey(sp) that needs quick fixing.
Occasionally I spray insecticide on my plants, and always go back the next day and spray with plain water.
Distilled water I suppose would be best because it has no salts or minerals to leave a residue, but with my indoor plants at least they are only alive for 3 months so I don't worry about it; I spray with spring water.