It's amazing what you can learn about growing herbs just by doing a little reading. That's something I didn't do in my first year of growing basil but this year - because I want lots more pesto - I'm doing my (belated) homework.
How to Grow and Harvest Basil
My first big discovery upon hitting the old Google machine is that I shouldn't be letting it flower like I did last year. Not only can it give up the ghost foliage-wise after it's flowered, but most sources say that the leaves you harvest after flowering are bitter.
Turns out one plant should be yielding 12 or more cups of the stuff over the season - if you grow it right. And apparently that means: water, water, water - as often as daily. Next, before it sets flower we're supposed to: harvest, harvest, harvest - by removing as much as one-third of the plant at one time, then letting it recover.
Of course, my four basil plants, all harvested at once, yield more than I can consume all at once, but there's a fix for that - the freezer! This bag won't last long there, though - pesto's on its way.
Fungal Disease has Arrived
Unfortunately, the big basil news this season is bad news - the arrival of Downy Mildew to our shores, including right here in Maryland. If we see the symptoms - yellow bands and tiny gray specs - it's okay to just remove the infected leaves and even eat them - they're not toxic to humans - and the plant will presumably then keep on going. So the harm done by Downy Mildew seems to be primarily to growers, less so to us homeowners who don't mind imperfect-looking herbs.
For people trying to get rid of Downy Mildew, organic treatments aren't terribly effective, so prevention is advised. Prevention means giving each plant adequate sun and good air circulation - standard prevention for all fungal diseases. Also, though most basils are affected, pepper and spice basils are not (so far).