i flush, everytime i water
what??? seriously I do.
just not as thoroughly as I would if i was flushing at the end of the flower cycle.
this means when you water, you water untill you have mostly clear runoff.
your plants shouldnt need anything but light for 5-7 days after that.
if you fuckup and try feeding or watering during that stage after a flush/watering it leaves the soil saturated with moisture that is not moving
this moisture then becomes anaerobic, that is, all of the dissolved oxygen it the water is used up by either the plant, or microrganisms (mainly bacteria) in the soil.
this standing anaerobic water is an almost perfect medium for fungus to thrive, so your roots rot.
the standing anaerobic water also will release and absorb nutes (salts) from the soil, which means a very high ppm of dissolved solids... which in turn will wick moisture out of the plant to balance the ppm gradient, as i stated before.
so you can see that finding the optimum time to feed is more of a fine art than simply following the directions on the bottle.
i typically feed 5 days after a watering. and when i feed (mebbe you guessed it) i pour untill i have runoff. that way i know the nutes are going through all of the soil and are not just piling up in the upper level of the pot. this will also encourage the roots to grow, as nutes are depleted in one part of the soil, adventageous roots will spread to the rest of the pot.
rootbound plants are a myth.
rootbound = improperly fed plant. the plant doesnt get enough nutes, so the roots grow, looking for more nutes in the soil. sometimes they will even push a plant right out of the container! this tight rootball prevents the flow of water through the medium... which makes the water anaerobic.... you starting to see a pattern yet?
the type/ strength of the feeding depends on what stage of growth im @.
i use a weak 5-1-1 for veg, and 10-20-10 for flowering, sometimes, and very rarely, i will feed 20-20-20 if it looks like i have some heavy defs going on.
i also use heavily ammended soil (aka hotsoil) to pretty much keep the fertilizing to a minimum.
with soil, that is the key to success. minimal nutes.... its too hard to control heavy feeding... ph issues, ppm issues, it gets complicated rapidly. K.I.S.S.
over fertilizing/feeding is probably the most common mistake i see on here, besides over watering.