many people myself included tend to start feeding when the plants are around 2 to 3 weeks old and we usually start off with 1/4 of the recomended dose eg if the bottle says put 8ml of food in for every litre of water start off with 2ml. and double up each week until your at the maximum. personally i fill a 10 litre bucket with water and add all my nutes to it then give the plants 1litre each, sit back for a minute and let it soak in , give them another litre each, sit back again, and repeat until a small amount comes out the arse of the pot, this leakages is called 'run-off' and a lot of people say you should be looking for about 10% run off. at this point you probably wont know just exactly how much liquid your plant pot is gonna hold....just a trial and error job ....lotta people like to check the PH of there run-off as well....i dont bother my arse coz im in scotland and our waters probably the best in the world( thats why we make the worlds greatest whiskey).
