like casik said, only, use 3ltr bottles with a pin prick or 2 in it, and just lay it next to the stem. use green bottles or bury them in if you want them to be less noticable. just take 1 full 3 litr bottle down every 2,3,4 weeks to refill go quite regularly to start with, so you no how long it takes for a bottle to empty. that way you can work out how much you need to take, and how regularly you need to go refill. with only a couple of pin pricks it should take a while.
or just go when YOU think they will need watered, say, if it hasnt rained for 4,5 days. you will no how much moisture your soil will hold, how long it will take to drain, things that only you no.
take every 1 of these comments in, and use what you think is right 85CANNABLISS