The micro climate on the roof is very desert-like; hot, dry and windy. The vegetable plants go through water much faster than if they were at ground level. I water the containers everyday, but the cherry tomato plant and the eggplants exhaust their water supply before I make it home. By the time I get back from work their 1 gallon reservoirs are empty and their soil almost bone dry. I really, really don't want to water twice a day, so I had think of a way of extending their water supply.
I was on the verge of buying one of those plant sitters with the ceramic cones, but I decided to try Mr. Brown Thumb's pop bottle drip irrigation system first. I'm happy to say it's working wonderfully. With them in place I can go a whopping 24 hours without watering!
Just poke a few holes in the bottom of the bottle, add some rocks to weigh the bottle down and place it in your planter. To make sure there is good contact between the bottom of the bottle and the soil press the bottle a few inches into the soil.
As a bonus I had all the required items on hand so it cost zero dollars. Anyone looking for a low cost, slow release watering system for their container garden can't do better than this, give it a try.