If you're not yet convinced that sub-irrigation is the way to grow plants in containers, read the customer reviews (see link below) about these sub-irrigation conversion kits (erroneously called "self-watering").
It's convenient to buy them, but you can easily do it yourself using recycled materials. This is just one of many posts that shows how to do it. Also, look at Johanne Daoust's Flickr photos. She shows how she converted her entire rooftop garden, including round pots and raised beds.
via www.gardeners.com Click on the "Reviews" link at the top. It's right under the heading.