Rock gardens are easy.
;-)
If you want easy, it's hard to beat ivy. It's pretty hard to kill. (But I hate ivy myself. Too many people treat it as a maintenance free ground cover, but it's very invasive and will help to kill trees that it crawls on. (Trees shouldn't have their bark wet too long - ivy keeps tree bark wet, attracts ants and other bugs, etc.).) Please don't go there unless you can't grow anything else. :-)
Small [link|http://www.waysidegardens.com/webapp/wcs/stores/servlet/StoreCatalogDisplay?storeId=10151&catalogId=10151&langId=-1&mainPage=advsearchresults&SearchText=p16.v227;s1.Azalea&scChannel=Trees%20Shrubs%20AS|azaleas] might be a good choice for you. They enjoy shade and cool temperatures. If you keep them trimmed, they can grow well in containers. They can be very colorful and bloom a couple of times a year. You'll need to water it once or twice a week, and maybe trim it every other year, but that should be about it.
Cheers,
Scott.
