honu--what you describe with Osmocote is a very common complaint in the nursery industry. I heard more than one orchid lecturor mention the weather-related 'release' of fertilizer with Osmocote.
They usually then recommend nutri-cote which is sold as Dynamite for the homeowner at places like Home Depot. It is more expensive but lasts longer.
http://www.arystalifescience.com/def...?V_DOC_ID=1601
Suze, I don't use time-release fert. at all in containers though I know it works well for many people (combined with other fert.) and is probably the easiest to use for beginners.