Gardening classes are offered all around the area: at nurseries, community colleges, community gardens and certainly through the Oregon State University Extension Service. I'll provide links to some, and you will find more with an internet search such as "gardening classes Portland Oregon".
At the OSU Extension Master Gardener Metro Area home page you'll find links to training information, an events calendar, and county chapter pages (along the right side): http://extension.oregonstate.edu/mg/metro/.
The Clackamas MG page includes locations for 10-minute University presentations and regular meeting lectures the public is welcome to attend: http://www.clackamascountymastergardeners.org/
The Learning Gardens Laboratory is another option: http://extension.oregonstate.edu/mg/metro/lgl-0
In September registration opens for the Master Gardener Training: http://extension.oregonstate.edu/mg/metro/2015-MG-Program
The OSU Extension Gardening home page includes a nearly overwhelming amount of information and links to yet more. Check it out: the calendar and some of the articles change seasonally, so it is a page worth bookmarking to return to regularly: http://extension.oregonstate.edu/gardening/
Best wishes with your plants.