Lots of green events every spring in Baltimore... watch for these and similar events next year too:
This Saturday is the Baltimore County compost bin and rain barrel sale: take advantage of the great discounts! http://www.baltimorecountymd.gov/News/releases/0420barrellbinsale.html
Check the Baltimore Green Works event calendar http://baltimoregreenworks.com/events/calendar/
Herring Run Watershed Association http://baywatersheds.org/ native plant sales, rain barrel workshops, etc.
Our local chapter of the US Green Building Council (USGBC) http://www.usgbcbalt.org/
Feeling the urge to bike around Baltimore? Here's a map of bike lanes and trails from CityPaper...