I saw a post on a local garden forum asking for volunteer opportunities for gardeners. Just in case one of your resolutions for the New Year is to do a little volunteering, here are some sources for local volunteer opportunities.
Volunteer Opportunities - from the Virginia Cooperative Extension Site.
City Blossoms - Help create urban gardening experiences for children and communities.
United States Botanic Garden - Opportunities are available weekdays or weekends in horticulture, education, and behind-the-scenes activities
University of Maryland Native Garden - help maintain garden, run plant sales, etc.
Search results from Volunteer.org - keyword garden, location Washington, DC
Search results from VolunteerMatch.org - keyword garden, location Washington, DC
Become a Master Gardener - University of Maryland Extension, Virginia Master Gardener Program