There are so many lovely spring plant sales in the DC-area:
Native Plant Sale, US National Arboretum, March 25
Garden Party & Spring Sale, Community Forklift, April 1 & 2
American Horticultural Society Spring Garden Market, River Farm, April 21 & 22
Plant and Herb Sale, Franciscan Monastery, April 22 & 23
Garden Fair and Plant Sale, US National Arboretum, April 28 & 29
Spring Garden Day, Green Spring Gardens, May 20
Bonus: DeBaggio's Herb Farm opens for the season on March 31.