Vienna Farmers' Market
Do more vendors attend the Vienna Farmers' Market over the course of the year? I went there on the first day of the season and there were maybe 3 vegetable vendors there. I've been going to Dupont Circle since then but if I can save the trip, I will !
You might try the Falls Church Farmers' Market, Saturdays 8-12 all year round. It's a lot closer than Dupont!
Reston's has grown in size steadily over the weeks. Finally someone with local honey showed up this past Saturday.
There are certainly others closer than DuPont, though. Frying Pan Park might be a good one for you - it's on Wednesdays.
I would suggest the Arlington Farmers Market. There are several veggie vendors to choose from, and a bit closer than dupont.