Judy Thompson was walking Judy Graham and Ellen Levin through her Glen Burnie garden, explaining her gardening practices and showing off her plants.

"I try to plant close enough so that when they're large enough I don't have to do much mulching," Thompson said.

Graham and Levin were at Thompson's home to see if she was Bay-Wise certifiable. The certification, offered by the Maryland Master Gardener's program, rates several factors to evaluate how Chesapeake Bay-friendly a garden is.

In Anne Arundel County, 167 gardens have been certified Bay-Wise since 2001, 46 of them done last year, said Mike...