Though there is no "garden" snake with that official common name, those snakes most commonly found in gardens are not venomous. Though they can and do bite, there is nothing toxic about it.
The most common snake referred to as a "garden" snake is in fact known as the garter snake. Though there are several varieties, they are easily identified by the solid light yellow stripe or stripes which run down their back. Care should still be used around any snake found in your yard, as even nonvenomous snakes are known to carry a heavy dose of bacteria in their saliva, which may not be as immediately lethal as the venom of a rattlesnake or water moccasin but can lead to a very serious Staph infection.