If the plantings in your yard possess any significant degree of diversity, there's a good chance that you're growing poisonous plants -- without even knowing it. You'd be surprised at how many of the most common landscape plants and native volunteers contain at least some parts (leaves, berries, etc.) that are toxic. Personally, this doesn't worry me, as I rarely feel the temptation to nibble on my plants as I stroll through my yard. However, if you have small children, pets, or an uncontrollable appetite, it behooves you to learn more about poisonous plants. And of course, there's always good old poison ivy, the mere touching of which will cause you to be sorry for days!