Dog has suddenly begun eating houseplants, regurgitating them in the night

I realize it's a normal part of a dog's digestive process to eat grass and plant matter and regurgitate them if need be, but my 8 year old mixed breed has lately begun eating the stems and leaves of houseplants and throwing them up. Apparently he does this at night when everyone is asleep and no one can take him out to graze. Is there cause to be concerned yet? Otherwise, I haven't noticed any significant changes in mood or behavior. The only other health problem he's had recently is a persistent sore on his front leg which I can't imagine could be related. Any advice appreciated.