Cool picture. Where was it taken? It's so interesting to me that weeds are able to grow through concrete, asphalt, and pavement. It seems to me that, when that happens, it's time to fix the paving job. I would recommend calling a professional. They'll be able to fix it so that other weeds aren't able to push through. http://www.mancusopaving.com/asphalt_paving_toronto.html