I hesitated to say anything about this topic because we are in such different zones. In my hot zone I use plastic because it holds the moisture better than anything else. In the summer I need to water my potted roses (miniatures) everyday. I can't afford to lose water through the pot. You are lucky if the wine barrels work for you. Here it is a matter of being practical. Not to mention that wine barrels are not availible here like they are to you. A thought occured to me...do you line the barrels with plastic?