Dr Doctor, I have bought a polytunnel and have filled it full of Roses. Have I over filled it because I have quite a bit of mildew and the roots have had plenty of water, the vents have been open for air circulation. Could it be cold nights. I am new to this and I am quite puzzled by it all, and don't know how to get rid of it. Michael, Llwynypia

Michael, if your polytunnel only had ventilation on one end, it is almost certainly too hot in there on sunny days. You need a through flow of air. The problem in tunnels is there are no roof vents, therefore heat rises and can't get out. It is an absolute MUST that there is a big opening on both ends so a through movement of air can flow through. Give a spray with Systhane to prevent the mildew getting any worse. These tunnel manufactures think that netting low down is the solution but they are badly misguided. Ask Albert Einstein, hot air rises, and you have to have somewhere for it to get out. Oh I forgot Albert Einstein has passed away, so you can't ask him. Take my word for it! Doctor Rose