I put a white sheet round it to reduce photosynthesis, but doesn't cover the top and is probably to thin to completely stop it. Anyway it's the first time for 2 years and was ready. Red mildew in it! Hasn't affected the cleaning results, but it was a tad yucky to say the least! Hopefully I'll have it covered with wood for frost protection soon, time will tell if it will still go manky!