I have some salad things started in a cold frame alongside my now dormant garden. Its just a simple box made from an old freezer, with a plastic cover. I'm noticing that the condensation which drips into the cold frame is causing excessive moisture to build up. The soil is now nearly muddy. Hopefully I'll have a few days this week to open it and allow it to dry a bit. But is there any way to prevent such a build up to begin with?