There are many diseases that affect plants which can linger in the soil for months, often whole growing seasons, waiting to strike when the plant re-appears in the bed. Many people rotate the crops in their veggie garden so that diseases don't have somewhere they can permanently live, with a steady supply of a particular plant. But with a smaller plot that is not always an option. And that's where frost can become a gardener's best friend.
If you have an empty bed during a spate of cold, frosty weather, rather than covering it up, leave it exposed to the elements. If you have a frost, it will freeze the surface, and, depending on the temperature, likely penetrate deeper into the soil. This will kill off any bad microbes or fungus within the area that the frost affected. The next day if you can, turn the soil so that deep-down earth is exposed, allowing another frost to kill any diseases left that had been protected. Exposing the bed to frost, even if it doesn't destroy all disease, should help in eliminating any problems. The great thing about it is, you need to put in little effort, and in most cases, come out of it with a positive outcome.