Every summer I struggle with fluctuating relative humidity levels among my humidors. Sometimes, even without a passive humidifier, my levels can approach 72-75%. Rather than leave the lid of a humidor open in an effort to decrease the humidity I’ve come upon this neat little trick.
Cigars are frequently separated within a box by layers of thin cedar or accompanied in the box by a cedar spacer. Rather than discard these odd hunks and sheets you can re-use them. Keep your cedar at room temperature and ambient room humidity (which is hopefully lower than in your humidor).
When the humidity in your humidor creeps up to levels higher than you prefer, simply add a sheet of cedar on top of the upper layer of cigars or tuck a cedar spacer into an open area of your humidor. Cedar, like tobacco leaves, is hygroscopic, meaning it absorbs water. This is one of the reasons Spanish cedar and cigars have been bedfellows for centuries. As the humidity increases, the cedar absorbs the excess moisture, almost preferentially, before the tobacco. It also contributes slightly to the aroma of the cigar.
After a day re-check the humidity in your humidor and if it has not decreased to the level you prefer, remove the cedar and replace it with a new, dry piece. Continue this until you achieve your desired relative humidity.