Tree Storage Coolers (continued)

• Maintaining and Monitoring Tree Coolers
• Temperature
• Humidity
• Hygrothermographs

Humidity

The relative humidity of the ambient air in the cooler is a concern only for long-term storage of unfrozen trees. Trees that are packaged by the nurseries will have good moisture barriers to maintain humidity inside the packaging. Even so, long-term storage of unfrozen trees requires relative humidities of 95% or higher. Otherwise moisture will slowly move out of the tree bags and boxes as moisture is removed by the refrigeration equipment. Hygrometers with digital readouts can be used to monitor humidity.

Several points should be kept in mind when measuring relative humidity. The cooler's initial capability should be checked when the storage facility is empty. Simply putting trees in a cooler can increase humidity because the trees produce moisture. High humidities in a cooler recently filled with trees does not ensure that the cooler is maintaining the humidity. A general, slow decline in humidity is an indication you are losing moisture and need to replace it. It is sometimes a good idea to keep the cooler floors covered with wet sawdust when the cooler is operating at temperatures above freezing.

Hygrothermographs

Hygrothermographs are often used at districts to record temperature and humidity over time. These instruments are only as good as their maintenance. After the first year, they must be recalibrated and maintained or their readings can be erroneous.