Hay Storage Strategies for Safety & Savings

and cover with a secured tarp to reduce exposure to moisture and sunlight which bleaches hay reducing its nutritional content. The stack should be arranged in a pyramid shape to encourage moisture runoff. 
Stacking Schemes
Hay should be stacked on wooden pallets or tires to allow air to circulate underneath and reduce contact with any damp surfaces. The bottom layer of bales should be stacked on their sides with the twine facing sideways instead of upward. The unevenness of the surface promotes air circulation which reduces the chance of mold growth. Ideally a hay stack will have narrow gaps between rows of bales with alternate orientation of the bales in each layer and be no more than four or five bales high. A gap of at least 18 inches should be left between the hay stack and the walls and ceiling to allow adequate airflow and ensure that vents and air ducts remain unobstructed. 
Track Hay Temperature
Although the greatest risk occurs during the first two weeks after hay has been stored spontaneous combustion can remain a possibility for up to two months. Hay should be monitored daily for heat for at least two weeks longer if you suspect the hay was wet when baled. A tube thermometer available at many feed stores or compost thermometer can be used to check the temperature of the hay in the middle of the pile where heat buildup is most likely. A temperature reading of higher than 115 degrees Fahrenheit 46 degrees Celsius may be cause for concern. A metal pipe can also be inserted into the centre of the haystack and pulled out periodically to check for heat. A caramel odour andor visible steam emanating from the hay are obvious signs of danger and indicate that the fire department should be called immediately.