Farmers who make dry hay face problems in field drying most every season. In some seasons, it is extremely challenging to make dry hay. Frequent showers, constant cloudiness and wet field conditions increase the risk of putting up hay that is not dry enough to cure well in the barn.
Spontaneous combustion is a real problem for hay producers and buyers. To prevent fires in the haymow, it is important to know the weather conditions under which the hay was made, especially if it is hay you are purchasing and did not make yourself. Stacking small, rectangular bales at 20% moisture or higher, and large or round bales at 16% moisture or more, potentially creates the conditions for a fire. Fires in freshly cut hay usually occur within the first two to six weeks after baling.
How to Tell if You Have a Problem
Some heating in new hay is normal. The quickest way to tell if you have a problem is to drive a long pipe (8-10 ft., 3/8-inch diameter) or an iron or copper rod into the center of the stack. Leave it in for 20 minutes and then pull it out. If it’s too hot to hold in your hand, the hot hay should be removed immediately. Another warning sign is that smoldering hay gives off a strong, pungent odor. If you suspect you have a problem for any reason, monitor the temperature of the haystack. A temperature of 150°F or higher means that hay is entering the danger zone. The following table provides guidance for actions to take depending on the temperature of the hay.
Hay Temperature Course of Action Guide
120°F or Below
No concern and no action needed.
120 to 140°F
Check temperature daily.
140 to 150°F
Check temperature twice a day.
Entering the danger zone. Check temperature every two hours.
150 to 160°F
Begin moving hay out of the structure. At a minimum, stacked hay should be disassembled to allow more air to move around heated bales to cool them.
160 to 175°F
Call fire department; have them on-site before moving hay.
The danger of spontaneous combustion is rapidly increasing. Hot spots or fire pockets are likely. If possible, stop all air movement around hay. Call 911 to alert of a possible hay fire.
Remove hot hay. This should be done with the assistance of the fire service. Fire service should be prepared for hay to burst into flame when it contacts fresh air. Move hay away from buildings with bucket-loader or bulldozer.
200°F or Higher
Hay is almost sure to ignite. Remove hot hay. This should be done with the assistance of the fire service. Fire service should be prepared for hay to burst into flame when it contacts fresh air. Move hay away from buildings with bucket-loader or bulldozer.
Provided by Cornell University Cooperative Extension.
Cattle who stand close together in low ground, and feed hard together, are said to be foretelling rain, but if they stand on high ground the weather will be fair.