The most economical time to buy hay is in the summer, during and right after the growing season, because prices will go up later in the year, as the supply dwindles. But if you stock up on hay, you'll need to store it carefully. Otherwise, it may lose nutrients, grow mold, ferment, or even spontaneously burst into flames.
Dampness and poor air circulation are the culprits. Moisture causes hay to grow mold and ferment. Fermentation produces heat-and heat can build up to the point of combustion.
Start dry. Buy only properly cured hay, so it's dry from the start. Open a few bales, and stick your hand into the center of them. Reject hay that feels damp, or warm and steamy. Also reject dark or musty-smelling hay, which may be moldy.
Go undercover. Store your hay underneath a roof, where it's protected from rain and other elements. Although a hayloft is convenient, it's better to store your hay in a separate hay barn or shed. Hay is dusty-which can harm your horse's respiratory system-and it carries that risk of spontaneous combustion.
Ventilate. Make sure your storage area has good air circulation, with roof vents and/or cupolas. Also consider installing a fan. To prevent heat buildup, look for one that kicks on automatically when the temperature inside your storage area hits a certain point.
Stack loosely. Also to prevent heat buildup, stack bales so that air can flow between them, rather than tightly against each other. Never stack hay against walls or all the way to the ceiling, as solid barriers block airflow. Also, set bales on their sides, so the stalks run vertically. This helps warm, moist air rise out of the stack.
Keep it up. If you store your hay at ground level, put the bottom bales on wooden pallets-rather than on the ground (or even on a concrete floor). Pallets let air circulate, so the hay absorbs less moisture from below.
Check and recheck. From time to time, break open random bales to check for signs of mold or increasing heat. If a bale feels hot inside, take it out of the barn and break it apart. You'll probably need to discard this fermenting bale, as mold will already be starting to grow.