Timing hay harvest can be about as much art as science, but Bill Wilson, who makes hay on his farm near Little River, Texas, says the key is relative humidity.

“I have noticed a number of balers, or rakes in the hay field when the hay is way too dry,” he says. “In that situation, farmers are losing most of the leaves.”

And the leaves make up the bulk of the hay, he says. “About half of the hay will be leaves. Lose your leaves and lose close to half your hay.

“Also, roughly 66 percent of the nutrition is in the leaves. It is not hard to start out with 2 tons per acre of 12 percent protein coastal hay and end up with 1.25 tons of 8 percent protein hay.”

Wilson says the trick is to kick leaves around when there is enough moisture in the leaf to keep it from shattering. “The usual school solution has been to rake before the hay dries to below 40 percent moisture. As far as it goes, this is true. The key is to have the humidity inside the windrow at roughly 70 percent. How you get there is up to you.

“The ideal time to rake hay,” he says, “is when the free air relative humidity is above 70 percent. Often that means first light in the morning.”

The same general rule applies for baling. “For daylight baling start as the humidity goes below 70 percent. As humidity approaches 50 percent moisture on the outside of the windrow hay can become dry enough to shatter leaves, while the leaves on the bottom are tough enough to hold together. Baling at night is nice if your climate will allow. Then the leaves start to toughen up before the stems and the outside before the bottom.

“We used to go to the field when the air felt right. That is above 50 percent relative humidity. Better yet is to be close to 65 percent relative humidity. It's not hard to tell when it is right; the leaves stop shattering. Just start raking right after your noon nap and start baling after you finish raking. This same principle works for alfalfa and sorghums.”

Wilson offers a rule of thumb for harvesting hay:

Rake when it is too damp to bale.

Bale when it is too damp to combine.

Mow when it is just right to combine.

“I have no references,” Wilson says, “as most of (what I know) I learned from oral communications. The rest I picked up from reading anything I can find on baling hay.”