[Cob] using hay instead of straw

[Kristen Davenport]

HI there
Most of the cob books and experts have said we should not use hay for building with cob, rather than straw, but I'm completely at a loss about WHY. I've received all kinds of different answers.... "It will sprout" (so what)... "It's not as strong" (huh??)

To me, none of this makes any sense.

For instance, in the Becky Bee book she says "Do not use hay. It decomposes." Yet a few sentences later she states, "If you're an ambitious purist,  you can gather your own grass stalks or experiment with other plant fibers." Well, HELLO, what do you think hay is? Grass stalks. Not to mention, as an avid composter, I can tell you that "straw" decomposes just the same as "hay"... and "hay" can mean anything from brittle stalks with seed heads to thick straps of wide grass to bales of weeds and wild rose stalks and willow branches..

Can anyone give me a reason that makes sense to me why we shouldn't just use my neighbor's weedy hay for building with cob?

Thanks.

Kristen