harry wrote:

Even dew will spoil hay.
The black bags are not hay but silage. (Fermented grass)
Silage BTW would be twice the weight of hay.
http://en.wikipedia.org/wiki/Silage

Hmm. When I visited the UK contryside, I saw many houses roofed with straw.
From my reading, a thatched roof can last up to fifty years. And there are
buildings in existence that were originally thatched 500 years ago, with up
to seven feet of additional thatching implaced over the years.

Perhaps you should get out more.