"Dano" writes:

Now, everyone, please. Shingles are a fantastically bad idea. I hope no
one is considering this idea. Fer chrissake, stop this madness.

There's a reason why old shingles are supposed to be disposed of as
hazardous waste.

(Don't a few old types contain asbestos?)

There are several kinds of plastic mulch commercially available without
unnecessary risks.