Are you sure what you found are black trumpets (Craterellus cornucopioides/ C. fallax)??
I've never heard of them growing before the middle of summer.
The somewhat similar looking "devils urn" (Urnula craterium) are extremely common this time of year.
Black trumpets would be growing terrestrially (from the ground), Devil's urn would grow from wood.
From wiki:
This species is often listed in field guides as inedible, or not recommended for consumption due to its tough texture. Michael Kuo, in his 2007 book on edible mushrooms, lists the taste as "mediocre", and comments "the devil's urn is not as bad as I thought it was going to be. It's not good, mind you, but it would be possible to eat it with a forced smile if your Aunt Wanda served it to you."