SUPPOSEDLY, all ferns all are edible, but the only confirmed one that is recommended is the Ostrich fern, as some ferns are believed to potentially contain carcinogens (though what doesn't just about nowadays? Even water does I swear...)
Don't start noshing on your dentist's office fern just yet (plus they might use some nasty stuff on it), but you might be surprised to hear that the fiddleheads of Ostrich ferns are quite delicious and similar to that of asparagus in flavor with a little steam and butter.
Ostrich ferns are quite common, I've seen them sold in pots at my local grocery store and can tolerate considerable temperatures, naturalized in the New England areas, tolerating zones 3-7. I grow its relative the Royal/Osmanthus/Interrupted fern which is purportedly edible too, though I have yet to try it due to its smallness in size.
(Osmanthus fern, too small and w/no fiddleheads!)
Though I do not grow Ostrich ferns myself due to lack of room some inability to provide good shady/moist conditions with room for a potentially 3-5ft plant, I hope some day to be able to do so and if others can provide a place for them in their yards to naturalize I would suggest it in the name of tasty and an easy conservation kind harvest rather than creating a potential over harvesting issue in its natural wild environment as harvesting and eating fiddleheads is starting to become somewhat trendy.
You need good conditions and plenty of shade of course if you want them to do well, and also it takes a good while before the fiddleheads are of a good size before they make good eating in volume. Think of them as really pretty asparagus (which take at least 3 years before good establishment).
It's also good to note too that you can't just take every fiddlehead from a plant because, like asparagus (and I suppose nearly every perennial vegetable you want to come back), it's called photosynthesis, they need it to grow and continue on with that beautiful thing called life to nourish you next year (ok, they probably don't care about your needs, but I assume you care about theirs).
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