A conservative approach to harvesting is always a good thing. I harvest 3 fiddleheads per large established crown and have never had any problems (the crowns are as big as my fist). The average size of the fiddleheads is about the size of a half-dollar. I have hundreds of ferns so I basically get as big a harvest as I want and I cherry-pick only the premium fiddleheads. I also rotate from which colonies and crowns I harvest as well. Not necessary but as a result it never looks like I am harvesting anything and none of the ferns endure stress from possible overharvesting. I also am lucky to be able to trade fiddleheads for morel mushrooms from my morel-hunting neighbors.

A real treat is when you have a colony big enough to be able to go in and sneak some baby fiddleheads from some of the small new crowns. They are around the size of a nickel and they are very tender and delicious.

IMO it would be better to allow your fern to establish itself and start to spread out before harvesting. When you see others start popping up around the original, then I would consider starting to take harvests from the original crown. And if it turns out you really enjoy the fiddleheads, you are going to need a lot more ferns. :-)

Good Luck!
-Tom

Thanks! That's all very helpful info.

The bad news is, I went outside last week and noticed that the fiddleheads had all started unfurling, so I missed my harvest again this year.

The good news is, my fern has established itself! I noticed around 4 new plants popped up around it. I need to get out there and take a closer look, but it is definitely an official colony now.

So finally, next year I should get to taste some!