shake that thing
The first thing about ferns is they shake. Breathe on them and they shake.
The second thing about ferns is they grow in wet, dark places.
So try to photograph a fern and you'll find that because of the first thing about ferns, you have to have a short exposure to catch them when they're not moving, and because of the second thing about ferns, you have to have a long exposure to get enough light onto your film.
What does this mean for someone who is trying to take a photograph of a fern? It means that shot after shot, five or ten or fifteen seconds into the exposure, one of those twenty-nine fern fronds, usually the same one over and over, starts to shimmy like your sister Kate. So you sit and wait again for whatever whisper of a breeze there is to die down, and for the frond to stop shaking, and now you notice you've got to go from a twenty to a thirty second exposure because it's getting later and the light is fading. So you decide to risk a wider aperture hoping you've still got enough depth of field to hold everything in focus, and try the whole thing over again. Until finally it's useless to go on, and you hope among all those shots of a perfectly exposed, perfectly focused group of ferns with one lousy blurry frond, there'll be one where everything was still enough for long enough to make a decent shot.