I planted three Japanese ferns this year and two of them have developed brown spots on their fronds. Is this sunburn?

Certainly looks like it. Are they in a spot where they get direct sun?

That browning could be something left over from the nursery you got them from. im more inclined to think its a disease/fungal issue. we have several Japanese ferns that have the same, or very similar looking brown patches, always get a little bit each year, and they're in deep full shade. I wouldn't get too worried about it just yet, since you just planted them. give them until next year to unfurl new fronds, than take it from there. unless you do in fact have them in full sun...

Thanks very much. They do get some afternoon sun. I'm going to let them stay put for now and see what happens. Thanks again.