I have a few ferns with long pointed leaves, and their tips have turned brown. The plant is otherwise healthy, and is actively growing.
What is causing that? Should I worry about it?
In addition to those already given (insufficient humidity and very high ambient temperature), one of the most common causes of leaf-tip/ edge browning is an over-dry compost, resulting from:
*Where a peat-based potting compost has dried out completely, and has very often shrunk away from the sides of the pot; the water just runs through the gap and exits the pot without really wetting the compost. Many potting composts - particularly peat-based ones - are very difficult to wet, if they are allowed to dry out; surface watering is ineffective, and the best way to ensure that the compost is thoroughly wet, is to stand the pot in a bucket of water (to just below the rim) for an hour or so, and then drain it for a time to ensure that the plant is not sitting in water afterwards.