I have several large tree ferns that are dying. The leaves are turning brown, not one at a time, all together, and then dying. It seems to be spreading to other ferns in my yard. They have been here forever. I only water, and do not fertilize. Any ideas?
It's odd that the fronds are all dying back at once in mature tree ferns, so unless you've had extremely windy conditions that are unusual, or something drastic has changed in the environment, I suspect there's a wider problem. Knowing where you are in the world would have been useful, but two things spring to mind. The first is root rot - tree ferns do better if the soil around the top is allowed to dry out a little, and then the ferns are watered deeply. If you've had plenty of wet weather, it might be root rot. Symptoms are sudden die back, as you're describing, and sometimes, mushrooms or toadstools can be seen around the base of the tree or nearby in the soil. There is, unfortunately, no effective treatment once die back has occurred - the tree either recovers or it doesn't, though you could try watering in a fungicide at the base and fertlising the trees if you suspect this might the issue.
If you're in Australia, there is something new causing sudden dieback - the cause is not 100% certain, but it's suspected to be caused by infestation with scolypopa australis, or the Passionvine Hopper, which penetrates the trunk and sucks the sap, introducing an unknown pathogen causing sudden dieback and killing the tree. It's not clear whether this really is the disease vector though, because other countries are also experiencing sudden dieback in tree ferns. Given that the pathogen is so far unknown, there is no treatment, though it certainly wouldn't do any harm to feed the trees to see if that helps them resist whatever the problem is.
If your tree fern is exposed to any sun at all, specially the frond tips, that would explain what's happening - it's frazzling in strong sun. Otherwise, it's probably just the excessive heat.
The other cause of frazzled fronds is excessive wind.
This is good overall advice. Humidity can be an issue as well. Try watering frequently enough that the soil never dries out. You can't do too much against the wind, but depending on the height, you could cover it with a row cloth when the sun is brightest, to cut the amount that hits the leaves. The temperature will be slightly higher, but the relief from full sun will be beneficial.
Fertilizing is healthy, but too much causes excessive new growth, which will be more susceptible to burn. If you fertilize, carefully read the instructions provided with the product, and never add more than directed. If you can, using an organic fertilizer/soil amendment like compost will be very healthy.