Until just a few years ago, Southern California's iconic palm trees were treated as though they were indestructible. The prevailing practice was to cut off as many leaves as possible so as to avoid having to come back and prune them again for as long as possible. This left the palms with just a few leaves, looking like a pointy paint brush. But then, tree care professionals, known as ISA Certified Arborists®, noted that this severe pruning was causing permanent damage to the palms. So representatives from 14 tree-related organizations, including the International Society of Arboriculture, USDA Forest Service, National Park Service, and the
Tree Care Industry Association updated the American National Standards Institute Pruning Standard, known as ANSI A300. The palm pruning standard is pretty simple, and following it will help you have beautiful and healthy trees. The first section recognizes that stuff falls off from palms that can hurt people and their stuff if it hits them. Another reason is that the dead leaves are a fire hazard. Recent wildfires have been spread by blowing burning palm leaves.
Some cities require palms to be cleaned regularly. Section two says that you shouldn't remove healthy, green leaves (fronds). Section three says that you shall not remove fronds above a horizontal plane that is the same height as the bud of the palm tree. That would leave, at least, a hemi-spherical canopy of leaves on the tree. Removing more leaves than that is no longer an acceptable practice. Sections 4 and 5 say that you should cut the leaves close to the trunk, and if you are going to peel the old leaf bases off, you have to do it without damaging the trunk.
So why do palms need all of their leaves? Well, the leaves are the energy-capturing part of the tree's economy. The trunk and roots are the energy users, and they also act like an energy-storage bank. When you cut a lot of green leaves off a palm, the energy income goes way down. If you cut half the green leaves off, that's a 50% cut in income. But the trunk and roots are still burning the cash at the same rate. So you can see how a palm with a big fat trunk could deplete its resources quickly. When that happens, it can't grow its trunk as well or defend itself against insects and diseases either. A weakened palm will develop a permanent narrow spot in the trunk which could be where it breaks off years later.
Now, there are exceptions. You can cut off fronds that are scraping your roof or hanging down in a path or drive, or if they are too close to utility wires, call your electric company. Stay away from power lines! You should remove flower buds, flowers, and fruit (seed stalks), since these can be messy and hard to walk on.
Remember that if you don't have to prune your palm, the skirt of leaves is habitat for birds ranging from kestrels to orioles, and insect-eating bats.