Evaluating the cold damage on your palm trees

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Although mostly people talk about how hot it gets in Phoenix (and it does!), it can get very cold. It did a couple of weeks ago, getting down below freezing for several nights in a row. The ability of a plant to stand cold is its "hardiness", which is as important here in Phoenix as its ability to stand the heat. These extremes of temperature are what makes it more challenging to grow tropicals here than in Hawaii, or Southern California.

To evaluate the damage on your palm trees, first you have to know what kind of palm trees you have on your property. If you have Washingtonia robusta (Mexican Fan Palms), you have no concern. And, as a general rule, if your palm trees are essentially "telephone poles", the cold won't hurt them. The miniatures are the ones you need to be concerned about, specifically those beautiful dwarf date palms, Phoenix robellini.

 Phoenix robellini only grow, at the most, to about twelve feet tall. I planted my oldest ones when I bought this house, twenty years ago, and they are now about my height, six feet. At that size, they are resistant to cold, but they will show damage. Smaller than that, the type of cold that we got here a couple of weeks ago can kill them. But there are things that you can do to help.

• Do nothing. If you go out there and start cutting away the damaged fronds, you will expose the tender new growth to more cold, and the tree has a better chance of dying. Leave it alone. Yes, the outer fronds will have to be trimmed off, and they will become browner and more unsightly for the next couple of weeks, but they will also be protecting the heart of the plant, where the new growth begins.

• Don't water. Your watering system should have been turned off in December. If it's still on, it will just encourage more tender growth, which will die. And tropical plants don't like getting a cold shower any more than you or I do. If it rains, which I'm hoping it will do, the humidity in the air will rise and there will be cloud cover, which will temper the shower. Nature knows what to do.

When the weather warms up again, trim the fronds back to the reveal the green center new growth. If there isn't any, the plant is dead. There is nothing you can do, the cold killed it. If you're wondering if it's really dead, gently tug the center with finger pressure. If it pops out, the plant is a goner. Dig it up and plants something else.

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