If you’ve just landed in Scottsdale and asked someone about the tree with the green bark, the answer is palo verde, and you’ll see a few hundred of them before you reach your hotel. It’s the state tree, the most common tree in the natural desert and in the medians alike, and the reason the whole city goes yellow for a few weeks every spring. It’s also three or four different trees that people call by one name, which is where this guide comes in.
Our desert plants field guide introduces it alongside the saguaro and the ironwood; the palo verde lexicon entry has the short version and the pronunciation. This is the long one.
What “palo verde” means
Palo verde is Spanish for “green stick,” or green pole, and the name is exactly descriptive: the trunk and branches are green because they photosynthesize. According to the Arizona Native Plant Society, about three quarters of the tree’s food is made in its bark, with the tiny leaves doing the rest. That’s the trick that lets a palo verde drop its leaves in a drought and keep working, and it’s why the tree looks leafless and alive for most of the year.
Locals say it two ways, PAH-lo VAIR-day with a Spanish ear and palo VER-dee with an Arizona one, and nobody will correct you for either. The word is also on a lot of other things around here: streets, schools, a nuclear plant west of Phoenix, and Palo Verde, the dining room at the Boulders. Context usually sorts it out.
The state tree, and the question the legislature didn’t answer
The Arizona legislature named the palo verde the state tree in 1954. It did not say which palo verde. Arizona has two native species, the blue and the foothill, and the Native Plant Society’s reading is that both share the title. So if anyone asks which one is the state tree, the right answer is “yes.”
How to tell them apart
There are three you’ll meet in Scottsdale, two wild and one bred for yards.
Blue palo verde (Parkinsonia florida, still sold as Cercidium floridum on some nursery tags):
- Bark: blue-green when young, aging to gray on old trunks.
- Flowers: bright, deep yellow, five petals all yellow, with small red-orange spots at the base of the top (banner) petal.
- Leaves and thorns: bluish-green compound leaves with very small leaflets, and pairs of straight half-inch thorns where the leaves meet the stem.
- Shape: a big, drooping, rounded crown, 20 to 40 feet tall, often with several trunks from near the ground.
- Where: along washes, plains and canyons, wherever there’s a little extra water, and in almost every irrigated median in town.
- Life: fast-growing and relatively short-lived, about 30 to 50 years in the wild.
Foothill palo verde (Parkinsonia microphylla, also called yellow or littleleaf palo verde):
- Bark: yellow-green.
- Flowers: paler yellow, smaller, four yellow petals and one white or cream banner petal. This is the easiest field mark.
- Leaves and thorns: four to eight pairs of tiny leaflets, so small the tree looks bare even in leaf, and branches that end in thorny tips.
- Shape: stiff, upright and twiggy, usually well under 30 feet.
- Where: the rocky slopes and bajadas of the desert uplands, which in Scottsdale means the McDowells and the Preserve.
- Life: slow and very long: the Native Plant Society says more than 200 years.
‘Desert Museum’ palo verde (Parkinsonia × ‘Desert Museum’):
- What it is: a complex hybrid, Mexican palo verde crossed with foothill, and the offspring crossed with blue, selected from seedlings grown by Mark Dimmitt at the Arizona-Sonora Desert Museum in Tucson.
- The giveaways: no thorns at all, an upright habit, and big flowers over a very long season, two months or more.
- Shape: about 30 feet high and wide, and fast, up to eight feet a year when young.
- Where: resort courtyards, new subdivisions, HOA common areas, and the front yard of roughly every house built in the last twenty years. If it’s in a planter and it doesn’t have thorns, it’s probably this one.
A quick field test: look at the flower and the thorns. All-yellow flowers with a spotted petal and thorns at the leaf joints: blue. A white petal and twiggy thorn-tipped branches on a hillside: foothill. No thorns, a planter, and flowers that seem to go on forever: Desert Museum.
Bloom dates
- Blue palo verde: March into April, peaking in April in the Valley. This is the yellow you see along Scottsdale Road and in the medians first.
- Foothill palo verde: April into May, a couple of weeks after the blues, on the mountain slopes. It depends on moisture and can skip a dry year.
- Desert Museum: in the same spring window, but stretched out over two months or more.
A wet winter means a heavier bloom, the same rule that governs the wildflowers. The April page has the timing for the year, and May the tail end, when the foothill bloom on the McDowell slopes overlaps with the ironwoods going purple.
Why every yard has one
Three reasons, all practical. A palo verde is native and drought-tolerant: the University of Arizona’s extension notes for the blue palo verde say it needs no water once established, though extra irrigation makes it bigger and denser. It’s fast, so a builder can plant one in a new yard and have shade before the escrow papers are framed. And the Desert Museum hybrid gave landscapers a thornless version that’s safe beside a patio. Add the light, dappled shade that lets plants grow underneath, and you have the default tree of the xeriscape era.
It’s also the desert’s great nurse tree. Most wild saguaros start life in the shade of a palo verde or another legume, dropped there by a bird, and plenty of old saguaros are still standing next to the tree that raised them.
Yard care
Water deep and rarely. Once established, a palo verde on rainfall alone does fine in the desert. In a yard, an occasional deep soak beats a daily shallow drip, because deep water grows deep roots, and shallow-rooted, over-watered trees grow too fast and fall over in the monsoon.
Prune lightly, and never top it. The Desert Museum’s care sheet says its hybrid needs only minimal pruning, mainly watching for two competing leaders and cutting one so the other dominates. For blue palo verdes, extension guidance is to thin the crown while the tree is young to build strong branches, and not to strip off too many lower limbs at once: big pruning wounds invite bacterial wetwood and a mess of weak shoots. Topping a palo verde, the cheap-crew special, produces exactly that weak growth, and it’s what splits in July winds. The monsoon is when you find out who pruned your tree.
Watch for mistletoe. Desert mistletoe, the clumps of leafless stems that birds spread from tree to tree, is a real problem on blue and foothill palo verdes. Cut it out promptly.
Plant it away from the pool. A mature palo verde drops a carpet of flowers in spring and seed pods after, and both float. The pool season entry and our first-year notes say the same thing: over gravel, not over water.
Mind the cold, a little. The Desert Museum hybrid is about as hardy as its parents: young trees have frozen to the ground in the low teens, while trees with a few inches of trunk have come through 15°F undamaged. A Scottsdale winter freeze rarely gets there, but the north end of town and the foothills run colder.
The palo verde beetle
Every monsoon, someone in Scottsdale posts a photo of a beetle the size of a small mouse on the back patio. That’s the palo verde root borer (Derobrachus hovorei, called D. geminatus in older books), one of the biggest beetles in the region; adults run about three and a half inches.
The life cycle is the interesting part. The grubs live underground for up to three years, feeding on roots, and the adults come out during the monsoon, fly in the evening, don’t eat, and live only a few weeks, just long enough to mate. They look terrifying; the University of Arizona calls them gentle giants. Scoop it into a box and put it in the yard.
Are they killing your tree? Probably not. University of Arizona entomologists note that the borers are often wrongly blamed for dead palo verdes, when stress and environmental factors are the more likely cause. They do go after weakened trees, and there’s no effective chemical treatment; the defense is a healthy tree, which means the watering and pruning above. If the tree is dying, look at how it’s been watered and cut before you look at the beetle.
Where to see them
- The Xeriscape Garden at Chaparral Park, free and labeled, the best place to compare species side by side before you plant one.
- The Desert Botanical Garden in Papago Park, for the full family, in bloom in April.
- Brown’s Ranch and the Preserve trails, for wild foothill palo verdes standing over young saguaros.
- Any wash in town, for the blues.
The palo verde has neighbors worth knowing too: the ironwood, gray and evergreen, and the mesquite, with the dark bark and the real shade. Learn those three and the desert stops looking brown.