Tag: mesquite trees

4 desert trees good for the soil and 4 toxic ones

Recently Tucson’s Mayor Romero announced a tree planting goal for the City: one million new trees planted in the next ten years to help combat climate change. (That works out to 274 trees a day!) Homeowners are encouraged to plant one or more trees around their homes. But the number of tree choices for hot dry gardens runs into the dozens. So how to choose?

Trees related to peas?

In the hot dry gardens of the Mojave and Sonoran deserts homeowners should consider the benefits of planting these 4 trees that belong to the pea family. Why pea family trees? Because they take in abundant nitrogen (NH2) from the air and convert it to ammonium nitrogen (NH4) which gets added to the soil via bacteria-filled nodules on the tree roots.

So, not only do these trees do what all good trees do–provide shade and remove carbon dioxide from the air–they also help other plants beneath and nearby to thrive by providing nitrogen to the soil for nutrition.

You see this everywhere in untouched, natural areas, like this photo from the Saguaro National park: cacti and other plants growing right under and up through trees.

Food for the soil and plants nearby

First on the Good-for-the-Soil List: Mesquite (Prosopis). Among the most common varieties of Mesquite are Argentine mesquite (P. alba), Chilean mesquite (P. chilensis), honey mesquite (P. glandulosa), the screwbean mesquite (P. pubescens ) and velvet mesquite (P. velutina). The honey and velvet mesquites produce edible seeds pods that are commonly ground up into a flour for cooking. The screwbean is quite a messy tree. In size, mesquites range from 8 to 10 foot tall shrubs to 40 foot tall trees.

Mesquite tree prosopis
Mesquite alba in Las Vegas

They are super-easy to grow. On my short walk this morning I noticed dozens of young volunteer mesquite trees sprouting along neglected areas next to the street. If they are left alone, within a few years they will become trees with no help from anyone.

Trivia: in Australia and Ethiopia mesquites were introduced a few decades ago and loved the weather and land so much that they are now regarded as invasive pest trees because they are aggressively taking over grazing lands.

palo verde tree at Sunnyland garden
“Palo Verde Tree, Sunnylands, CA 2-22-14” by inkknife_2000 (11.5 million views) is licensed under CC BY-SA 2.0

Second on the Good-for-the-Soil list: Palo Verde trees (Parkinsonia florida), the Official Arizona State Tree. In Spanish the name means “green stick” with good reason. It is immediately recognizable by the green color of its trunk and nearly leafless branches. In Spring it bursts into bloom with brilliant yellow flowers and small leaves emerge, only to fade away quickly. While it does not cast much shade, it too helps other plants thrive by fixing nitrogen in the earth. The Foothill Palo Verde, which has a more yellow tinge to the trunk, reaches 20 feet in height. The blue Palo Verde can grow to 40 feet tall.

Acacia in bloom at Los Angeles Arboretum

Third, we have the Acacia tree (Acacia), which some claim should be knick-named the “Allergy Tree”. These fast growing Southwest natives love the heat and bloom with yellow powder-puff flowers in the spring that leave a pretty carpet of yellow pollen and spent blooms beneath them. Some also bloom again in the Fall. The larger varieties will reach 40 feet in heights and provide excellent shade, but there is one smaller variety suitable for courtyards.

Food for the soil and people, too
“Carob tree” by tree-species is licensed under CC BY 2.0

Fourth, and a little harder to find, is the Carob tree (Ceratonia siliqua). Not only does this Mediterranean native tree add nitrogen in the soil, it has pods that, when ripe, can be ground up and used as a substitute for chocolate. Be sure to read instructions online if you plan to do this.

Growing to a height of 50 feet carob trees cast dark, cooling shade. Unlike the previous three on this list, it needs some water year ’round. It is, however, on the suggested tree list in Tucson. For whatever it is worth, it is one of my favorite trees and Carob ice cream was very popular among the hipsters in San Francisco in the 1960s.

4 Toxic beauties

But not all trees in the pea family are good. There are some toxic trees in the pea family which are quite beautiful and are planted in hot dry gardens throughout the Southwest–and probably shouldn’t be. While they can fix nitrogen in the soil they are best NOT planted in a family garden because of the dangers they can pose.

The Golden Medallion tree
Golden Medallion tree in Tucson

The striking Golden Chain tree (Laburnum × watereri) is uncommon, temperamental, and all parts are poisonous. The brilliant yellow flowers hang down like long chains of gold, which is where the name comes from.

The Golden Medallion tree (Cassia leptophylla) is similar in appearance to the Golden Chain tree. Its pods are poisonous.

The umbrella-shaped Mimosa tree (Albizia julibrissin) with its pretty pink-white flowers has poisonous seed pods and a reputation for being invasive.

The small Texas Mountain Laurel (Dermatophyllum secundiflorum) is a shrub-like tree with lovely purple blooms that look like wisteria or lilacs. Its brilliant red seed pods are deadly poisonous.

For more information about trees suitable for hot dry gardens, go to our Leafy Trees for Shade page.

Our 8 most popular newsletters

  1. Where to get free or cheap trees for your garden
  2. Six distinctively different landscapes to replace a lawn
  3. Cover up that naked wall
  4. Five fragrant plants for your garden
  5. Nine trees to combat climate change
  6. Four desert trees good for soil, 4 toxic ones
  7. Plants that bloom even in mid-summer scorching heat
  8. Follow 90F degree rule for planting

Mesquites and flowering trees to plant in your hot, dry garden this Fall

Mesquites seem to have become the Street Tree of choice in some cities in the arid Southwest.  Cities can line the streets with allées of Honey mesquite (Prosopis glandulosa) or Velvet Mesquite (Prosopis velutina) knowing full well that maintenance is not going to break the city budget.  As natives these trees thrive in harsh, dry climates with almost zero upkeep. And Fall is the best time to plant them.

Mesquite prosopis
The Mesquite is for all practical purposes a plant-it-and-forget-it tree, but the shade it provides allows other plants thrive.

When you plant keep in mind that  irrigating and fertilizing a mesquite is a mistake and planting one in a lawn that is regularly watered can be a disaster: the roots will be shallow, the tree will become top-heavy and topple over in the Spring and Fall windstorms.

A third native mesquite, the Screwbean (Prosopis pubescens) is more of a tall, thorny shrub and is best planted in an out of the way place.  One Screwbean mesquite I saw not long ago was tucked back in a no-irrigation zone of a large Las Vegas garden where it and a nearby Desert Willow (Chilopsis linearis) were surrounded by a protective circle of agaves.  A good choice of companion plants!

Desert Willow and agaves
A Desert Willow and a Screwbean Mesquite make good companions to these agaves.

In addition to these three, other mesquites from Chile and Argentina have been introduced into the Southwest and have cross-bred like crazy with the locals. And thorns have turned up unexpectedly on supposedly thornless mesquites.

The problem with these fast growing, very drought tolerant trees is that they don’t give us colorful blooms in our gardens.  Yes, yes — I know they “bloom”–after all, that’s where Trader Joe’s Mesquite Honey comes from–but the blooms are very subtle.  Bees may notice them, but the average person driving along the street won’t.

So here are a few recommendations of trees to plant this fall that will produce colorful blooms in summer.

The first two I have already written about but are worth mentioning again.

chitalpa tree
This Chitalpa tree was planted as a “whip” about 4 years prior to this photograph being taken.

The  Chitalpa tree (Chitalpa x tashkentensis) was especially developed for low water usage gardens — by Russian scientists, no less.  The “tashkent” in its name is the capitol city of Uzbekistan formerly part of the old Soviet Union  where the scientists worked. Why those scientists spent time developing a ornamental garden tree–rather than a practical fruit or nut tree–I will never figure out.  But I thank them.

Anyway…it is definitely a favorite because it blooms in pink, or white, or lavender  for months on end in summer. It needs some watering, grows 2 or 3 feet a year and reaches a height of 25 feet tall. Bonus:  hummingbirds love it.

Crape myrtle
In addition to pink and hot pink, one Crepe Myrtle has showy white flowers in summer.

The Crepe Myrtle (Lagerstroemia indica) can be a glorious blast of color in the summer, although be aware that it does need watering to do its best. A row of them behind our local library did not get irrigated this summer and failed to put on the usual bright show of flowers.

By nature the Crepe Myrtle is a shrub although some plant growers train them to be a small tree or standard.  It tolerates neutral to slightly alkaline soil so be sure to add mulch around it at least once a year.

The Gold Medallion tree (Cassia leptophylla) is a Brazilian native that is now being planted in drought tolerant landscapes in the Southwest after being introduced to the U.S. by the Los Angeles Arboretum in 1958.

Brazilian gold medallion tree
This young Gold Medallion tree will easily grow to twice this height.

It flowers with huge basketball size clusters of yellow flowers at the ends of branches and the hotter the weather the more the blooms.

Happily, it also tolerates mildly cold weather down to 25° F for a short time. The City of San Francisco, of all places, is using it as a street tree and it is chilly there, for sure!  The Gold Medallion tree needs soil that drains well and do not over-irrigate. It’s seeds are poisonous.

Now about Oleander…Yes, it blooms in summer, is drought tolerant, and grows fast. And every bit of the plant is poisonous–leaves, branches, flowers–everything. Seriously, it can kill people.

CLIMATE CHANGE
In the last few days many of us in the Southwest were blessed with rain. It soaked into the earth in some places and in other areas created flash floods. This rainfall came from the remains of Hurricane Sergio.  As the Pacific ocean warms up along the California coast, we can expect more after-effects from hurricanes and, before long, full-fledged hurricanes actually blowing into Southern California and eastward. This year the water temperature off So. Cal. was 78° F. That’s 10° above the historic normal. The weather folks tell us hurricanes need 80° F water temperature for energy–and that’s only 2 degrees away.  I look at the photos of the destruction caused by Hurricane Michael in Florida and hope we do not have to experience that here.

Our 8 most popular newsletters

  1. Where to get free or cheap trees for your garden
  2. Six distinctively different landscapes to replace a lawn
  3. Cover up that naked wall
  4. Five fragrant plants for your garden
  5. Nine trees to combat climate change
  6. Four desert trees good for soil, 4 toxic ones
  7. Plants that bloom even in mid-summer scorching heat
  8. Follow 90F degree rule for planting