How to water desert trees

Plants

Desert trees anchor a xeriscape. Such important plants need proper care to look natural and avoid damage. Amazingly one of the best things you can do for a desert tree is NOT water it all the time. Over watering encourages fast, weak growth. When summer windstorms come, a spindly tree loses main branches, potentially ruining its form. My neighbor had an entire tree disappear in a windstorm!

Severely_pruned_mesquite

This Mesquite is nearly full grown, yet has been severely pruned to prevent damage from wind. Watering less frequently would give a better natural form without the need for pruning.

When I plant a young desert tree, I build a basin with edges about 2 feet away from the tree’s trunk. I’ll start by watering the tree every few days for the first week or two while it recovers from transplant shock, then I fill the basin once a week while the tree gets established, about the first year. After a year, a desert tree can live with watering once every 2 to 4 weeks. If the tree seems to be growing slowly, you can increase the water frequency to no more than once per week.

Baby Palo Verde basin

A lush baby Palo Verde tree with a 2 foot basin.

As the tree grows, expand its basin. Once a year in spring you can rebuild the sides of the basin farther away from the trunk. The basin around the tree allows you to give a large drink with each watering, penetrating farther into the soil and allowing the trees roots to grow deeper. Shallow watering encourages shallow roots, which allows the top of the tree to become heavier than the root strength. In order to allow the basin to fully fill, turn a hose on at a trickle and set a timer for an hour, monitoring to make sure your basin doesn’t overflow. Or if your tree is on your irrigation system, you can add the number and flow rate of emitters needed to fill the basin in the time scheduled for your system.

Desert_tree_basin

A larger basin on a more mature desert tree. This basin measures about six feet across and is doughnut-shaped to encourage roots to spread away from the trunk. This tree blew over a few times while young and needed stronger roots.

Once my desert trees have doubled in size or seem well established, they can be watered even less frequently. A few of my trees border a low spot in my yard where water pools when it rains. These trees are not on my irrigation system and I hardly ever water them by hand. The winter and summer rains give them deep drinks which keep them healthy. They usually keep their leaves all season long, so I know they are getting enough water.

Juvenile_Palo_verde

This Foothills Palo Verde has been in the ground about 5 years and no longer needs any irrigation since it borders a low spot in the yard.

When watered appropriately, desert trees grow slower with more proportional shape and stronger branches. Over time they can still grow to mature heights of up to 30 feet, and much more quickly than they would in the desert.

Ironwood leaves die in spring?

Plants

This spring, all four of my young ironwood trees lost their leaves. The leaves turned yellow just as spring growth happened all around them. I thought somehow my trees were dying, though I didn’t see any reason why. About a month after the leaves started dying, I saw new growth. All four trees have now grown new foliage.

While I’m not sure why this happened, I’m glad the trees are still healthy. I found this information at desertmuseum.org:
“Branches that produce flowers often drop their leaves during bud formation, and re-leaf when summer rains begin”

My young trees have never flowered, but perhaps their leaves had remained on the tree long enough to need to be replaced. Ironwoods remain my favorite desert tree due to their size, leaf color, wildlife habitat, and shade. Some day I hope to have a large wildflower area with three mature ironwood trees as the backbone. I’m glad these trees are okay. They grow slowly and would be hard to replace.

Summertime landscape chores

Seasons

How did you enjoy the flooding?

basin flood

Phoenix flooding

With all of the rain, my landscape is looking green this summer! I’m especially happy that the young cacti in my yard that were a little sunburned look much healthier. The first year in the ground is always hardest for a plant.

My bushes grow more than average with the extra water, which means they look due for pruning. Since I don’t like gumdrop shapes, what is the best way and timing for pruning?

summer desert bushes

Bushes have grown and greened up with the rain.

I found a pruning schedule with recommendations specific to each plant. For many bushes it recommends only pruning once or twice a year. Here is another pruning overview by U of A. I’m surprised to find that they don’t recommend pruning Texas Sage in summer, since it tends to be one of the most often-pruned plants.

Texas sage

Texas sage in bloom, getting large and shaggy

A late summer pruning helps trim back excessive growth, but will reduce blossoming ends and could be put off until spring. If you prune, try selective thinning, where you remove entire branch sections, either to a fork or to the ground, to open up the bush. It’s harder, scratchier work, but results in a more natural shape.

Some desert trees should be pruned later in the summer (as opposed to spring) to prevent excessive growth. Now is a good time to thin Mesquites, Ironwoods, and Palo Verdes.

So, with that information, there’s probably less pruning to do than you thought. Perhaps just some thinning of a few plants that have grown more than you wanted during our rainy season.

Ironwood Trees

Plants

Ironwood trees are one of my favorite landscape trees for Arizona. You have probably seen them before, but because they are not brightly colored, you may not have noticed them. Here are some photos to help you identify the next one you see. The wood from ironwood trees is so dense it sinks in water. You have probably seen little statues carved from ironwood.

Ironwood_carving

Ironwood_youngandfull

This tree has been in my yard for a few years and gets watered twice a month. It’s canopy is green and full, and I have pruned it to have a singe trunk for the first three feet, then split into three main branches. I may raise the canopy in time, but it has plenty of space to grow wide, so I may just let it be. The thorns make pruning difficult.

Ironwood_form

This ironwood in a parking lot in Tucson has a nice form. I like the many trunks and branches with raised canopy.

Ironwood_large

This large tree is probably 25 feet tall. Remember the full size of the tree (30×30) when you plant so that you don’t have to take it out or fight (prune) with it yearly when it reaches mature size.

Ironwood_bush

This tree receives almost daily water and grew into a bush before its canopy was raised. Ironwoods can grow fast if watered frequently, but the form may not be as natural as a slower-growing tree.

Ironwood_native

Here is a native ironwood growing in the desert. The gray-green bark and airy foliage make it less noticeable, but it is a plant worth seeing. Ironwoods provide food and shelter for desert animals and birds. One site estimates that ironwoods are used by 150 bird species. The shade provided by an ironwood tree allows other plants to get a foothold in the desert. Any desert tree that shelters new plants is called a nurse tree.

Ironwood_220yearsold

This ironwood growing at the Arizona-Sonora Desert Museum is estimated to be 220 years old.

Ironwood_blossom

Ironwoods bloom in May with dusty mauve flowers. The tree blooms heavily in alternating years. None of the ironwood trees on my property have bloomed yet, making me wonder at what age or size the tree begins reproducing.

Woolly butterfly bush

Toughest drought-tolerant plants for your desert garden

Plant selection, Plants

In order to maximize the number of plants in your garden without overloading your drip system, you may end up planting things that you expect to survive on their own. Luckily, there are some un-prissy plants that can do this. These survivors deserve a medal, instead of being overlooked and under-appreciated. After all, this is the desert! When I moved to Arizona, the house I bought had been vacant for two years and some of the plants in the yard were still alive. That is the kind of landscaping I want.

Trees

Natives: Foothills palo verde, Ironwood, Joshua tree

Non-natives: Catclaw acacia, Whitethorn acacia, Elephant tree (frost sensitive), Smoke tree.

Shrubs

Creosote bush, Desert holly, Four wing saltbush, Jojoba, Las Vegas buckwheat, Limber bush, Mormon tea, Pink fairy duster, Shadscale saltbush, Warnock condalia, White bursage, Yerba santa

Woolly butterfly bush

Woolly butterfly bush

Wildflowers, agaves, yuccas, others

Bahia, Desert sunflower, Prickly poppy, Variegated century plant, Bear grass, Banana yucca, Our Lord’s candle yucca, Candelilla, Slipper plant, Bush muhly grass, Medicinal aloe