6 Common Problems with Landscape Trees in the Sonoran Desert

In this article I would like to cover the six most common problems we run into with landscape trees here in the Sonoran Desert. Some of these problems are easily fixed but others will be with the tree all its life.

 1)      Wrong Tree in Wrong Place

When you choose a tree, you need to consider its mature size and shape. While a small “Christmas Tree” may look cute right next to the house, a 60ft Aleppo Pine towering over a home can be a hazard! Eucalyptus trees are another common offender.

The power companies need to maintain at least 10ft of clearance between their lines and any trees. If you are planting under wires you need to take this into consideration!

Pine Tree Under Powerline?

You can also end up with a tree that dominates the landscape because of its scale in a small lot. There are many small “patio” trees which mature at a short height and work well in tight situations or under power lines.

2)      Poor Nursery Stock

When you pick a tree from the nursery, you will usually pick one that looks full and healthy, right? What else would you look for? Well, what is below ground is actually more important than what is above ground! When a nursery allows circling roots to form inside the rearing container, there is really no hope for the trees long-term survival. These circling roots will not straighten out; they will only grow in girth and eventually strangle the tree!

Check out the girdling roots on this Bookleaf Mallee! (It had died...)

Without X-Ray vision (wouldn’t that be handy?!) it is impossible to know what is inside the soil in the plant container. You need to deal with a nursery that follows best management practices for nursery stock! Each time the plant is “bumped” into a larger container the roots need to be pruned. If the nursery doesn’t know what you are talking about when you ask about this, GO SOMEWHERE ELSE!

When you plant the tree you also need to prune the roots on the outside of the root ball. With a 24” box tree we typically cut off 1-1/2” from the outside. This takes care of any recent circling roots.

 3)      Planting Too Deep

Trees need to be planted so that the trunk is in the air and the roots are in the ground. That is the way they are made! Rocket science? Not really, but then why do we see so many trees planted 6-12” too deep? You need to carefully look at the tree to find the place where the trunk ends and the roots start. This may not be at the soil level in the container from the nursery! It is usually indicated by a swelling in the trunk.

When we see a tree go straight into the ground with no flare to the trunk, we know it is planted too deep. Excavating around the trunk to expose it to the air may help the situation if the tree has not been in this condition too long. Long-term, having the trunk in the ground is a stressor and can cause premature death.

A 4ft Mesquite planted at least 10" too deep!

4)      Improper Staking

Does the tree have stakes on it? TAKE THEM OFF! “Guys” can be used according to the ANSI standards, but only for specific objectives. Staking new trees should rarely be done, and for six months to one year maximum! If the tree has not established itself in this period of time, there are likely problems related to points #2 and #5. Nearly 100% of the trees that we clean up after storms have one or both of these two problems.

Poor little Mesquite tree staked tight! The wooden stake has already rubbed completely through the bark in several places!

We have spent a fair amount of time over the years trying to stand up and stake trees that tip over in storms. Usually after two to three attempts, we end up taking the tree out and find that it had problem #2. I now feel that when any tree (other than a very new one – in the ground for a few months) tips over, it is best to take it out and start over with good nursery stock.

A Palo Verde tree - staked forever...

Closeup of the above tree - do you think this is healthy for the tree?

 5)      Improper Watering

Water for trees needs to penetrate the soil to a depth of about 18”. The soil needs to dry out fairly well between waterings. The frequency and duration of watering will depend on your soil type, but the plants themselves can be an indicator!

Most of the trees here in the Sonoran Desert are both cold and drought deciduous. That is, they lose their leaves when they get too cold or too dry as a survival tactic. If you see the leaves starting to die and fall off your Mesquite in the summer, it is probably too dry. Give it a good drink! The majority of a trees roots are within the top one foot of soil directly under the canopy of the tree. There will, however, be roots extending out two to three canopy diameters from the tree! When you water, you want to cover the majority of the roots – under the entire canopy, not just at the trunk of the tree! Watering at the trunk makes that soil soft – right where the main anchoring roots are! You don’t want your tree to be trying to stand up in mud! Distribute the water out away from the trunk and your tree will be happier and less likely to tip over in a monsoon storm!

You probably WON’T see the leaves dying and falling off your ESTABLISHED Mesquite tree in the summer because your ESTABLISHED Mesquite tree probably has its roots into all the landscape plants in your yard! SO, your Mesquite tree PROBABLY DOESN’T NEED ANY IRRIGATION! Same with most of our desert trees. You can judge how much water the tree is getting by looking at how much it grows each year. If your Mesquite is growing more than a couple feet each year it is getting more water than it needs! Most are!

A new tree especially needs to have the drip system emitters spread over a fairly large area to encourage root growth and establishment. We like to put six emitters on a new 24” box tree, distributed out from 3 to 6 feet from the trunk. One of the six can be on the root ball for 30 days and then moved out. A new 24” box Mesquite tree should grow roots out 10-12 feet in all directions in 30 days in the summer, 90 days in the winter – if there is water available! How could such a tree tip over? Why would it need to be staked?

 6)      Improper Trimming

There are a couple basic principles that we follow in pruning a tree. First, branches need to be cut back to a fork. Second, there should be a reason to make each cut – an objective. Usually with desert trees the objectives are to raise the canopy so there is clearance under them to walk or drive, and to thin the canopy so air can move through it more freely. Another objective might be to get the branches off the roof or away from the walls of a house. When done right this can look very good!

Topping a tree (which is cutting the branches off at a predetermined height irrespective of any forks) is against ANSI standards, is ugly, is costly, and ruins the structural integrity of the tree for life! DON’T DO IT!

If a tree is “too tall” then it may be possible to make reduction cuts and lower the canopy to a certain extent. Another good choice would be to take out the tree and plant something more appropriate (problem #1).

When we start to work on a tree that we have not previously trimmed, we start by cleaning off all the stub cuts (cuts not made to a fork) that landscapers have done in the past. Then we take out deadwood. Next we make those cuts we need to make to meet our pruning objectives. Finally we work on crossing branches and branches that don’t fit in.

Stub cuts in a Mesquite tree.

While we are working, we try to estimate the percentage of the canopy that we have removed. The rule of thumb is to remove less than 20-25% of the trees canopy in any one calendar year. Younger trees can withstand percentages in the higher end of the range. If we can’t correct all the problems in the tree without going over our percentage, we do what we can this year and plan to make the rest of the corrections next year.

Usually when improper pruning has been done to a tree we have less options available when deciding which branches to remove. It is possible that because of the way the tree has been treated in the past, there may be no good options and you’ll either end up with an ugly tree or need to take it out and start over.