I try to tell people that although we occasionally get torrential rain, this area is still dry. Even if this region hadn’t been in the midst of a drought for a decade, it’s still the Mojave Desert. We humans, as well as our pets, can go into the house and get something cool to drink, but plants, being rooted in the ground, just don’t have that option. Since almost all of our local landscapes came with irrigation already installed, it can be easy to forget that as trees and shrubs grow, their water needs grow as well.
How many of us could go out to our yards today and see trees that’ve been growing in place for five years or more? How many of us would see that they’re still receiving only the water provided by a couple of drip emitters close to their trunks? It’s highly probable - the tree needs a lot more water than it’s receiving, and obviously this can be a source of major problems.
I often talk to people about how essential good soil drainage is for plant health, which is definitely true. Although poor drainage is actually a major cause of landscape plant death, the opposite – a lack of water getting to roots – can also kill or injure them.
None of these symptoms is unique to a watering problem. A barren stem might be mistaken for an insect infestation. Examine that branch closely, and if there aren’t any critters on the leaves or under the bark, then think about water.
Patches of dead leaf tissue might be the result of an infection by bacteria or fungi, but that’s not too likely. We don’t have particularly big disease problems here in the Mojave since it’s so dry here.
A slow growing plant could need fertilization. Has it been given fertilizer in recent memory? If not, perhaps it’s time to fix that. On the other hand, it could simply be reacting to temperatures over 100°.
In the desert southwest, really, drought stress is more often the likely cause of plant discomfort than any of these, and it’s easier to remedy.
How does one check for watering problems? First, feel the soil. Is it dry? That’s a pretty good indication.
Take a look at the irrigation system. Are there enough emitters? One or two gallons per day will not support a mature tree in a well-drained soil, especially during the summer. Even a young tree may need a little more than that. A plant’s water need depends on the trunk diameter (that’s called the “caliper”) as well as the variety. A mature cottonwood, for instance, can easily transpire over 100 gallons daily. Usually the tree’s root system will extend through a wide area searching for water, but roots can’t grow in dry soil.
For landscapes in the summer desert, water shortage is an especially big issue. Take a look at your plants, and if they need more water, either add emitters, or start watering by hand.
For KNPR’s Desert Bloom, this is Dr. Angela O’Callaghan of the University of Nevada Cooperative Extension.