Well, it sure feels like summer out there. The solstice has come and gone, and we are on the heel of a heatwave that has set records across the West. It’s pretty early to see temperatures this high for such a duration, so fingers crossed we get a good bit of relief here soon.
Shout out to our team! They have been doing a fantastic job of keeping up with the workload despite temperatures routinely topping 100 degrees. No doubt this heat is hard on outdoor laborers. Weather this hot is tough on trees, too. We rely on trees for so much, and this time of year we certainly don’t take them for granted.
Look around a parking lot. There will be cars parked in the very back even if there’s just a sliver of shade!
Know Your Trees’ Water Requirements
A native California buckeye, Aesculus californica in the South Yuba River Canyon. Always one season ahead, these trees are the first to leaf out in the spring, and begin to turn dormant in the summer, reducing its water requirements.
A good place to begin is by knowing the tree species on your property and their watering preferences. Native trees generally do not need irrigation. They are well adapted to the climate of this region and have deep root systems that allow them to make it through the hot and dry summer months. In fact, irrigation should generally be avoided around native trees. We have seen issues like root rot develop in natives that receive too much water, which can create a hazard. During the heat of summer, we sometimes recommend giving our native trees, more often conifers, some water on an infrequent basis. A good place to start is once or twice month if it’s been extremely hot and dry.
Generally, under the dripline of the tree you can expect there to be tree roots.
Trees prefer a deep watering for a few hours, in the evening or overnight, that covers the entire root zone. The root zone is typically within the dripline of the tree, see the illustration below. Adequate coverage is not easily achieved with drip irrigation, therefore we recommend some kind of sprinkler. Frequent shallow irrigation, such as a lawn would receive, encourages a shallow root system that leaves trees more susceptible to drought. It’s important to note, mature trees are more tolerant of low-moisture conditions than young trees.
Keep an Eye Out for Signs of Moisture Stress
Your trees will tell you when they are experiencing stress due to low moisture in the soil. In the early stages of low moisture conditions, leaves on a tree may look wilted, not unlike a houseplant. The edges of the leaves may then turn brown.
On the left is a Box elder, Acer negundo showing wilting and leaf scorch. On the right, Autumn blaze maple, Acer freemanii, showing brown spotting from drought stress.
Another sign of moisture stress may be little to no new growth on the tree. Typically, new seasonal growth will be lighter green in color and smaller. If you can't find any new growth on the tree, it could mean dry soil is the culprit. If dry conditions persist for a good while, portions of the upper crown will lose their leaves and die back. An example of this is shown in the common hackberry, Celtis occidentalis, pictured here in Grass Valley. These are tough trees which are extremely tolerant of poor soil, compaction, and drought. As far as I could tell, this tree was receiving no irrigation.
Make Mulch Your Magic!
Mulch is an easy way to give your tree a little extra help against the heat. Mulch increases moisture retention so less water is required to maintain the tree's health. It keeps the roots covered and cooler, and provides amazing nutrients. The decomposition process integrates a nice loam into the soil, aided by worms, critters, and fungi. I have personally found that mulched trees need at least 50% less water to maintain their health.
Raw woodchips from an arborist like us is considered the best mulch for trees. It’s not just chipped wood, it's also bark, twigs, and leaves that decompose at different rates to provide a rich organic material for your trees.
Bowie, takes a break from racing to rest on her throne of fresh wood chips.