Drought! Drought! Drought! This is all we hear at seminars and read in every tree industry magazine that passes through our office. A lot of the trees we manage are showing signs of drought stress. Twig elongation is shorter than last year, leaf density is lower and so is overall tree health and vigor. We are removing many trees that have simply given up and died.
Most trees live close to their limit of survivability even under ideal conditions. When more resources become available, trees tend to grow faster. If there is some kind of limiting factor, trees tend to grow more slowly. A dramatic decrease in water is probably the strongest limiting factor out there.
A new option for thirsty trees
The extreme conditions produced by the current drought have 
caused us to offer a new tree watering
service.Depending on the size of the tree in question, we have been applying between 100 and 500 gallons of water to the root zone. We add an organic wetting-agent to the water to help it penetrate the soil, as well as a diluted (and secret) bio-stimulant to help soil health. A lot of the organisms typically found in soil are dying from lack of soil moisture. This bio-stimulant helps keep the beneficial soil organisms alive and healthy. This watering does not affect the customer’s water bill; although as you can imagine, it does affect ours.
Some tree purists might argue that this process seems over the top and possibly unnecessary, and they have a point. If I were a tree owner and I was given the choice of watering my own tree, paying someone else to water it, or watching it die I’m pretty sure I would have a soaker hose out doing some nice slow watering for at least six hours every two weeks. However, if that wasn’t something I could do and my choices were to either pay for the removal of the dead tree or have a watering service keep it alive, I would opt for the latter.
Trees need a lot of water!
Small new trees have a small root zone, so they can only pull water from a small volume of soil. Large trees have a much larger root zone and a corresponding larger volume of soil to pull water from, but they also have greater water needs. When we say that large trees are well established, it means that they are structurally established in the local environment, it doesn’t mean that they no longer need supplemental water. Some trees, like the Mesquite and California Pepper, are drought-tolerant, meaning they are stingy in their water use. They still need water, just less than a tree that would typically be found at the bottom of a canyon near a creek, like an Alder or Sycamore. River-side tree species that are commonly used in the urban landscape need a lot of water and can die when they start getting less than normal, or when the weather heats up and their programmed irrigation doesn’t match their species needs.
In response to the drought, many municipalities are rewarding people for turf removal. San Diego offers $1.50 per square foot to replace grass with water-efficient landscape. That sounds great. I’m not a huge fan of turf anyway since it gets in the way of trees’ roots. But if you make the decision to pull out a large section of your turf and turn off those costly daily sprinklers, spend some time considering where your trees are going to get their water. The city of Las Vegas went through this at least ten years ago. They paid people to replace turf and then tree removal companies made a killing taking out trees that had died soon after the turf and sprinklers were gone.
When thinking about the urban landscape, it is important to prioritize the different (and sometimes competing) elements found there. If you want to keep your trees, make plans to ensure they get the water they need to survive, whether that means instructing your landscape provider to arrange irrigation for them or contracting with a watering service. Whatever you decide, please remember to water your trees!
~ Peter Green, Plant Health Care Manager