Today’s blog post title is a play on the old saying “you can’t have your cake and eat it too.” In other words, once you’ve eaten the cake, you don’t have it anymore. Likewise, if you have a tree, you’ll need to use a lot of water which might run afoul of water restrictions. Or will it? Today’s post demonstrates that you can have healthy trees AND save water at the same time.
A few weeks ago I got an email from ISA-certified arborist and blog reader Curtis Short, who wanted to share his success with rejuvenating a prized landscape tree that had become severely stressed as a result of residential water restrictions. The tree is camphor (Cinnamomum camphora), which grows well in warmer parts of the country (USDA hardiness zones 9b-11b). This particular tree is about 40 years old and the showpiece of a residential landscape in the Oakmont neighborhood of Santa Rosa, CA.
In March 2022 Curtis received an email from the homeowner (a retired meteorologist) who was concerned about the declining health of the camphor after irrigation was discontinued in mid-2021. Prior to this, the sprinklers were run daily during the dry months to support the tree as well as the surrounding lawn. The lawn, with its shallow but dense root system, recovers quickly with seasonal rains. The damage to the tree’s root system, however, has led to leaf senescence and drop.
Two other arborists had given the tree a thumbs down: one said it needed to be removed and the other said that even if the tree recovered it would never regain its original form. Curtis chose a different approach, suggesting that the homeowner could resuscitate the tree by:
*removing competition (the lawn) for water and nutrients,
*refining the irrigation system,
*applying nitrogen to stimulate new leaf growth, and
*supplying an arborist chip mulch to the landscape.
In April the homeowner applied glyphosate to kill the lawn, removed the old lawn sprinkler system, and replaced it with a 100-foot drip irrigation system near the canopy dripline and outwards where most of the tree’s fine roots are located. (For those who are curious, the system consisted of 12-inch spaced Techline emitters with a 0.9 gallon per hour dispersal rate.) Next, a layer of arborist wood chips were applied to at least a 4” depth. In May, ten pounds of ammonium sulfate (a great source of nitrogen) were applied on top of the chips and watered in.
The homeowner’s irrigation plan departed dramatically from the original daily watering routine. Being a retired meteorologist, the homeowner was naturally interested in collecting data. The original two lawn stations each put out 45 gallons per day, for a total lawn water usage of 630 gallons per week. With the new drip irrigation system, irrigation was limited to one 35 minute application per week, with a total weekly water use of 105 gallons.
Curtis photographed the tree’s recovery as a way to reassure the homeowners that the tree was neither dead nor disfigured. The homeowners are now aware that trees cannot go “cold turkey” in efforts to reduce irrigation water use. Locating the drip system beneath the mulch layer means evaporation is reduced and that the mulch layer stays hydrated, supporting its population of mycorrhizae and other beneficial microbes.
I appreciated Curtis sending me this case study as we all face the likelihood of hotter temperatures and possible water restrictions. Reduction of water-hungry ground covers, judicious use of water, and a living layer of arborist wood chips are key to helping our landscapes survive.