Especially when trees are newly planted, they need all the help they can get.
When cities and communities commit to planting trees, they don't always take into account the aftercare that is needed to ensure the trees' survival. New trees need a lot of water, and they often do not get enough from rainfall. Scorching summer temperatures only worsen the situation.
This is where residents can get involved – by helping to water newly planted trees, as well as those already-established ones that might be struggling in the heat. Arborists in London are calling on city residents to pitch in, using grey water to help the trees that shade their own streets. From an article in the Guardian:
"New street trees need at least 20 litres of water a week – about two large watering cans – from April to September, especially in hot weather. Any tap or grey water, including dishwater, bathwater and water from washing cars, windows and even clothes, is fine, as long as it does not contain bleach."
As the article explains, urban tree species are chosen for their resilience in a stressful environment, but it takes years for new trees to establish root systems that "can find their own sources of moisture among the networks of cables and pipes, and compacted soil under pavements and roads." In the meantime, a bit of help can go a long way.
Intrigued by the thought of urban residents rallying to help their new trees, I dug around some city websites to come up with a list of suggestions for how to do so effectively. Way back in 1982, the New York Times advised residents to run a hose for 15 minutes twice a week and to ensure it soaks in by loosening the top 2-3 inches of soil with a trowel every few weeks. The city of Santa Monica recommends removing turf (grass) from around the base of a tree, as it competes for moisture, and replacing with mulch.
There are numerous mentions of longer, less frequent watering being preferable to short, frequent watering, as it allows water to penetrate as much as two feet. This can be done by pricking holes in the bottom of a large trash can and filling with 15-20 gallons of water. Leave it at the base of a tree and allow the water to trickle in. Alternatively, place a coffee can near a tree and run a sprinkler; once the can has 2 inches of water in it, turn off the sprinkler. Davey Tree recommends watering newly planted trees every 2-3 days.
Using grey water is optimal, of course, as it recycles water. The NYC Department of Parks & Recreation writes on its website: "Ask building maintenance staff to water trees while they are hosing off sidewalks. Ask street vendors and merchants to dump water from their containers (coolers with melted ice or flower buckets) into nearby tree pits at the end of the day."
When everyone pitches in, the survival rate of these newly planted trees improves greatly; and it's a small price to pay for the majestic presence and welcome shade that they will someday provide.