Trees aren’t just beautiful, they’re vital.
Our urban canopy, especially our native trees, provide significant habitat to birds, insects and animals, and strengthen our city’s biodiversity. Trees’ leafy shade eases our energy consumption on hot days. Trees provide carbon sequestration and help to clear the air of pollutants from the wildfire smoke that sometimes wafts our way.
And as the California drought continues to wear on, trees are hurting. The evidence is in their green color - specifically, their increasing lack of it.
“If you’re noticing a tree’s getting a bit shaded in that green color, that’s an indication of a problem,” said Dr. John Shribbs, chair of the City of Petaluma's Tree Committee and active member of the Petaluma Wetlands Alliance and ReLeaf Petaluma. “It’s like when you look at a person and say, ‘You’re looking a little pasty today, are you okay?’”
Shribbs’ home, not surprisingly, is an eco-haven of arboreal care-taking, where he blends a practice of water conservation with some creative ways of utilizing rain and gray water in his landscaping. Through his advising role to the city council and his work with the wetlands alliance and Releaf, he promotes both the importance and care of our urban canopy. To help our local landscape make it through the drought, Shribbs recommends planting native species of trees because of the drought resistance and survivability, as well as their contribution to local biodiversity.
It’s all about the bugs, he pointed out.
“Basically, my goal is to grow insects and feed bees and birds,” he said. ”We need to grow insects that feed the birds that are basically a part of our whole ecology and landscape, by providing habitat as well as food within our native trees. Imported trees are ecological deserts and native trees are full of life.”
On his own property, Shribbs grows native trees and uses their leaves (rather than bark) as mulch, because the leaves hold water better. He lets the leaves fall and remain, with the added benefit of providing habitat for native bees.
“We’re losing our native bees,” he said. “Native bees pollinate hundreds of times better than honey bees and the fallen leaves are where native bees will live.”
It’s also important to notice the size of the leaves on our trees.
“Especially oak trees, the leaves will become much smaller and there’s a slight cupping that happens when they are trying to conserve water,” he said. “Trees will do what they can to conserve water and will start folding up a bit.”
There are other indications of the trees beginning to struggle, he said, such as branches noticeably dying off.
“If you look at pine trees and they’ve lost all their needles at the top, that’s a symptom that the trees are hurting,” he said.
Non-potable water is a highly useful resource during a drought, reminded Shribbs, who uses a rainwater catchment system. He’s currently using last season’s rain to water many of his plants.
“Instead of letting the water drain into the storm sewer system, let it flow through your landscape first before it goes out to the street,” he said. “You want to conserve water by using your own personal watershed.”
He also encourages using gray water from your home’s shower and sink to water trees. The needs to be free of non-biodegradable detergents, soaps and shampoos or other harmful chemicals. One tip is to drill five or six holes in a five gallon plastic bucket, sit it on the ground by your tree (near where the roots are) and pour the greywater into the bucket.
“That lets the water drain out, forming puddles, seeping down slowly and getting deeper than even drip systems will go,” Shribbs said.
Younger trees need between 10-20 gallons of water per week with mature trees needing less. You should water during the cooler hours of the day to limit evaporation, and use a long screwdriver to check the soil’s moisture by plunging it into the soil. The soil should be moist but not soggy, down to at least 18 inches deep.
This is especially important for street trees.
Shribbs explained that street trees, located in the areas between the street and the sidewalk, are basically like a potted plant. Their root systems are confined to that small rectangular area, so are much more susceptible to damage, to root disease and to drought.
Trees in our yards, used to getting a drink from the watering of the nearby lawn, are also going to be at risk during the drought.
“A drip system covering the root area, and then doing a deep soak with a bucket and gray water once a month, should be enough water for them,” Shribbs said.
A tree’s roots will go out two or three times wider than the canopy of the tree, so you’ll want to get your drip line circling out wider than the canopy to reach those roots. “Don’t water the trunk,” Shribbs said. “Watering right at the trunk encourages diseases to get into the trunk.”
Live oaks, for the record, don’t need as much water. They’re designed genetically to be drought-tolerant, and too much watering will cause them to get root diseases. Shribbs suggests giving them a deep watering once a month.
Finally, since trees also need nutrients, he suggests giving them an organic liquid fertilizer once a year in the spring, along with a deep watering to help the medicine get down deeper.
Shribbs care of trees comes from his belief that we are deeply connected to nature - including the living things that grow in our cities, alongside our sidewalk and in our back yards.
“We need to be a part of our local nature and try to enhance it and even have it right outside our doorstep,” he said. “That’s the new mantra, the new philosophy and we’ve got to move forward with that.”