Give trees extra water, TLC during summer heat

Something to think about while taking a break in the shade: Our trees are a lot better off this summer than they were last year.

Summer of 2022 capped three years of epic drought. Summer of 2023 follows one of Sacramento’s wettest winters on record.

So heading into this very hot July, our trees had some reserves they didn’t have last summer. Heavy winter rain gave them a deep, lasting soaking. A cooler-than-average spring helped them grow.

“Most trees are doing a lot better – they’re showing a lot of growth and look very healthy,” says Alex Binck, community arborist for the Sacramento Tree Foundation. “Especially trees that have been in decline for the last several years such as redwoods; those trees are flush with new growth and just look a lot more green.”

The task this summer is helping those trees maintain their recent health gains. Sacramento’s notorious heat can bake away soil moisture quickly.

“We had a phenomenal year with a lot of rainfall and soil moisture,” Binck notes, “but we had years of moisture deficit. We’ll be back into dry conditions by late summer. There definitely will be soil stress by the end of summer.”

Trees – especially younger or newly transplanted trees – are at their most vulnerable when weather changes from cool to hot rapidly – which we have seen this past month. “Especially that first big heat wave after nice, cool weather,” Binck says. “Look at temperatures and increase irrigation if temperatures are going to spike.

“Trees seem to adapt to temperature changes over time, but that first heat can be challenging,” he adds. “With climate change, we expect to see more dramatic swings. For trees, dramatic swings can be more stressful.”

During July and August, young trees and recent transplants are the most in need of extra irrigation. According to SacTree experts, young trees need an extra 10 to 15 gallons of water a week in summer to get established and put down deep roots. The simplest way is to use a bucket with a hole in it.

The bucket method – applying water via a 5-gallon bucket – allows water to soak in slowly even in Sacramento’s heavy clay soils. If you just pour 5 gallons of water on the ground next to the tree, it will run off instead of soaking in. With a hose, it’s just a guess how much water you’re applying.

SacTree staff experimented and found a single 1/8-inch hole – located on the bucket’s side about 1 inch above the bottom – was most effective in delivering water at just the right rate. On the bottom, the hole got clogged with dirt. Multiple or bigger holes, the water drained too fast.

How do you use a bucket with a hole in it? Cover the hole with duct tape, fill the bucket, put in place, then remove the tape.

Place the bucket close, within a foot of the trunk, to newly planted trees; their root ball still hasn’t spread out. Alternate sides with each bucket application. As the tree grows, move the bucket farther away from the trunk. The feeder roots that need the extra water most are located along the dripline at the edges of a tree’s canopy.

In the first year, give a young tree an extra 5 gallons two or three times a week, SacTree recommends. In the second year, make it 10 gallons once a week. At three years, increase the extra water allowance to 15 gallons but apply it every other week.

Mature trees benefit from extra irrigation, too. Instead of a bucket, use a soaker hose encircling the tree at its dripline and set a timer for one hour. Do that once a month.

Here are more tips to help your trees through the heat of summer:

* Irrigate thoughtfully. Check soil moisture with a probe or moisture meter before automatically turning on the sprinklers. Trees prefer deep, infrequent irrigation; it encourages deep roots.

* Remember to water trees at their dripline – the farthest reach of their foliage – and not their trunks; their thirsty roots are at that outer edge.

* To retain moisture during hot summer months, make sure to mulch. Binck recommends wood chips such as those available free from SMUD. Leave a wide circle around trunks to avoid crown rot.