Tips for watering trees in Denver

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In Denver’s semi-arid climate, trees and water are both precious resources.

With a few expert tips, you can preserve mature trees on your property and establish new trees that will help grow our urban canopy, diminish heat islands and combat the arrival of Emerald Ash Borer.

Does my tree need more water?

In most cases, sprinkler irrigation and natural moisture from the occasional rainstorm do not provide consistent moisture for trees in Denver. It can be difficult, however, to tell whether a tree needs additional water simply by looking at it, so follow these tips to determine your tree’s needs:

• Stick your finger into the soil at the base of your tree:

- If it easily penetrates, the tree is adequately watered.

- If it’s difficult to penetrate the dirt, the tree needs more water.

- If you observe standing water in the hole when you pull your finger out, the tree is over-watered, which can be as damaging as under-watering.

• A soil moisture meter is another option for determining a tree’s watering needs.

How much water does my tree need?

Once you’ve determined that your tree needs more water, there are some standard guidelines for determining exactly how much. Regardless of the tree’s age, a tree in a non-irrigated area needs 10 gallons of water per week per inch of trunk diameter. For example, a two-inch diameter tree requires 20 gallons of water per week. This can be spaced out over two to three days per week.

An easy way to match your watering technique to your tree’s needs is to put a hose on a low-pressure setting and put it into a 5-gallon bucket — which are commonly found at home improvement stores — then time how long it takes to fill the bucket. Once you know the timing for your watering system, start a clock and move your hose around the base of your tree.

How do I effectively water my tree?

A simple hose is the most basic tool needed to water your tree, but soaker hoses, soft spray nozzles and soil needles can help break through the soil surface. Most absorbing tree roots are found in the first 12-inches of soil depth, so be sure water is applied slowly and has time to absorb into the soil and reach these vital roots.

Adding mulch around the base of your tree is a simple and effective way to help retain moisture. A maximum mulch depth of three-to-five inches is optimal, but be careful not to let the mulch directly contact the trunk of the tree.

Additional resources

Before you begin any watering program, it’s important to get familiar with Denver Water’s outdoor watering rules, which take into account our high summer temperatures and recent drought conditions. While hand-watering trees is not restricted, we encourage following the recommended watering times of between 6 p.m. and 10 a.m. to optimize your efforts. Read more of Denver Water’s outdoor watering rules by visiting www.denverwater.org/residential/rebates-and-conservation-tips/summer-watering-rules.

The Colorado State University (CSU) Extension is also a great resource for tree care and other home landscaping needs, including seasonal watering recommendations that are customized to our unique Colorado climate. Learn more tips from CSU Extension online: https://extension.colostate.edu/topic-areas/yard-garden/watering-a-home-landscape-during-drought-7-240-2/.

Paul Cancik is an inspector with Denver Forestry

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