Video

Dry times can mean trees need a little TLC

The importance of watering your trees during winter dry spells.

It has been warm and dry across Colorado this winter, and landscape experts remind us that when Mother Nature holds back on the moisture, it’s important to give your trees a good drink to help them get through the dry times.

Use a hose or bucket to water trees. Due to this year's drought conditions and the need to conserve our water supplies, delay turning on automatic sprinkler systems until mid-to-late May. And then, watering two days per week should be sufficient for your lawn for most of the summer.

Winter watering is important for your trees because it helps prevent root damage and encourages new growth in the spring. It’s especially critical for newly planted trees. That’s because they’re still trying to establish their roots.

Do's and don’ts

First off, winter watering might be needed between October and April. And, before you pull out the hose, here are a few important do’s and don’ts to keep in mind:

Do:

Water only when there has been no meaningful rain or snow for two to three weeks.
Water at midday and only when the temperature is above 40 degrees.
Use a timer when watering so you don’t forget the water is on.
Disconnect your hose from the spigot after watering so it doesn’t freeze.

A man squats near an outside hose faucet with a green hose rolled up beside him. — Always remember to disconnect your hose from the spigot after watering in winter so it doesn’t freeze at night. Photo credit: Denver Water.

Don’t:

Don’t water if there is snow on the ground or in the forecast.
Don’t water if the ground is frozen, because the water won’t soak in.
Don’t use your underground sprinkler system. Keep this turned off until mid-to-late May so your pipes don’t freeze.

Your plants could use a drink during dry winters too! Learn more in this TAP story.

Understanding the drip line

An important part of watering trees is understanding the tree’s drip line.

The drip line is basically a circle around the outer branches of the tree where the raindrops fall naturally. This is where tree’s roots get most of their water, so make sure you are watering in this area.

An illustration of a green tree showing that its roots extend far beyond the tree canopy. — The drip line is the area under the outer branches of the tree where rain drops fall naturally. This is the area where the roots get most of their water. Image credit: Denver Water.

Watering guidelines

As in all gardening, when it comes to watering, keep in mind that the times and amounts are recommendations and not hard science as every plant, watering device, landscape and person is different.

Having said that, the general rule of thumb from horticulture experts is that for each watering session, trees need about 10 gallons of water per 1-inch diameter of the trunk.

For example, if a tree is 2 inches in diameter, you’d give it 20 gallons each time you water it. A 3-inch diameter tree would need 30 gallons each time you water it.

How to water

Now let’s look at a couple of watering methods.

For newly planted trees, our partners at The Park People say a simple method is to use your hose and let the water run at a slow trickle at the base of the trunk for about 30 minutes. Be sure to move the hose around the drip line a few times to make sure you’re reaching all the roots.

Remember to check in on the tree during this time to make sure the water is still soaking into the soil and not running onto pavement or the street.

A hose waters the base of a small tree surrounded by mulch. — A simple method to water newly planted trees is to place a hose over the root ball and run the water at a trickle for about 30 minutes. Photo credit: Denver Water.

Soaker hoses are another great way to water your trees. These are hoses with tiny holes that let the water slowly leak out. They work well because you can stretch the hose around the tree’s drip line.

As for how long to run the soaker hose, the Colorado State Forest Service says that soaker hoses emit about 10 gallons over 20 minutes.

So, using our rule of thumb mentioned above, that means a 2-inch diameter tree would need the soaker hose on for 40 minutes. And for trees 6-inches in diameter or larger, you can run the soaker hose for 120 minutes. Again, watch to make sure water isn’t running onto the sidewalk or street.

A black soaker hose forms a wide circle around a small tree. — Soaker hoses work well for watering trees because you can wrap them around the tree while the hose slowly releases water, allowing it time to soak into the ground. Photo credit: Denver Water.

Another good option for watering established trees is to use a sprinkler that attaches to a hose. Set it up around the drip line to get the roots and run it in several locations around the tree.

To figure out how long to run the sprinkler, set up some cups and run the sprinkler until you’ve got about half an inch of water. Remember to take note of that time for future watering so you don’t have to set the cups up again.

Five red plastic cups circle a sprinkler that is watering grass. — Set up plastic cups around the sprinkler and run the water until you have a half inch of water in the cups. This method determines how much time it takes to water the tree. Photo credit: Denver Water.

Experts say that using sprinklers to water your trees provides the additional benefit of also watering your lawn at the same time. Winter watering helps prevent root damage and dehydration and also helps fend off “mites” that can kill your grass.

A man moves the hose connected to a sprinkler that is watering grass. — Manual sprinklers should be placed around the tree’s drip line and moved to several locations during each watering session. The sprinklers also help water grass during dry spells. Photo credit: Denver Water.

Key tips:

Watering by hand does take time, so be sure to prioritize which trees to water if you have limited time.
Always focus on newly planted trees first as they are still establishing their roots.
Remember that evergreen trees are still active in winter.
Trees that are in wind-prone and south-facing parts of the yard dry out faster, so be sure to help them out when it’s dry.

For more information about watering trees, check out CSU Extension’s helpful video.

For more general information about watering plants in the winter, check out this Denver Water TAP story and video we did with a CSU expert.

Thanks to all of Denver Water’s expert partners for sharing their expertise on winter watering: Colorado State Forest Service, CSU Extension, Denver Botanic Gardens, Plant Select, Resource Central and The Park People.