Christmas lights are up and temperatures are dropping. Winter is here! You might be ready to retreat indoors for a reprieve from the chilly weather, but what about your trees and shrubs? They are dormant, but they still have needs. Find out why winter watering is essential and how to give your plants and trees what they need to survive the winter.
Which Plants and Trees Need Special Attention During Winter?
All trees, plants, and shrubs can benefit from winter watering and pruning but there are certain species that need extra care and attention. Denver is known for having harsh, cold and brittle winters and the health of some plant and tree varieties can be put at risk due to drought injury.
The dry periods during Denver winters can be hard on these trees and their exposed root systems. Plants like European white and paper birches, Norway, silver, red, Rocky Mountain and hybrid maples, lindens, alders, hornbeams, dogwoods, willows, and mountain ashes all have shallow root systems. This means these plants and trees need proper watering and extra attention.
Many people assume that evergreens don’t need much care or supervision during the winter months, but this is actually untrue. Colorado State University suggests that Evergreen plants like spruce, fir, arborvitae, yew, Oregon grape-holly, boxwood, and Manhattan euonymus all need a regular winter watering routine to thrive.
Perennials and woody plants are susceptible to the winter freezing and thawing because they often lack ground cover. This process opens cracks in the soil and the plant roots are vulnerable to the freezing cold. Extra mulch and watering can protect these plants.
Keep an eye on these particular plants and tree varieties this winter, and consult one of our arborists for more winter care strategies.
Winter Watering Best Practices
Winter watering is definitely a must, but you’re probably wondering how much and how often do I need to water? And, do I need any special watering tools? Not to worry! Winter watering is fairly easy and simple. Follow these guidelines and tips from the Boulder Parks and Recreation Department:
- Water your deciduous and evergreen trees up to two times a month between October and March.
- Check soil moisture levels around the dripline of the tree to determine how much water is needed. To accurately determine soil moisture, dig down at least 4-6 inches.
- Water during the day when temperatures are above 40 degrees to allow the water to soak in before freezing night temperatures. Do not water if soil is frozen. Hand watering, soaker hose or drip applications are allowed up to two hours per area with no day or time restrictions.
- Soaker hoses, soil needles or hoses with a soft spray attachment can be used to water trees in the winter. Do not turn on your irrigation system to water your trees.
- How much water your tree should receive depends upon the tree size. A general rule of thumb is to use approximately 10 gallons of water per inch of trunk diameter for each watering. Measure trunk diameter at knee height. General formula: Tree Diameter x 5 min. = Total Watering Time
- The most important area to water for deciduous trees is within the dripline (from the trunk to the outer edges of the tree’s branches). For evergreens, water 3-5 feet beyond the dripline on all sides of the tree.
- Maintain mulch 4 inches deep around trees and shrubs to retain moisture. Pull mulch back from the tree trunk. Mulch is available free to Boulder residents from Western Disposal.
Caring For Newly Planted And Established Plants This Winter
Another type of plant that will need special watering this winter is any newly planted tree on your property. Highly susceptible to drought injury, newly planted trees are still trying to get established. It typically takes a year to establish each inch of trunk diameter for a young tree. These new trees are working hard to grow and need regular watering to keep up with the nutrients they are trying to produce. Newly planted trees have the best water uptake when the water is allowed to soak into the soil slowly to a depth of 12 inches.
Colorado State University recommends these methods for watering trees:
- Deep-root fork or needle
- Soaker hose
- Soft spray wand
- Apply water to many locations under the dripline and beyond if possible.
- If using a deep-root fork or needle, insert no deeper than 8 inches into the soil.
- As a general survival rule, apply 10 gallons of water for each diameter inch of the tree. For example, a two-inch diameter tree needs 20 gallons per watering.
- Use a ruler to measure your tree’s diameter at 6″ above ground level.
Similar to newly planted trees, newly planted shrubs need significantly more water than established shrubs. This includes any shrub that has been planted for less than a year. However, during extremely dry winters all shrubs will benefit from watering from October through March. Mulching well around new shrubs at the onset of winter will also help them retain moisture and protect their root systems. Follow CSU’s expert guidelines for caring for newly planted and established shrubs:
- Apply 5 gallons two times per month for a newly planted shrub.
- Small established shrubs (less than 3 feet tall) should receive 5 gallons monthly.
- Large established shrubs (more than 6 feet) require 18 gallons on a monthly basis. Decrease amounts to account for precipitation.
- Water within the dripline of the shrub and around the base.
- Bare root plants require longer to establish than container plants.
- Perennials transplanted late in the fall will not establish as quickly as those planted in spring.
- Winter watering is advisable with late planted perennials, bare-root plants, and perennials located in windy or southwest exposures.
Benefits of Winter Watering
Watering is part of our regular tree and shrub care routine during spring and summer to prevent drought, but many people don’t realize that watering during a plant’s dormant season is just as beneficial. Root development occurs during dormancy and is especially active in newly planted trees and shrubs. Steady winter watering helps prevent dehydration and premature death in young plants and trees.
Winter watering can really be a lifesaver for your trees! Although trees are dormant, they aren’t just sleeping all winter long. While you lounge on the couch and watch hallmark movies this December, your trees are growing their root systems. They require added moisture to stay alive and thrive. You may have dressed your trees up with outdoor lights, but what they really want this Christmas is more water!
Winter temperatures in Denver are notorious for fluctuating. Keep a watchful eye on the weekly forecast and check your soil conditions to determine if more watering is needed. During an unseasonably warm or dry winter, even hardy established trees need supplemental watering.
Along Denver’s Front Range drought are a regular occurrence and there is not always enough snow cover to provide ample moisture to the soil. Denver is naturally semi-arid and relies on irrigation to promote much of the beautiful trees that are part of its landscapes. Don’t count on nature to provide enough water for your plants and trees this winter. Doing your part and committing to winter watering will help keep the Denver landscape looking amazing come spring.
Evergreen trees benefit greatly from winter watering because they can lose water throughout the entire winter season. They keep their needles, but high winds can strip water from them, drying them out. Dryness results in brown, brittle needles that shed and sometimes this can affect the entire tree. Winter watering will keep your evergreens lush and vibrant.
Of all varieties, Deciduous trees are at great risk during the winter from dying. Their shallow root systems grow slowly throughout the winter and they often lose much-needed water through their twigs. Proper watering can prevent branch dieback and chlorosis that won’t show up until spring.
Give your trees the best gift this holiday season and give them all the benefits of winter watering!