Close of the Year Tree Services

Trees are large, tall, and immovable. They have no choice but face what our weather throws at them in the winter. Trees adapt well to cold weather if given time to harden. However, abrupt, unexpected polar plunges and winter droughts in the Denver area injure and sometimes kill trees. One way for homeowners to help their trees survive our harsh climate is by feeding and watering them in the wintertime. Winter is also an excellent time for pruning. Ross Tree, a local tree company in business since 1978, operates twelve months of the year and provides fall and winter tree care services throughout the Denver area. The most popular winter tree services are deep root watering and feedingwinter pruningFire Blight treatment, tree removal, and dormant oil spraying. David Boswell, Ross Tree’s General Manager, discusses winter tree services that property owners should consider in Denver.

Why Water Trees in the Winter?

Dry winters are the norm here because of Denver’s average annual precipitation is 13.4 inches. For comparison, Pittsburgh gets about three times more rainfall each year than Denver. Native grasses grow fine in the foothills, but not trees, which is why Birches, Maples, Lindens, Alders, Oaks, Honeylocust, Elms, and Ash trees benefit from supplemental watering and feeding during the fall and winter.


Denver precipitation in 2021

In the dead of winter, many people do not realize that tree root systems are active biologically, so they need feeding and watering. Watering and fertilizing in the winter months nourishes root cell tissues and allows the root ball to store food for growth in the spring. Healthy trees tend to emerge from dormancy faster and grow quicker than drought-stressed and unfertilized plants.

An excellent time for deep root watering is in the fall before deciduous trees lose their leaves. Water uptake is enhanced when leaves give off water vapor through their stomata, creating a negative vapor pressure that pulls water up through the tree’s vascular tissue. Evergreen trees, like pines and spruces, retain their needles year-round. These trees still pull water up the trunk in winter, so they need to be watered sufficiently during the fall and winter months.

What Does Tree Harding Off Mean?

ice between cells

Understanding how trees survive winter instructs homeowners on how to take care of their arbor landscape during the cold months of the year. As temperatures drop and days shorten, chemical reactions tell trees that it is time to stop growing, hunker down, and get ready for cold weather. These hormones cause leaves to fall, slow growth, close stomate, and stop nutrients flowing to the branches and leaves. The tree transport system reverses course and sends nutrients down to the root mass. The roots actively grab food and water from the ground between freezes. 

Like most organisms, trees contain water inside and around their living cells. When it gets cold, the first thing to freeze is the water between the cells. What kills tree tissue is ice which becomes sharp as water molecules rearrange themselves in geometric shapes that take up more space and rip cells walls. Tree cells that get damaged die. Enough dead cells mean a dead tree. Trees use the following organic and physical chemistry reactions to accommodate ice or keep water from freezing at the cell level.

  • Tough Cell Membranes – Tree tissues have tough cell walls that can take a beating. When winter comes, the trees’ chemical mechanisms make their cells more flexible and permeable, allowing their plasma membranes to pull away from the cell wall when ice crystals burst through the cell wall reducing damage.
  • Water Tension – Water acts funny in tight spaces at freezing temperatures. Rather than freezing, the water supercools and remains a liquid.
  • Osmosis – When the ice forms between the cells, it attracts water as it gets colder. The water moves out of the tissue and joins the ice outside the cells. Osmosis also increases the concentration of intracellular solutes, which acts as an antifreeze. Conifers continue to make food through photosynthesis during the entire winter. They use solutes to guard against freezing in the winter. Winter droughts allow the concentration of solutes to get high, causing cellular failure.
  • Vitrification – Sugars in tree cells help water vitrify at temperates way below freezing. Cold temperatures turn water into a glass state that does not expand, reducing cell damage. Aspen trees growing at high elevations probably use vitrification to stay alive in Colorado during the winter.


Watering Trees in the Winter

According to Denver’s City Forester, trees need 10 – 20 gallons of water for every inch of diameter. Most homeowners do not have the time or equipment to handle the needs of larger trees, so we suggest that homeowners call a professional tree company, like Ross Tree, for large deep root watering jobs.

According to David Boswell, Ross Tree General Manager and arborist, “Surprisingly, the ground rarely freezes in the Denver area, which allows us to offer deep root watering and feeding during the cold months of the year. Typically, we have warm temperatures before and after snowstorms that soften the ground. Also, snow cover insulates the ground keeping the heat from leaving the soil. We like watering and feeding trees with snow on the ground because we can visibly see our injection spots. As the snow melts, it forces the adjuvant mix deeper into the dirt, improving the trees’ uptake. Sometimes the north side of homes stays frozen. In that case, we would reschedule for a time when it is warmer so we can get the probe into the ground.”

Drought injures the root systems of trees. Affected plants may appear perfectly normal and may resume growth in the spring. Or they die back with dead branches or do not leaf out in the spring. Trees weakened by drought become susceptible to insect and disease problems. Below are signs of drought tree distress:

  • Trees turn colors and shed leaves prematurely.
  • Shoot growth appears at the bottom of a trunk.
  • Winter kill appears throughout the crown of the tree.

plant health care truck

Deep Root Watering

Ross Tree uses subsurface probes to distribute water throughout the top 12 inches of soil surrounding a tree’s root system. Most of the water-absorbing roots are around the drip line, so we concentrate our deep root watering effort directly under the outer tips of the branches and slightly beyond. There is no need to water around the trunk since there are no water-absorbing roots in this area. To get the best results, the Ross Tree crews use a deep-root fork or needle and force water down to a depth of 12 inches. Ross Tree has the equipment to water and fertilize the largest trees in Denver. Our plant health care trucks bring all we need to the job, saving our customers time and money. Below are the wintering watering guidelines provided by the Colorado State Forest Service.

  • Water slowly: Deep root watering allows deep soil penetration and is cost-efficient.
  • Lawn trees: Trees located in irrigated lawns generally do not require additional water in the summer. After the system is shut down, we recommend supplemental watering during extended dry winter periods.
  • Mulch: Mulch reduces tree stress by retaining soil moisture and saving water. Apply 4 inches of mulch onto bare soil within 2 to 3 feet from the trunk base. Make sure the mulch does not touch the tree trunk.
  • Winter Watering: Water only during the day and when air temperatures are above 40 degrees allowing the water to soak into the soil.
  • Newly planted trees and shrubs: They require more water than established plants and should be watered twice per month between October – March.
  • Water a wide area: Tree root systems spread two to three times wider than the tree’s height. The most absorbing roots are in the top foot of the soil. Soak the entire area within the drip line.

Deep Root Tree Fertilization

In yards, trees compete for nutrients with turf and shrubs. Also, some trees grow poorly in Denver’s clays soils because of lack of aeration, which decreases the root systems’ ability to replenish water loss brought about by our dry climate. Ross Tree recommends deep root fertilization three times a year to give trees need extra nutrients to reach their full potential and offset the lack of natural nutrient recycling in a manicured setting. Below are signs that trees need fertilization:

  • Stunted growth: Clay soils stunt tree growth, and fertilization reverses this condition.
  • Chlorosis: Maples and some Oaks are prone to this disease. Affected trees cannot absorb iron from the soil, so their leaves turn yellow. Discoloration signifies that trees are not getting enough nutrition. 
  • Newly planted: Freshly planted trees are low on nutrients and need fertilization to keep them growing.

Ross Tree uses Essential Plus for deep root fertilization. It is a 100% natural soil amendment derived from potassium hydroxide, organic proteins, sugars, and Humic acid. The fertilizer replenishes soils depleted of organic matter, helps alleviate soil compaction, and provides a food source for beneficial soil microorganisms. The deep root injection:

  • Enhances beneficial microbe populations.
  • Provides microbes with a vital food source.
  • Improves root growth.
  • Allows oxygen to penetrate the root zone and encourages fibrous roots to colonize.

Chapstick for Trees

Colorado is known for its 300 days of sun. Desiccation is an injury caused when the loss of moisture by the tree leaves exceeds the water taken in by its roots. Evergreens and some shrubs in Denver are especially susceptible to windburn and sunscald. Ross Tree applies wax-like anti-transpirants to prevent plants from losing moisture through their foliage and help them look their best throughout the year. It is like chapstick for plants.

winter tree removal in Denver

Fall and Winter Pruning

Did you know that trees set their leaf and flower buds in late summer? That being the case makes winter an excellent time for tree pruning because trees are dormant and not growing. The benefits of tree pruning when the leaves have dropped are as follows:

  • Easier to evaluate tree structure: After the leaves drop, it is easier to see your trees’ branch formation and identify any problems. Winter pruning benefits younger trees and sets them up for a successful growing season.
  • Better looking trees in spring: After a winter pruning, the tree directs energy to fewer branches, which improves the overall vigor of a tree. The buds on the remaining branches produce healthier leaves, fruit, and limbs.
  • Saves money: Frozen ground allows heavy equipment to be staged next to the tree, so the job goes faster, lowering job costs and producing better outcomes.
  • Less tree stress: Research shows that pruning during dormancy and before buds break in spring leads to faster wound closure. Healed wounds keep out destructive insects and pathogens.
  • Avoids spreading disease: Many common trees diseases are inactive in the winter, so cold days are a perfect time to prune out dead wood, cankers, and other parts of the affected trees.
  • Prevents winter storm damage: Winter pruning removes any branches most likely to break to make trees less susceptible to snow breakage.

Ross Tree embraces ANSI pruning standards approved by the Tree Care Industry Association. Below are pruning types commonly done in the cooler months of the year.

  • Structural Pruning – Structural pruning favors a dominant leader promoting tree growth around a single trunk. Weaker tree limbs get trimmed back to their strongest point or removed. Structural pruning makes trees less susceptible to mechanical breakage caused by Denver’s wind or snowstorms.
  • Rejuvenation Pruning – Bare trees show their structure, which makes trimming easier. Also, trees pruned in the middle of the winter have time to heal, with new spring growth covering any bare spots in the canopy.
  • Safety Pruning – We cut out any dead, injured, or diseased branches that may become safety hazards to people or buildings below them.

Cold Weather Damage to Trees

winter tree damage

When temperatures drop slowly, the tree has time to harden and acclimate to the freezing temperatures. The sap flows into the root system, and the tree adds tissue to toughen up and protect its branches and trunks as winter approaches. However, over the last two years, Denver experienced sudden drops in temperature in October. During a warm day, the tree cells beneath the bark become active. At sundown, the temperature suddenly drops, and the cells do not have the time to return to dormancy and freeze, injuring the tree. Below are the types of freeze damage:

  • Winter Kill – Symptoms of “winter kill” include brown or black discoloration or branches and leave limpness. Pruning in the winter takes care of any damage caused by polar plunges in the fall.
  • Sunscald – Sunscald affects tree trunks and large branches. Over time, the bark breaks down, exposing the tree to the elements.

Ross Tree uses light-colored wraps for winter protection. We wrap the tree in an overlapping fashion from the ground to the first branch. Homeowners should remove the wrapping after the last frost in the spring to avoid mold formation. Well-maintained trees that have healthy roots systems snap back faster from polar plunges.

Fire Blight Treatment

fire blight lifecycle



The bacterium, Erwinia amylovora, causes Fire Blight. When the temperature gets in the 60s in the spring, the bacteria multiply rapidly, forming a bacterial ooze that forces its way onto the bark surface. Insects become unwilling carriers of the disease as the ooze sticks on their bodies, and they visit other parts of the tree or other apple or pear trees in the neighborhood. Rain and hail splashes can also spread the pathogen to other parts of the tree. Later in the spring, the blossoms on affected trees appear water-soaked and turn brown quickly. Dead trigs and leaves curl up and form a Shepards’s crook, a telltale sign of Fire Blight. Winter is a good time for Fire Blight treatment because there is no need to sterilize the tools between cuts. For more information about Fire Blight, click here to view Ross Tree’s Fire Blight Handbook.

What Tree Insects Can Be Treated in the Winter?

Any insect or invertebrates, such as scales, mites, and aphids that overwinter as eggs can be treated with dormant oils in the winter. Scale insects suck sap from plants similar to aphids. However, scales have protective waxy covering and waxy egg sacks. Aphids are the most widespread insects in Colorado. Some species are significant trees pests, reducing plant vigor, producing leaf curl, or secreting copious amounts of honeydew. Spider mites are not insects but are invertebrates like spiders and scorpions. These pests feed on plants, using their mouthparts to break into the upper cell layers and suck the plant sap. Dormant oils suffocate the eggs of these tree pests. Homeowners who had a previous heavy infestation of these insects should consider using dormant oils to treat these tree pests in the winter.

  1. Oystershell ScaleLepidosaphes ulmi

    The Oystershell Scale feeds on the phloem of trunks and branches. Heavy infestations produce stunting, foliage yellowing, and bark cracking. Branch dieback is a common symptom of scale injury, and sometimes scale-infested trees get Cytospora cankers.
     Oystershell scale in Denver

  2. Pine Needle Scale Chionaspis pinifoliae

    Pine needle scales feed by sucking sap that causes needles to discolor around the feeding site. Heavy infestations cause premature needle drop and kill branches and even young trees. Pine Needle Scale targets Mugho Pines in Denver. 

    Pine Needle Scale in Denver

  3. Giant Conifer AphidsCinara species

    Giant Conifer Aphids adults are about 1/4 inch in length, long-legged, and brownish-green in color. Their eggs are shiny and black, resembling miniature jelly beans, laid in rows on twigs and needles. These aphids usually feed in large groups on the sap of twigs and branches. Heavy infestations cause foliage to yellow and produce large deposits of honeydew. 
    Giant Conifer Aphids in Denver

  4. Leaf Curl Ash Aphid Prociphilus fraxinifolii

    Feeding by this aphid causes Ash leaves to curl and thicken. Some adults form wings in July and fly around in the fall to other trees. 
    Ash leaf curl aphids in Denver

  5. Boxelder And Maple Aphids – Periphyllus species

    These aphids are about 1/10 inch long, with yellowish-green marked brown bodies with spine-like hairs and hairy antennae. Heavy infestations cause leaves to drop and sometimes totally defoliate affected trees. Copious amounts of honeydew drop on cars, patio furniture, driveways, and sidewalks beneath infested trees. 
    Maple aphids in Denver

  6. Honeylocust Spider Mite Platytetranychus multidigituli

    Heavy infestations of Honeylocust Spider Mites turn Honeylocustleaves an off-yellow color and causing premature leaf shed. Honeylocust Spider Mite targets drought-stressed trees planted along roads, parking lots, and other hot, dry sites.
    honeylocust spider mite in Denver

  7. Spruce Spider Mite Oligonychus ununguis

    The Spruce Spider Mite is very common and damaging to spruce and junipers in Colorado. Highly infested trees become brownish gray and sometimes defoliate.
    spruce spider mite in Denver


Tree Removal

winter tree removal in Denver

Winter is a great time to remove trees because when the ground freezes, heavy equipment can be staged next to the tree, causing minor yard damage. Ross Tree evaluates the tree and provides a quote to the property owner.

Believe it or not, fall and winter are active tree service months. For an appointment, click here to fill out a tree service request form or call 303-871-9121.