Colorado Tree Care Through all Four Seasons

As a mile-high homeowner, it’s important to know the tips and tricks for Colorado tree care. Not only do your trees add beauty to your property, but they can also provide essential shade and help improve air quality. However, if you’re not familiar with proper Colorado tree care practices, you could be doing more harm than good. Not to mention that we experience all four seasons here – and so do our trees! In this article, we’ll discuss the top dos and don’ts of tree care in our beautiful state through each of the four seasons. 

Spring Colorado Tree Care

Following winter, your trees and shrubs work hard to bounce back and produce healthy new growth. Looking forward to seeing your landscape turn lush green this spring? Give your trees the boost they deserve with well-timed and properly, professionally executed fertilization. Reap the benefits for the spring, summer, and fall months.

Time to Fertilize

For the best Colorado tree care, apply fertilizer when trees need it and when they can absorb the nutrients with their roots. The prime times for fertilization are spring and fall when the weather is reasonable, the trees have active root growth and a decent amount of soil moisture. Conditions are highly conducive to plant growth and that’s why it’s so important to fertilize when the conditions are right.

Fertilization is not recommended in the frigid cold of winter because plants are often unable to absorb the nutrients due to frozen ground and the stressful weather conditions.

Moreover, a common misconception is that fertilizer is tree food. Through photosynthesis, trees and shrubs naturally produce their own adequate food supply. With that in mind, the photosynthesis process can be hindered by poor soil, lack of available nutrients, drought, and other adverse conditions. Fertilizer acts as a supplement, or vitamin, to trees and shrubs. It’s composed of minerals and nutrients that supply the ingredients required for successful photosynthesis and healthy growth. 

Fertilization Methods

Deep-Root Feeding

Soluble liquid fertilizers are injected below the soil surface with this method of application. Deep-root injection can be highly effective for producing quick green results. Although it’s called deep-root feeding, 80-90% of tree roots are in the top 8-16 inches of soil, so the fertilizer is applied in a shallower area. One benefit of this method is that liquid fertilizer is more soluble than granular and consequently reaches the root zone more rapidly.

Trunk Injection

With this method, micronutrients are injected directly into the tree trunk. The injection can correct micronutrient deficiencies caused by elevated pH and high nitrogen levels found in the soil. It is possible for the tree to form a wound at the injection site which can become infected with fungus, and for this reason, it’s often only used as a last resort.

Foliar Feeding

If you’ve determined that your trees need micronutrients such as iron, manganese, and zinc, this might be the perfect application for you. This method is very effective for replacing the micronutrients that are unavailable in soil with high pH. Foliar feeding uses a spray mixture that helps to increase the micronutrient uptake.

Drill Hole Fertilizing

Small holes are either dug or punched in the soil and granular fertilizer is inserted into these holes. The hole pattern is scattered, reaching beyond the dripline and around the tree. One issue that can occur with this method is high concentrations of fertilizer in relatively small areas. In some instances, the high salt concentration may burn roots at the fertilization site. Due to this, our team of certified arborists do not generally recommend this method and would only use this as a last resort.


The spike fertilization method is important to mention because we do recommend drill hole fertilizing over spike fertilizing. Spike fertilizers are readily available at your local hardware store and, unfortunately, aren’t effective enough to be worth using. While drill hole fertilizing may have high concentration in a small area, spike fertilizing has a super high concentration in an incredibly small area. Save your time and money and invest in a different fertilization solution.

Spring Pests

After winter, spring pests are on the verge of waking and becoming active. There’s a small window of time to act and take preventative measures to control these pests before they invade. Luckily, there are safe and effective treatments to manage and control these spring pests. Don’t let the Japanese beetles and aphids ruin the quality outdoor time you crave for your spring and summer.

Japanese Beetles

Japanese beetles were first recognized in Denver in the early 1990s. Since, the beetle infestation has grown enormously, becoming a fixture in the Colorado landscape. Despite the county’s best efforts, the Japanese beetle population continues to grow and spread each year. Japanese beetles are easily recognizable by their metallic green shell. While these beetles may look pretty, they are considered one of the most relentlessly destructive urban pests in the United States.

Here are some quick facts on the Japanese beetle from the Colorado State University Extension:

  • Japanese beetle adults chew flower blossoms and leaves of many commonly grown plants.
  • Japanese beetle larvae are a type of white grub that feeds on the roots of grasses.
  • Adults are best controlled by handpicking or by use of certain insecticide sprays.
  • Japanese beetle traps can capture many adults, but do not reduce damage to nearby plants.
  • Japanese beetle larvae can be controlled with certain insecticides or by insect parasitic nematodes.

There are 300 plant varieties that the beetles crave and prey on, but lindens are on the top of their list. 


There are over 350 species of aphids! They are tiny, are only a few millimeters long, and range in color from light yellow to dark brown. Many are harmless, but it’s important to note that the rosy apple aphid, woolly apple aphid, and leaf curl ash aphid are plaguing Denver’s trees. Ash, Apple, and Crabapple Trees are endangered by these pests. Not only do aphids wreak havoc on the trees they infest, but they also attract other harmful pests.

Signs of an Aphid Infestation and Treatment Options
  • Woolly aphids obscure their body by covering themselves with waxy threads. Look for limbs covered in a waxy film. You will probably find a cluster of aphids there!
  • Sticky leaves or stems are a sign of honeydew left behind by aphids.
  • Fungal growth is a result of aphid honeydew production.
  • Leaves will begin to yellow, look misshapen, curling, or stunted.

Soil injection insecticides are very effective in Colorado tree care for fighting aphid infestation. Rapid systemic soil injections are an environmentally safe soil injection insecticide. They have a solution that provides rapid results, delivering systemic control of many key shade tree pests. This is also a highly effective tool for management of both Japanese beetles and aphids. One application of a rapid systemic soil injection will give 30 days of efficacy for insect larvae.

Here are details on how a rapid systemic soil injection is typically applied:

  • Application Method: Pull back landscape mulch, landscape fabric and surface organic matter prior to making soil applications to ensure solution is delivered to the mineral soil. Measure the diameter of the tree at breast height (DBH), 4’6” above the soil line. For multi-stemmed trees and shrubs, use the cumulative diameter of individual stems at soil line instead of DBH.
  • Application Timing: Make applications to actively growing plants just prior to or when insects first appear. Repeat applications every 2 weeks as needed.

Rethink That Mulch Volcano

Adding new mulch each spring is a habit that most of us are in, but there’s more to it than just spreading a few bags of fresh mulch around your landscaping. You need to make sure you’re not creating mulch volcanoes.

Mulch volcanoes happen when you pile mulch too high around the base of your tree and looks exactly like what its name implies. This can suffocate the tree and prevent it from getting the oxygen and water it needs. When the mulch cuts off access to oxygen and water, your tree may suffer from root rot or other problems.

It can also encourage pests and diseases, which can further damage your tree. Mulch volcanoes attract pests because the mulch provides them with a hiding place and a source of food. Tree disease tends to breed around mulch volcanoes because the moist, humid conditions are ideal for infection and growth.

To avoid creating a mulch volcano, make sure to keep the mulch several inches away from the tree trunk, and no higher than two to three inches thick. This will allow your tree to get oxygen and water without suffocating it.

Summer Colorado Tree Care 

Less Is More

In most cases, all you need to do in the summer is keep an eye on your trees, let them grow, and enjoy them. Most of the maintenance work is done in spring and fall. So pull up a lawn chair, hammock, or just a patch of grass and take in the shade. 

Special Circumstances

Extenuating environmental circumstances put all types of trees under stress during the summer months. 

Drought is one example of this. Subsequently, trees experiencing a drought need an extra boost from fertilization to help them recover. Drought causes stress on trees because they cannot take up enough water to meet their needs. This causes the leaves to wilt and the tree to stop growing. Eventually, the tree will start shedding leaves to conserve water. If a drought is severe enough, it can kill a tree.

Avoid heavy pruning of fully mature trees in the middle of summer. When it’s hot, it’ll be difficult for them to recover. Use an open hose over the root zone once a week, or once every two weeks minimum, to give roots a nice dose of extra water in the middle of summer, when they’re really sweating to death and experiencing some form of heat exhaustion. 

Fertilize Only if Needed

As stated earlier, fertilizing in spring and fall is the best time to do so; however, Denver sometimes experiences a winter drought. Summer fertilization can become particularly important because of the extra strength from nutrients that trees need to recover after a particularly dry winter.

Fertilizing in just the spring and fall will help your trees thrive year-round, but if you want to aid their recovery from the environmental stress from the past year, then we would recommend adding fertilizer to your summer care. Here are a few reasons why:

  • The warm summer weather and longer days stimulate growth.
  • Fertilizing in summer helps trees develop a strong root system before winter sets in.
  • Fertilizing in summer helps newly transplanted trees become established more quickly and can give mature trees the nutrients they need to produce a strong flush of new growth.
  • Summer is also an ideal time to correct any nutrient deficiencies that may have developed during the previous growing season.

Fall Colorado Tree Care

Who doesn’t love fall? It’s the season of football, pumpkin patches, corn mazes, apple cider, bonfires, and pumpkin spice everything. The order of importance of that list varies from person to person, but you get the idea. It’s also the time for raking leaves and getting your trees ready for winter. Yes, the weather may be in the 70s across Denver, but a quick plunge into winter can be only days away.

Now that your trees have shaken their leaves loose, here’s the best way to show your trees some love before winter.

Rake Up Most of Your Leaves

Firstly, remember that when it comes to Colorado tree care in the fall, “leaves on the ground let diseases stick around.” Thick piles of leaves can invite snow mold to infest your lawn. Other diseases can also make their way from dead leaves to the root system of your trees.

Wait a minute… didn’t you say “most” of your leaves? That’s a good point. If you want a perfectly manicured lawn, track down every one of those leafy fugitives and send them packing. However, leaving a few leaves isn’t bad for your lawn. In fact, letting a few random leaves disintegrate into your lawn can be good fertilizer. If you’re going to mow again, your mower blade will shred small amounts of leaves with each pass and spread them on your lawn to break down easily.

Keep Watering!

Your trees may not have their leaves, but they’re still drawing significant amounts of nutrients from the soil. It takes a lot of work to get rid of leaves and your trees are thirsty! Use a subsurface probe to distribute water throughout the top 12 inches of soil surrounding your tree’s root system. This is the area where your tree needs the most water.

Fertilization is a Must for Fall Tree Care in Colorado

Guess what? If your trees are thirsty, they’re also hungry! Even though your tree is drawing nutrients from the soil, it needs a kick start of good vitamins to help protect its vascular system heading into winter. We recommend using a slow-release tree fertilizer to give your tree the maximum time frame to absorb crucial nutrients. Check out our tree fertilization section to learn more.

Winter Colorado Tree Care

Winter Tree Trimming

Once all the leaves are gone, it’s time for a certified arborist to give your trees a nice haircut. Having no leaves present means an arborist can see the exact structure of your tree’s branches and limbs. A certified arborist can identify and remove branches that are damaged or diseased. Corrective pruning will help retain your tree’s natural shape and prevent snow and ice damage throughout the winter. 

Landscape and garden projects may be far from your mind around this time of year, but winter tree trimming is essential to help trees grow healthy, happy, and strong come springtime. One of the best opportunities to trim trees in Denver is during the winter months. Here’s why:

  1. During the winter season, trees go into a state called dormancy. 
  2. During this time, trees naturally go to sleep, take a break, and stop producing new growth.
  3. Trimming during the wintertime will not cause the tree any stress and will encourage new growth to come in the springtime.
  4. Early winter/late fall is the perfect time to trim fruiting and flowering trees. This allows them to use more of their energy to produce fruit or flowers come springtime.

Like animals who hibernate, winter is a tree’s time to rest and recharge. Getting your annual trimming and pruning accomplished during the winter will cause less stress for your trees. The timing provides optimal wound closure and time for healing. A stress-free tree is a happy tree!

Late winter is a great time to prune, contain or rejuvenate overgrown shrubs and trees as they’ll be able to recover quickly in spring with new growth. This will also minimize the amount of time you’ll spend looking at a plant that looks like a bunch of sticks after rejuvenation pruning.

We recommend hiring a professional arborist who will know the exact time and way to tend your trees. That said, we understand that there are plenty of homeowners who want to venture into pruning their own trees. If that’s you, we put together a guide for DIY tree trimming

Winter Tree Trimming Tips

  • Clear the area of any debris or unnecessary objects in the immediate vicinity. 
  • Try to create a clean, smooth surface for work.
  • If your property lacks adequate space (clearance from home) or level ground, share your concerns with our arborists to create a good plan of action for everyone’s safety.
  • Consider any recent storm or flooding. A significant amount of water can make the ground softer than normal and can expose surface-level roots that are easy to trip over and can be a nuisance for ladders. 
  • Take a thorough walk around the base of your tree to make note of any roots or big rocks that may get in the way.
  • Examine your tree’s trunk. If there’s any structural weakness, your tree may be compromised and in need of removal. Make note of any unusual signs or details you notice as you inspect your tree.
  • If a recent storm moved through the area, branches may be broken, roots exposed, or the bark may be displaced. In each of these three cases, your tree may be at heightened risk of contracting a destructive disease.
  • Thin out branches to create stronger branch attachments and dense growth.
  • Prune old spurs to encourage new ones.
  • Trim branches to create an open center, maximizing sunlight to all parts of the tree.

Bonus Tip: Preserve Your Landscape

During cold Denver winters the ground freezes, which is very helpful if heavy equipment is needed to accomplish tree trimming. The cold hard earth will not be utterly destroyed in the process, and your landscape can stay intact. Overall, that typically saves time and money and produces great results. 

Year-Round Tips

Each region has unique tree care needs. For example, trees in Denver need to be able to withstand our harsh winters and hot summers. This means that they require different care than trees in other parts of the country. Denver soil is also known for being rocky and dry, which can be tough on trees.

Mastering the care for each season is a substantial milestone in ensuring the health of your trees for years to come. And if you decide that instead of investing the time you’d rather invest the coin, schedule a free consultation so our certified arborists can give you an accurate estimate. 

Pillars of Effective Colorado Tree Care

Your trees require regular maintenance! To keep them happy and healthy there are several routine tree practices you should follow with fidelity:


How much, how often, and when to water your trees properly can be confusing. The rule of thumb is 2 gallons of water per diameter inch of the tree trunk (measured at knee height).


Mulch helps retain moisture in the soil, provides nutrients, and protects tree roots from compaction. Use organic mulch like wood chips, bark, or leaves. Create a donut shape of mulch around the base of the tree extending out to the edge of the branch spread. Keep mulch several inches away from the tree trunk to avoid problems.


Trees need food just like people and other plants. Fertilizing gives them the nutrients they need to grow strong and healthy. The best time to fertilize is in the fall so the trees can store the nutrients over winter.


Pruning is necessary to remove dead or dying branches, promote new growth and shape the tree. It’s important to prune properly though, as bad pruning can damage the tree.

Happy tree parenting! From our team at Fielding Tree Care.