In Colorado, plant trees in fall for a bit of shade next summer

It has been one long, hot summer. We’ve had over 65 days with temperatures at 90 or above. Smoke from fires in Colorado and across the West showed up in August and limited time spent in the garden, except to pluck a ripe tomato for lunch. The smoke is clearing, so shake off the ash and get outside — time for fall planting, maybe even a tree or two.

One of the most important landscape investment decisions a homeowner will make is what kind of trees to plant. A well planted and cared for tree should live for 50 or more years.

Trees lower energy costs, increase property values, and have been proven to help people recover from stress. Late summer to early fall is considered by many local tree professionals and Colorado State University to be the second-best window to plant trees, right behind spring. This applies to lower elevations of Colorado.

What do you like and want from a tree? How important are the seasons of interest? There’s spring bloom, provided a late spring cold snap does not freeze the blossoms, which is common along the Front Range. Some trees bloom beautifully in the summer like catalpa, seven-son-flower and golden rain tree. How about leaf color? Solid green always works, but there are some tree cultivars with attractive maroon or purple leaves all through the growing season. Hands down, fall color is right behind spring bloom in importance to many people.

Choose a new tree wisely and avoid planting what all the neighbors grow. Variety among trees is critical for the future of having a healthy, growing green canopy around for a long time. History shows us that planting too many of the same tree is not wise — disease or insects can take out an entire tree population. Ash trees in the Fraxinus genus are not to be planted now because of the spread of the pest insect — emerald ash borer.

Will fall tree planting work for you? What are the advantages and drawbacks to consider before purchasing a tree? What are the best trees to plant in fall? Planting tips?

RELATED5 house plants that can actually survive Colorado’s dry winters

Let’s peel back the bark and answer the questions.

Fall tree planting, Yea or Nay?

A garden center deal is a deal, who can pass up plants on sale, including trees? Many garden centers put their plant inventory on sale in late summer which makes sense so they are not carried over the winter. Because gardening has become so popular this year, do not delay in checking out tree availability — selection may be limited.

If you have a tree in mind, especially one with fall color, fall is a good time to view the tree as it begins to change colors. You’ll also catch a tree that might be accidentally mislabeled as having good fall color!

Another option when purchasing a tree in fall is to temporarily winter it over outside in your landscape, and plant next spring. This is easier with a containerized tree or smaller balled-and-burlapped (b&b) tree. Simply bury the tree, container, b&b and all in the landscape in a sheltered location that doesn’t receive intense winter sun or direct reflected light and warmth from a wall (this may cause it to wake up too soon in our frequent see-saw freeze and thaw cycles — not good). Once buried with loose soil, give it a 3- to 4-inch layer of mulch to hold in moisture. Basically you are maintaining the tree-like nurseries do when they winter trees outside.

Normally, late summer through fall with our cooler weather is very conducive for tree roots to get established before winter. However

Be aware that cold snaps can happen at any time during the fall season. These sudden and extreme swings can have deadly consequences for newly planted trees and perennials (bulbs should be fine). Last fall was typical Colorado weather — warm and dry until Oct. 10 when we woke up to a chilly 18 degrees. The 2014 November cold snap is another example of a rapid temperature drop that damaged and killed many trees, not just newly planted ones.

The takeaway for fall planting: Hope the weather gradually gets colder over several weeks, giving new trees time to grow new roots. Mature trees also need a slow temperature progression to winter. Moist roots help trees (new and existing) and all landscape plants transition better to winter. Be diligent about watering new trees through the winter, at least once or twice a month if moisture is scarce. This includes trees that are wintered over in their container.

Spring planting can be challenging too, this past spring-summer is a perfect example. Any newly planted tree was subject to unusually hot, sunny days from the get-go with only a few days of rainy reprieve. Keeping the root ball area moist, but not overly saturated required steady baby-sitting. An advantage to staying at home this summer was tending to the plants.

Trees to plant in fall and spring

Some trees naturally establish better with a longer frost-free period like spring. Wait until spring to plant magnolia, American hornbeam, ginkgo, tulip tree, sweetgum, oak, American yellowwood, birch, cherry, plum, dogwood and willow.

Trees that are better candidates for fall planting include lindens, crabapples, apples, hawthorns, honey locust, Ohio buckeye and elm.

Planting conifers, also called evergreens, in the fall is not recommended. Their needles continue to transpire and unlike deciduous trees are exposed to the winter elements. Your best bet is to wait until spring.

Wait until late winter to early spring to plant bare-rooted trees and shrubs.

Planting trees: where, how and ongoing care

The first year of a tree’s life is very important. According to Clemson University, nearly 50% of trees newly planted by a homeowner die within the first year. This cannot be expressed more strongly — a new tree has to be planned, planted and set up for success from the start and maintained as it grows through its 50-plus years of life.

Choose a tree from the nursery that is visually healthy, free from mechanical damage, insects, and disease. It should not have wilted leaves. Branching should be evenly growing around the trunk. Look for a dominant, central leader, no co-dominant or adjoining, double trunks. The roots should not be girdled or circling around inside the container. Ask the staff if they will lift the root system for you to examine. Examining the roots on a balled-and-burlapped tree will be more difficult.

Before planting, ask yourself these questions

• Does the planting area have enough room for the growth of the tree above and below ground? Above ground, look for utility lines, rooflines, fire hydrants and other close by structures, trees and properties. Below ground, if structures and foundations are too close, then the roots will not have ample room to grow. Check with your local municipality for permitting and regulations for planting on city-owned tree-lawns, the area between the sidewalk and the street. The nursery tag label lists the 10-year growth height; expect the tree to grow larger in time.

• How is the drainage in the planting area — if water pools toward the tree it can easily drown. Heavy clay soils also drain slowly so amending the area may be in order.

• Have you considered your environment? Understanding the sun and environmental exposure is critical for healthy tree growth. Just about any tree would first choose an east-facing location with a slight breeze. Choose the right tree for the right location. Small, ornamental trees like redbud, serviceberry and dwarf fruit trees will not be happy in full sun, west-facing locations and gusty winds. Likewise, robust, tough trees including Kentucky coffee tree, Hackberry and Chinkapin oak can handle tougher environmental conditions once well established.

Tree planting

• Always call 8-1-1 before digging to locate underground utility lines. This is a free service.

• Keep the tree moist, shaded and in a protected site before planting. Be gentle when handling the new tree.

• The main goal is to help the tree start rooting right after planting. If the root system is not planted correctly, then the tree will not establish well and flourish.

• An incorrectly planted tree looks like a telephone pole in the ground.

• Planting too deeply has become a very common practice and needs to stop. Deeply planted trees will decline, often slowly, and many will die.

• The root flare, also called the root collar, is located where the trunk transitions from the bark into the visible roots. These roots should grow outward from the base of the tree slightly above soil level. This creates a collar or “flare” of roots that should always be exposed and not covered with soil, mulch or any materials like weed cloth.

• Use the root flare location at the base of the tree as a guide for correct planting depth. The root flare may not be visible in the container from the nursery. If this is the case remove soil until the flare is found before planting.

• The root ball of the tree needs to be planted slightly above the ground level. The root flare must be visible, a good 1 inch above the final grade or soil line after planting.

• For both container and balled-and-burlapped grown trees dig a wide, shallow, bowl-shaped hole. The hole should be three times as wide as the root ball. The planting hole depth should be only as deep as the root ball height.

• Hold onto the backfill soil, you will use that to fill in the hole after planting.

• Place the root ball on undisturbed, firm soil (not fluffed up, the root ball will sink down too much). Remove as much of the burlap or plastic wrapping, ropes and wire as possible. If the burlap is keeping the root ball together, then make several slits and peel it back to the ground. Remove as much of the wire as possible.

• A container-grown tree will need a good root ball haircut before being planted. Once removed from the container, take a saw and slice off an inch of the root system, soil and all, on all sides of the root ball. (See the Tree Planting 101 link for detail and photos.)

• There is no need to amend the planting hole with the back-fill soil unless it is very poor and overly clayey or sandy. Only add up to 5% amendment mixed well with the native soil. Correct planting depth and width is more important to proper root establishment than amending the planting hole.

• Fill in the planting hole. When three-quarters filled with soil slowly add water, and then finish filling the hole with soil. Make sure the top of the soil slopes away from the trunk. Water it once again.

• Staking is generally not needed unless the site is windy, or the new tree might get disturbed by passersby or it’s planted in a busy yard. Use flat grommeted straps, never use wire, rope or hose pieces.

• Wood chip mulch is recommended to a depth of 2-4 inches; keep it away from the trunk. The mulch ring should be three times the size of the root ball and increased over time as the tree grows. Turf grass competes with tree roots and in time the tree usually wins, and turf suffers.

• Recently planted trees and shrubs will need frequent, light watering; the root ball can dry out in just a few days in hot weather. No need to fertilize at planting time.

• Paper wrap the trunk area on new trees around Halloween and remove at Easter. This will provide protection from sunscald and extreme temperature swings which can kill active tissue. Look for tree wrap in area garden centers.

Your tree, long term

If the tree is planted in a mulched area (not lawn), then some type of a drip system is advisable. Too often with new trees drip lines are minimal, only routed to the root ball on a young tree. As the tree matures, add drip lines further away from the root ball to satisfy the expanding roots’ increased need for water.

Whether you plant the tree yourself or have it done by a professional, partner with a reputable tree care company that can advise on tree health including necessary structural pruning as the tree grows. They will be your first call after damaging storms and any other concerns. Think of your tree professional like your family doctor who will be there for annual check-ups and the occasional broken arm.

Colorado tree care resources

  • Recommended Trees for Front Range Communities
  • Tree Selection: Right Plant, Right Place
  • Tree Planting Steps
  • Tree Planting 101
  • Free and Low-Cost Denver Digs Trees
  • Find a Certified Arborist
  • Rollinger 50-Year Survey Study of Denver Trees

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