Key takeaways for planting trees
DO 
- Call 811 before you dig
- Dig a wide hole
- Find the trunk flare
- Remove circling roots
- Water immediately after planting
- Apply mulch
DO NOT 
- Plant too deep
- Dig too narrow
- Bury the container or burlap bag
- Place mulch against the trunk
- Forget to water regularly
If you’re planning to plant a tree this fall, now is the time to get started; there are only a few weeks left in Colorado’s prime planting season.
Early fall, from Sept. 1 to about Oct. 15, is an ideal time to plant trees in Colorado. The soil is still warm enough for roots to establish before winter, while cooler, shorter days allow trees to put more energy into root growth rather than producing new leaves.
Tree survival and growth depend on several factors.
Follow these steps to give your new tree the best chance of success.
1. Call 811 before you dig.
Tree planting is considered excavation, so call 811 or visit colorado811.org before digging! This free and easy-to-use service connects you with utility providers who can identify buried utility lines.
2. Find the trunk flare.
Don’t start digging your planting hole until you know where the trunk flare is. When planting a container-grown tree, you will likely need to carefully remove some soil from the top of the root ball to find the flare. You may encounter small, thin roots along the way, but don’t mistake these for the roots you’re looking for! Look for the larger structural roots that flare outward from the trunk.
Trees are often planted too deeply, which can limit the oxygen available to the roots. This slows growth and can eventually kill the tree. A newly planted tree should not look like a telephone pole; the trunk should widen at the base to create a shape like a skirt.
3. Dig the right-size hole.
First, measure the distance from the bottom of the root ball to the base of the trunk flare. This tells you how deep you should dig.
Then measure the diameter of the root ball. Dig a saucer-shaped hole as deep as the root ball measurement and 2 to 3 times wider than the root ball. Loosening the surrounding soil gives new roots room to grow.
4. Remove problematic roots.
Lay the tree on its side and remove it from its container, including burlap or biodegradable containers.
Any roots that circle the root ball or grow across the trunk rather than away from the trunk should be removed.
To improve the future health of your new tree, place the tree in the planting hole and shave off any circling roots along the outside edge of the root ball. These are roots that have grown to the perimeter of the container and have begun to circle the root ball.
Shave about 1 to 1½ inches of soil from the outside of the root ball, shaping it into a roughly square shape. Shaving the root ball is recommended because it encourages fresh roots to grow outward into the surrounding soil, even if no circling roots are visible.
If large woody roots are circling the root ball or tree trunk, use hand pruners to cut them. Make sure the cut faces out toward the planting hole, so new roots grow away from the trunk.
5. Backfill with the soil you dug out.
Don’t fill the hole with soil from somewhere else, instead, use the soil you removed when digging the hole. If that’s not possible, use soil from near the planting site. Potting mix and other bagged soils with a different texture from the on-site soil can create issues with water movement and root growth.
Firmly pack a ring of soil around the base of the root ball to help stabilize the tree, then gently tamp the remaining soil around the root ball. Water as you backfill to help eliminate large air pockets.
Don’t stomp or tightly compact the soil. Roots need small air spaces to survive.
6. Add mulch – but keep it off the trunk.
Apply mulch 3 to 4 inches deep around the tree to help retain moisture and to create a barrier between any surrounding grass and the tree.
Keep mulch away from the trunk and don’t pile it over the root ball. Direct contact between mulch and the tree bark can damage the bark.
7. Keep watering.
Proper watering is critical to the survival of newly planted trees. How much water a tree needs depends on the species, soil type and drainage. The larger a newly planted tree is, the more water it will need.
And don’t forget to water your trees throughout the winter.
8. Watch your tree grow
How long before you see a newly planted tree grow depends in part on how quickly its roots establish.
One way to estimate how long that will take is by measuring the tree’s caliper. The caliper is how wide the trunk is at 6 inches above the top of the root ball. As a general rule, expect about one year of root establishment for each inch of caliper before significant canopy growth begins. So, a tree with a 2-inch caliper may take about two growing seasons to establish its roots before you start to see growth above ground.
“Bigger isn’t always better when it comes to buying trees at nurseries because larger trees can take longer to establish after planting. I prefer trees that are 1.5 to 2 inches in caliper, which is usually a 15-gallon tree, because it takes less time for that tree to grow into the vision you have for your landscape,” said Kamie Long, an urban and community forestry program specialist with Colorado State Forest Service.
More information on tree selection and planting
Information for this article is derived from Planting for Success: Tree Series Part 2. Watch the video for full details, including guidance on staking, tree guards, fertilizer, pruning at planting and more.
- For step-by-step instructions, see our guide for planting a container-grown tree.
- Additional tips for growing great trees can be found in the CSFS planting guide.
- If you need help choosing a tree, check out our guide on selecting, planting, and caring for trees or CSU Extention’s landscaping resources page.