Planting a tree puts us in touch with one of the most essential parts of a tree that is often overlooked—the roots. When a seed germinates, the first part to develop is the root. The seed has stored nutrients, but if the plant is to live, it must immediately make a relationship with the nourishment of the earth. Then it can make the sprout that pushes into the sunlight to start photosynthesizing. So the first matter of importance in planting a tree is to honor its roots—their condition, their future environment and their nourishment.

But before we dig a hole, we should take into account another matter of importance, namely the elements of size and time, so the right location and choice of tree are essential to tree planting. First determine if you want a shade tree or an ornamental or fruit tree. A shade tree will dominate the landscape. It will cool the house in the summer and provide a shady refuge outdoors. It will also cost more to be pruned and will limit the sun-loving plants that will grow near it. If you do want to plant a shade tree, plant it on the south side or the west side of the house for the greatest value. The late afternoon sun in Colorado is very intense coming through the west windows late in the day. Remember: most rock garden plants, many shrubs and flowering perennials, natives and xeriscape plants need at least 6 hours of direct sun.

An ornamental tree is one that is usually 15’-30’ tall and wide and that flopwers or has ornamental fruits, fall color, attractive leaves or bark. These should also be sited for best effect. They often branch lower than a shade tree and so can provide screening. But if 8’-10’ is enough to provide a screen, it might be better to plant a big shrub. If the tree is evergreen, be careful not to plant it where it will block our valuable winter sun to the  house or where it will shade a sidewalk or entry that will be icy in the winter. Don’t plant a tree under a power line or too close to the house or the sidewalk. Look around the neighborhood to see successful spacings of trees to structures.

Now that we know where to dig the hole, let’s consider how to dig the hole. For this article, I am assuming that we are planting a tree that is in a container. Most balled and burlap trees are too heavy for a homeowner, and I will mention B&B later.

The hole should be the same depth as it is in the pot and a minimum of twice the diameter of the pot and three times the diameter is better. A tree in a 5 gallon pot will require approximately a12” deep hole, a 7 or 10 gallon tree, a few inches deeper. Most tree roots live in the top 8”-12” with some bracing roots going deeper. That is because tree roots need oxygen and the nourishment that is more available in the top of the soil. When digging the hole, I take the top 6” and put it on one side of the hole and put the lower 6” on the other side. Some people like to slope the side of the hole and maybe that is helpful.

Next we must determine what to add to the soil in which we will be planting our tree. It has become popular lately to instruct us to not use amendments, but to plant in the soil just as it is. It is claimed that if we put compost in the backfill that the tree will grow confined and confused as if in a pot or that amendments are not needed. And if I were planting a tree in Iowa soil, I might agree, but I always plant with 1/3 compost and 2/3 original soil. Certainly if we use more than 50% compost we could have problems. And if we plant in unamended soil, most trees will still grow. But these are my reasons for amending: Almost all Colorado soils are low in organic matter and nitrogen. Compost holds water to help get a tree established when it has few roots. Compost opens the structure of the soil allowing rain to penetrate to the roots and allowing air to the roots. It also allows the new hair roots to more easily push through the soil. And compost provides food for the soil life to prosper. These beneficial fungi, bacteria, earthworms etc bring water and nutrients, dissolve minerals and in many ways support the health of the tree.

Besides adding compost we can add microorganisms directly. There is always life in the soil, but we have found by experience that adding some extra at planting, supports a more rapid root development which helps a tree establish faster and to grow more successfully. The first month of a tree’s life after planting is the most critical to its success. We can use a powdered mycorrhizae, wetting the tree roots and dusting on a small amount. We can use a water soluble form and directly apply it to the roots with a watering can, or we can apply a microbe-rich compost tea or even a worm casting tea to the roots before planting. Adding mycorrhizae is most important in new developments where the soil may be trucked-in subsoil with little soil life.

Some trees like pear, apple, crabapple, aspen or birch need ample air to their roots; in poorly drained soils these trees are susceptible to fireblight, fungal diseases or root rot. Especially if the soil is a dense clay or is in a low spot that collects water, it helps to mix 10%-20% Expanded Shale into the backfill. This locally mined shale is fired in a kiln which makes it porous so that it holds both water and air and does not break down over time, like compost does. This makes Expanded Shale a true “clay-buster”. In addition, it may be helpful to add a little organic fertilizer to the backfill. Since our soils are often low in nitrogen, an organic fertilizer that is 3%-8% nitrogen can be helpful. The old warning not to fertilize when planting is only valid for chemical fertilizers that are water soluble and force top growth when the roots need to establish. Organic fertilizers are slow-release, and a half cup to a cup will provide nutrients both for the tree and for the beneficial microorganisms. All these amendments should be added to the top layer of soil taken from your hole.

So now you can take the tree out of the pot. Lift it by the trunk (maybe with a helper) and tap on the edge of the pot all around until the pot falls off. Then set the tree on the ground and tease the roots out of their confined form so they are not circling but are ready to move into the surrounding soil. If the tree has been in the container too long and you can’t pull the roots out of the circling shape, you may have to cut a few roots to open them up. Tip the tree on its side and loosen or cut the roots on the bottom. When a tree grows from a seed, it makes an open root system. So help your new tree with that in mind.

If the ground is dry, put water in the hole before planting, and let it sink in. Then sit your tree in its big hole. The depth is critical. There have been many problems with people planting too deep. This will suffocate the roots and put wet soil against the trunk bark which is not adapted to wet and can rot. This is a common problem with Balled and Burlap trees that are put into containers and “topped-off” with soil. The over-reaction to this is planting too high. This is also a problem because the roots are not designed to be in the sunlight and air, and the tree will dry out out, even if it is drought-resistant. When I interviewed the late, great tree scientist Alex Shigo in 2000 for the Colorado Gardener, he said, “Why not plant a tree at the correct depth? Where the trunk flares should be the ground level.” You can place a board across the hole level with the ground to check where the soil level will be on the trunk. Then if it is too high, dig a little deeper and if it is too low, lift out the tree and add a little soil. If you have to add a lot, tamp the soil so the tree does not settle too deep. Now wet the roots with mycorrhizae.

Then add the amended backfill soil 3”-4” at a time firming a little with your hands, adding water and then some more soil until it is filled to the proper depth. Now take the subsoil on the other side of the hole and make a little berm around the tree, the same diameter as the hole and fill that with water. If you have planted the tree in a lawn, you can place a tree ring 1” thick and 2’-3’ in diameter around the tree. They are made of recycled rubber that lets water through but keeps weeds and grass from growing near the trunk. This is very important to keep mowers and weed trimmers from damaging the young tree trunks. If not in a lawn, the berm-well can be filled with 2” of wood chip mulch. Be sure this mulch is at least 2” from the trunk, because wet mulch can rot the bark.

It can be very helpful to use a tree wrap to prevent sun scald, to prevent rabbits from eating the bark and deer from shredding the bark with their antlers in the velvet stage. The thin bark of a young tree can be damaged by our stronger winter sun, especially if the tree was grown in Oregon. In the old days when a tree was dug, the south side of the trunk was marked and then oriented in the same direction when it was planted. Paper tree wraps can hold moisture against the bark, and are only supposed to be left on through the winter. I like the plastic spiral tree wraps that shade and shield the trunk from animals, but allow air to circulate underneath.

A potted tree rarely needs staking, because the top is not that big and it is better for strong trunk development for it to flex in the wind. If there are broken branches or dead branches or stubs, these can be removed, but a young tree benefits from every leaf that photosynthesizes. If the tree is very tall and whispy, then tip no more than 10% of its height. Otherwise, leave the pruning for a later year.

A company selling Balled and Burlap (B&B) trees has advertised, “Plant a tree, not a stick”, and certainly a new containerized tree can be very small, but it has a developed root system and will begin growing immediately. Many B&B trees are successful, but when they are dug in the field, 50%-90% of their roots are left in the ground, so they are naturally stressed and can take one or two years to start growing.

Alex Shigo instructed us to “Touch Trees”. If we touch our tree to be planted with care and with the knowledge that it can live long and will often benefit others beyond our own lifetime, then we will see that it is well-planted.



Trees do a lot for us humans, so we shouldn’t forget to give them some support. When I look at the treeless ten acre lot next to our nursery, or when I see an old photo of the CU campus with bare land around Old Main, I remember why we can’t take trees for granted in Colorado. Trees really have it hard here, but there are things we can do to help them survive and thrive.

To begin, we must choose tree varieties that like Colorado conditions. The CSU website has a very valuable downloadable resource to help us, the Front Range Tree Recommendation List. 250 trees were evaluated by local experts and the trees are rated A thru D for their success. Just because you see stunning photos or have fond memories of Pin Oaks, Red Maples and Bradford Pears doesn’t mean they will thrive in our alkaline soils, violent temperture swings and the worst fireblight in the country. For example: never plant an apple or pear that is not resistant to fireblight. A Radiant Crab is rated “A”, a Royalty Crab “D” because of fireblight. And our alkaline soils make certain nutrients, like iron, less available, resulting in weakened trees of some varieties.

And it is important where you buy a tree. Trees are not well cared for in Big Box stores and a stressed tree is a poor investment. Some Balled-and Burlap trees come from Oregon or other dissimilar environments. B&B trees do better if they are locally grown. They also do better if they are not too big. People want to start with a big tree, but the bigger the trunk diameter, the more roots that are left in the ground when they are dug. A tree with a 2” trunk diameter will need less water to establish and will be less stressed than a 4” diameter tree, and will start growing faster.

With our average annual rainfall between 12” and 20”, we have to water most trees, and lawn irrigation systems are not designed for trees. Most trees want deeper and less frequent waterings than bluegrass lawns. In fact most trees would be a lot happier outside a lawn. Jack Phillips, principal of New Tree School, has said “Trees did not evolve in landscapes dominated by lawn…Progressive tree care requires a movement away from green sterility and toward a wilderness in soil.”

What Jack means is that not only does grass drink a tree’s water and starve it for oxygen, chemical lawn care starves it for organic matter and kills off the soil life that are a tree’s allies. Trees need less water in spring when we have precipitation and twice the watering in July when it is so hot and dry. Remember: soggy soils have little space for air, and trees need oxygen to their roots as much as they need water.

Because of our dry autumns, sunny winters and winter warm spells it is very helpful to trees to winter-water, especially evergreen trees and trees planted in the current year. Water early on a sunny day to give time for the water to soak in before night-time freezing. Water long enough to penetrate 6”-8”. No need to water if the ground is frozen. A sprinkler works better than a deep-root needle. Remember: Colorado is in a semi-arid region, we are a mile closer to the sun and we lack the winter cloud cover of the regions where many of us grew up, and where most of our trees originated.

Our soils are not the rich glacier deposits of the Midwest. Clay is okay, but it needs more than water to grow strong trees. There are exceptions: native oaks, Russian Hawthorn, Boxelder. But unamended Colorado soils are all deficient in organic matter and nitrogen, from a tree’s point of view. There are those that disagree with me, but I will stand my ground, based on 35 years in the tree care business.

I do not believe in using chemical fertilizers which are made from natural gas, lack micronutrients and are water soluble, pushing fast growth that is soft and susceptible to fungal diseases and sucking insects. I do believe in planting a tree with 30% compost and a little organic fertilizer. And I think periodic feeding with an organic fertilizer and minerals is good, especially if you also are giving the tree some mycorrhizae and mulching over the root zone. I favor this approach because I believe it is necessary to make up for the lack of natural pile-up of leaves and branches that feed the soil on the forest floor. Yes, there are already mycorrhizae in our poor soils, but experience shows that trees establish faster and have fewer disease problems and need less water when humans give them a good mycorrhizae supplement or compost tea. And yes, trees will grow without fertilizer, but not only will they grow faster, but trees with good nutrition will be stronger and more able to cope with Colorado’s harsh environmental conditions. The two best times to fertilize are early spring and early fall and the best time is early fall, because that is when trees are storing nutrients in their roots and stems. This is where the energy will come from if they have to make a new set of leaves after a late spring freeze or to ward off an insect or disease.

According to research done by Ralph Zentz, a Ft. Collins city forester, 70%-90% of all tree problems are abiotic. That means few tree problems are caused by insects and diseases; most are caused by environmental and cultural conditions. This is good news since it means,  we can generally support our trees without spraying anything or having to pay to have something (especially something toxic) sprayed on our trees. So choose a tree that likes Colorado, plant it in the sun or part shade if it prefers, water it deeply and infrequently and once a month in the winter, prune it correctly, and give it organic nutrition so that its soil allies will prosper. Then it will have the vitality to breathe carbon from the atmosphere and build a structure that stands the wind and snow, and provides shade, fruit, beauty and habitat.