Tending To Trees

By Linda Langelo

Parks and trees seem to be inseparable. We can shade ourselves from the hot summer sun beneath a centuries-old Cottonwood tree, listen to wind whisper through a Ponderosa Pine’s needle, notice the biodiversity that is housed in a welcoming Maple tree, and so much more. There is a great deal of work to maintain trees for visitors to enjoy an aesthetic and healthy park. When you think about it, trees have different age limits, as do people. Oaks can live between 300 and 400 years. Maple trees can live 200 or more years. Cottonwood trees live about 70 years, with some surviving 150 years.


Tree Longevity And Soil
How long a tree lives begins with its roots. The foundation of a healthy tree is matching the soil structure and pH with the tree that grows best in that soil. This begins with a soil test, which provides the pH, excess lime and nutrient levels, organic matter content, and more.

When a tree grows in the proper pH range, it seems to remain healthy and does well against disease and insects. However, soil structure and pH are not independent of one another. A pH between 5.5 and 6.5 can assist nutrient leaching, but above that it becomes a barrier to plants obtaining nutrients. Alkaline pH makes nutrients such as zinc and manganese unavailable, creates toxic elements, and changes how the soil structure behaves—particularly in clay soils. A soil test every few years will determine what the soil might need. There are many soils consisting of percentages of clay, sand, and loam. A clear picture of the percentage of these elements will offer an indication of how the soil will behave.

Well-drained soils are another characteristic that will provide healthy tree roots on trees such as catalpa, dogwood, and junipers. Tree roots require a balance of oxygen and water to their roots. Trees that need well-drained soils will suffer soil-borne diseases and other site-related issues over time if their root systems stay flooded. There are some trees that can handle extended water around the root system, such as Bald Cypress, Green Ash, Black Ash, Willows, River Birch, Swamp Tupelo, Sweetbay Magnolia, Atlantic White Cedar, Pin Oak, and Red Maple.

Right Plant, Right Place
Without understanding the soil make-up, there is little chance of getting the “right-plant, right-place” aspect correct. These include:

  • Hardiness zone
  • Height and width
  • Growth habit
  • Exposure
  • Disease and insect problems
  • Drought tolerance
  • Cladoptosis (process of a tree shedding smaller limbs in the fall).

The biggest hurdle to “right plant, right place” is obtaining accurate information on the tree(s) that are planned for a park or recreation area. Go to a local nursery, observe the tree(s), and ask qualified nursery staff questions. Travel to an arboretum and ask an arborist about disease and pruning.

After determining the hardiness zone, growth habit, height, width, the tree’s chances of surviving the winters, and whether it fits in the space designated, check the exposure. Will it do well facing prevailing winds? Will it do well in full sun? Does the tree prefer some shelter? Does it prefer a west exposure? Observe in the winter areas of the park or recreation area where the snow collects and where it melts quickly. In the summer, those areas are correspondingly cooler and warmer microclimates. Those trees may not need as much water. Western and southern exposures can cause sunscald on young trees during the winter. Keep a soil probe as part of a “tree tool kit.” Take a core sample from the feeder root area at the end of the dripline of a tree, the end of the tree’s limbs. This is actually the best place to water a tree.

Drought Tolerance
Trees need water in winter when there is no snow cover for that month. Watering is recommended for established trees every six weeks and for young trees every four weeks. A deep root feeder that can connect to a hose will deliver the water carefully placed at an eight- to 10-inch depth. No two deep root feeders are alike, so follow the instructions for the length of time in one area.

One formula for watering trees that is used by Colorado State University Extension employees is that for every inch of the tree’s diameter at knee height, the tree needs 10 inches of water. Is that every day or once a week? The amount of water will depend on the weather. Keep a record of daily weather. Maintaining a record season after season provides important data to assist with tree care and growth. Think of the watering as supplemental watering rather than regular watering. Water helps translocate proteins and nutrients while keeping the tree roots healthy. Water is part of every function of a tree. When a tree receives enough water, the tree’s cells are turgid, and this makes the tree limbs flexible. In the winter, this can account for less breakage of limbs.

Many trees can adapt to slight changes in conditions, especially if the trees are placed properly. It is the extreme conditions that need to be addressed. For example, in Northeast Colorado during October 2014, the temperature started at 75 degrees Fahrenheit and fell within a few hours to -9. This led to freeze damage. Freeze damage is not always readily seen. Behind the bark, the vascular structure may not repair itself over time, and a tree starts losing bark. Time will tell. If a dry spring follows a cold snap, give the tree some supplemental water.

Cladoptosis, Disease, And Insect Problems
Trees with good crotch angles (more than a 45-degree angle) are more sustainable. For example, a Bradford Pear is not suited to good crotch angles. The bark is included or pinched between the limbs. Select trees that do not exhibit a characteristic called Cladoptosis, mentioned earlier. These trees are ash, pines, poplars, willows, maples, walnuts, bald cypresses, oaks, and larches. These trees naturally shed their limbs in the fall as a self-pruning and/or drought response. When planted in the “right place,” they may not exhibit Cladoptosis.

A tree that sheds its leaves outside of the fall season may have a disease or insect problem. Any curling or discoloration of the leaves may indicate disease, or an insect or chemical problem. These aforementioned items are symptoms. A closer look will tell what the sign might be, such as an aphid curled inside the leaf.  Keep a record of these symptoms. Record the tree, time of year, duration, and document with photos.

Preventative Pruning
Preventative pruning is useful. Violent storms can do significant damage to healthy trees. Consult with an arborist every couple of years and assess the thinning of a park or recreation area’s trees. Thinning of large trees helps to lessen the density of the tree’s crown. In a violent storm, this can help mitigate the high-wind velocity by allowing the wind to pass through the branches. This can reduce mechanical stress on certain limbs, mitigating damage.  Pruned, healthier trees make for a safer park and a place to recreate. 

Consider this statement from Dr. Richard Leakey, a Kenyan paleoanthropologist and conservationist: “We make an immense mistake when we think of trees as solely an aesthetic member of a community. They cut pollution, they cool the air, they prevent erosion, they muffle sound, and they produce oxygen. Then, after all that, they look good.”

Linda Langelo is an Associate for the Colorado State University Extension, Golden Plains Area, Horticulture Program. Reach her at Linda.Langelo@colostate.edu.