Winter Care of Young Trees in Denver

In the fall and winter, trees drop their leaves and become dormant as they prepare for colder temperatures. Newly planted trees benefit tremendously from winter young tree care. Believe it or not newly planted trees experience the greatest growth in their root system during this time. According to the Denver Post, trees recently planted are particularly vulnerable because of Denver’s dry winters because lack of moisture can dry out and kill these roots. Not watering throughout the winter is the largest contributing factor to the mortality of newly planted trees.

The following fall and winter watering tips should be used for three years after planting a tree. It takes trees about three years to develop their root systems.

Cool Month Watering Routine

• Fall – Homeowners should tart watering saplings in September and October before the first hard freeze. Slowly trickle water under a tree’s drip line for several hours. Check the ground every two weeks. If the ground is rock hard and dry it is time to water.

• Winter – It is not unusual in Denver to get a warm day in the dead of winter. Take advantage when temperatures are in the 40s to water newly planted trees by allowing the water to soak in before the water freezes at night.

Additional Tips

• Wrap the Trunk – Denver winters with their warm days trigger bark cell growth and movement of nutrients in a tree’s cambium. When temperatures suddenly drop, this new growth freezes causing sun scald and frost cracks. Sunscald is also called Southwest injury because the damage is usually on the southwest side of trees. In Denver, the trunks of young trees, especially thin-barked trees like Honeylocust, Maple, and Linden, need to be wrapped to prevent these conditions.  Apply commercial-grade tree wrapping tape in late fall before the first hard freeze. Homeowners be sure to take the wrap off in the spring usually around Easter.

• Mulch the Base – Mulching around trees reduces soil evaporation, improves water absorption, and diminishes
  soil temperature fluctuations. Apply two to four inches around the base of each tree but do not allow the mulch to touch the trunk. Allowing the mulch to touch the tree over time can cause rot and stem girdling roots harming the tree.

• Fertilization – Young trees benefit from fall fertilization to winter root system growth. Tree root systems use the nutrients to grow and store food for the next growing season supporting more robust leaf and flower bud growth.  Ross Tree recommends using fertilizers low in Nitrogen for fall feeding.

Pruning Young Trees in the Winter

Structural pruning works best on young trees because their branch structure is not fully developed and easily trained. Yard trees are fundamentally different from forest trees because, in a forest setting, trees compete with their neighbors for light. Forest trees form slender tall trunks with fewer and smaller lateral branches in their lower canopy. On the other hand, yard trees with abundant light grow wide with multiple competing leaders and many lateral branches. Gangly trees are more susceptible to mechanical breakage from wind and snow storms. Heavy, thick, crowns keep light out and moist in making them vulnerable to disease and fungi. The main goal of structural pruning is to form a single dominant leader with later branches strongly attached to parent branches.

It is a common misconception that late fall and winter pruning is not good for trees. The reality is that trees set their flower and leave buds in late summer making winter a great time for pruning. Trees generally have plenty of stored energy from the previous growing season to heal wounds properly. After the leaves drop, it is easier to evaluate the tree’s branch structure and make better pruning decisions. Minor pruning on branches less than two inches in diameter can be done anytime.

Rules of Thumb

• Pruning Dose – It takes about three years for the root system of newly planted saplings to get established. During those three years, pruning should be limited to dead and broken branches and correcting major structural defects. The American National Standards Institute (ANSI) standards state that 25% of a healthy tree’s foliage is the maximum that can be removed each year. Property owners should remove as little foliage as possible while still meeting their pruning objectives. Trees under persistent drought stress should not be pruned.
• Pruning Cut Size – Pruning cuts two inches or less in diameter heal faster. Pruning cuts larger than four inches should be made when there is no choice because large cuts take longer to heal and sometimes lead to decay.

• Crown Density – A healthy tree has a least 60 percent of its height as a canopy with 40 percent as the trunk.

 

Strategies for Structural Pruning of Young Shade Trees