Denver and the Front Range community has a semi-arid climate which causes dry winter conditions with very cold temperatures at times and hot, low humidity summer with intense sunshine. There would actually be very few trees on the eastern plains if not for development and irrigation. Mature trees do not need to be watered during spring or fall as these are the wettest months of the season or if the trees are irrigated. Drought stress affects the trees to some degree most summers and can be accelerated by high winds, reflective heat or residual heat in an urban setting. During the winter, trees will need supplemental water to withstand cold, dry, windy conditions which allows for transpiration. Newly planted trees and shrubs will establish most quickly with frequent, light watering.
Winter tree and shrub watering is done to ensure that your trees will remain healthy during this stressful time of year. It will help to prevent transpiration, tip burn, frost/freeze cracks and help branches remain supple in the event of a heavy snow. Transpiration is the evaporation of water from the plant through the leaves or needles and is accelerated under windy, dry conditions. This will in turn make the plant more susceptible to tip burn, trunk cracks and storm damage. During extended periods of time without snow cover, the root system can also become stressed due to soil evaporation. Trees in an urban environment may uptake added salts from ice melt or magnesium chloride and become burned. Plants with salt burn will benefit from the water flushing excessive salt from the soil. In most years, under normal conditions, 1-2 waterings should be sufficient to help protect against winter damage. Winter watering should not be done when the ground is frozen or if the air temperature is below freezing.
Summer tree and shrub watering will be necessary for many non-irrigated plants. The dry climate and extreme sunshine can cause drought stress and tip burn can appear on leaves and needles from the sun, heat reflected from buildings or rocks, or from radiant heat in an urban setting. Deciduous plants are prone to leaf scorch with browning along the edges or between the veins while evergreen trees and shrubs can have yellow, red or purple needles with brown tips which may move down the twig as the plant becomes drier. Drought stress may not kill the tree outright but continued drought with no supplemental water might. Once stressed the plants are more readily targeted by diseases and insects.
Winter and summer watering guideline:
Water deeply and slowly to a depth of 12” which is the critical zone for feeder root uptake.
Apply 2-10 gallons of water for each diameter inch of the tree. For instance, a 5” diameter tree would require 10-50 gallons each time it is watered. Deciduous trees should be watered from the drip line in and evergreen roots should be watered 3-5’ away from the end of the lower branches inwards towards the trunk.
Mulching of plants will also help them to maintain soil moisture though it should not be more than 4” deep so that it does not interfere with gas exchange.
Watering newly planted trees and shrubs is vital to the plants overall health. A new root ball can become dried out in just a matter of days if it is not being watered and will need added water even when drought conditions are not present. New root balls should be watered very, very slowly so that the soil does not separate from the roots. Extend the watering at least 6” past the root ball as this will encourage new growth.