Things you should know about watering trees
Trees provide many benefits to a neighborhood, besides increased property values, such as cooling in the summer, protection in the winter, storm water absorption and a great source of compost for our gardens. With approximately 16,000 street trees and 30,000 to 40,000 trees in parks and open spaces, there are just too many trees and too few resources to water all County trees. Therefore, staff focuses efforts on watering young trees with immature root systems. These are the most susceptible to drought conditions.
In the absence of significant rainfall, the Department of Parks, Recreation and Community Resources (DPRCR)is watering trees 5 days per week using two 1,200-gallon tank trucks and two 500-gallon portable tanks. Use of the two portable tanks, one of which is pulled by a trailer and the other mounted on a small dump truck, were added to the operation to increase watering efforts two years ago.
Since watering is critical to the survival of young trees and County resources are limited, staff asks residents to help water and care for trees that have been planted in the right-of-way in front of their houses. For the past several years staff has distributed letters to households shortly before trees are planted in front of their homes. The letter asks residents for their help and gives directions for watering young trees and replacement of mulch. It explains that, by watering the tree in front of their house, residents will permit DPRCR to devote more time and resources to trees in areas where access to water is more difficult, such as parks areas and street medians. The letter asks them to contact DPRCR so that trees can be put on the list for DPRCR to water if citizens are unable to help with watering the trees in front of their houses.
Enlisting the public's help with the care of young trees not only helps to stretch County resources and dedicate them to the care of trees in areas where access is more difficult, it also helps to get residents "invested" in this new addition to their neighborhood and forges a sense of ownership and volunteer partnership.
The current watering regime, in combination with assistance from many citizens watering newly-planted trees in front of their homes, has been sufficient to water trees that have been planted within the past two years. In addition, staff does water older trees (not on the "scheduled" watering list) when they note signs of wilting while watering younger trees in the area. If drought conditions become worse during the second half of the summer, additional staff time will be dedicated to increase watering efforts to 6 or 7 days per week in order to meet demands.
Trees planted within the past two years that are less than 6 feet tall need a minimum of 5 gallons for each watering. These trees should be watered at least twice a week starting in April and continuing through November. Rainfall should not be considered adequate unless it is 2" or greater.
The best time of day to water is early in the morning so that the amount of evaporation is minimized. Late in the evening is the second best time. The amount of water that comes through a hose varies for a variety of reasons such as hose size, length, size of the building's plumbing, water pressure, etc. However, you can still estimate that about two gallons of water flow through a typical garden hose per minute. This is roughly comparable to the amount of water that flows through the typical shower. Therefore, you should water newly planted trees for at least (3) three minutes with an unrestricted hose. Hoses with sprinklers may need to be run longer since sprinklers may restrict the amount of water that flows each minute.
Mulching not only helps a tree's appearance but helps a tree with water, too. Keep the tree mulched with compost (something you can create from your grass clippings and leaves), always creating a well around the trunk to allow for better water absorption. Don't place mulch in direct contact with the trunk of the tree.
Although watering trees is considered by most a wise use of water even in drought conditions, you may be asked to suspend watering of trees and lawns during these times. During drought conditions you will likely hear or see announcements in the news media regarding wise use of water and any voluntary or involuntary restrictions.
For more information about tree watering you may contact DPRCR at 703-228-7744 or extension service at 703-228-6400.