Tree Care
Pruning
Tree pruning should not be undertaken lightly, it is an inherently invasive process which opens the tree up to decay. However it is often necessary to produce a tree which will remain the landscape for many decades or centuries.
Pruning should start with an analysis of the age, health and inherent growth pattern of the tree, followed by asking the questions, "What do I hope to accomplish by pruning my tree?".
If your answer is "I don't know." or "To keep the tree under control." or "Its due for a pruning" then you should seek the advice of a professional arborist. Many times the best intentions can lead to exactly the opposite of the intended goal and a trained arborist can guide you or prune the tree to accomplish your management objectives.
Remember, trees in the parking strip belong to all of us so a permit is required to prune these trees. Part of the Sustainability Initiatives Fund pays for maintenance of trees in the parking strip so please contact the Urban Forester if you believe a tree needs pruning. We are currently working to prune all trees under 10" in diameter on a 5 year cycle to ensure good structure, older trees are our next target. This program is evolving so please check back for updates.
With all this in mind please visit the this site for some excellent guidance on structural pruning of young trees.
Please visit Public Works website for rules on maintaining vision clearances near intersections and driveways.
Mulching
Much can be said about the benefits of mulching trees. Mulching provides insulation for tree roots and soil to moderate soil temperatures and reduce water loss through evaporation. In addition it reduces competitive weeds and turf near the tree.
Mulch comes in many forms from recycled rubber tires to unprocessed wood chips. If you are mulching a tree the greatest benefits can be obtained through the use of arborist's wood chips or a mix of bark and chips. This material provides a good source of nutrients as well as decomposing to improve soil microbial activity and soil aggregation (structure). When using wood chips make sure they do not come from a walnut tree as this wood contains chemicals which can retard tree growth or from a tree which has died from a soil transmissible disease such as Virticillium wilt.
Mulch should be applied as needed to maintain a 2-4" thick layer. It should be applied approximately 4" away from the tree out to the edge of the trees canopy. If mulching a group of trees the greatest benefits will be seen by mulching them as a group rather than in individual circles.
Mulch should never be placed against the trunk of a tree as it can promote the transmission of decay organisms from the mulch to the bark of the tree.
Do not use impervious plastic sheeting or fabric barriers under mulch as they limit the incorporation of organic matter into the soil and reduce available moisture.
Keep mulches 3' from buildings.
Watering
Young trees require supplemental watering to get established. In general established trees only require supplemental watering under a few select conditions such as extreme drought or when roots have been removed or damaged.
In fact some established trees such as our native Oregon white oak can experience significant root damage and decay from irrigation.
If you have existing trees and plan to install landscaping around them, consult an arborist who can help you select plant material compatible with your trees.
