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Urban Forestry
Arborist's Office
206-684-TREE (8733)
Street Tree Management Plan
Street Tree Planting Procedures
Permit Application to Plant a Tree
Tree Service Providers
Tree Pruning Guide
Tree Pruning / Removal Permit Request
Landscape Architecture
Seasonal Tree Care
Seasonal Information
After the Storm
Dutch Elm Diseased Trees
Tent Caterpillars
Prepare Your Trees for Winter
Utility/Tree Inspections
Heritage Tree Program
Seattle Tree Inventory
Urban Forestry Class and Resources

Proper watering, mulching, fertilizing and pruning of Street Trees

Newly planted street trees should be given extra care the first three years.

Attention to these several chores will help you to grow a tree that will be beautiful and healthy in the years to come.

A Calendar of Tree Maintenance


  • A good time to finish cleaning up old leaves around trees. They can carry disease and harbor overwintering insects. Check with a Master Gardener for information on spraying dormant oil on trees.

  • Pruning can be done this month.

  • Renew mulch around trees. Tree care companies can often be a great mulch source


  • Finish any chores left over from January before the first buds burst.

  • Apply fertilizer to early flowering trees so that the Spring rains can wash it into the ground.

  • Get a jump on the weeds. It's easier to pull them when they're little. Or you can wait for a sunny day and hoe them out and the sun will kill them.


  • Weed around trees and apply mulch. Competing sod should be removed from around trees. If lawn grows up to the base of trees, especially young ones, it will draw away needed nutrients and water.
    Find out more.

  • Keep string trimmers and lawn mowers away from the base of trees. Having mulch around the base of trees prevents injury to the bark often caused by equipment getting too close!

  • Examine your trees for signs of insect egg masses on the trunk or branches. Small groupings of yellow eggs that protrude from the bark are likely to ladybug beetle eggs. These insects are very beneficial as they eat aphids by the hundreds!

    Tent caterpillars are a common pest that lays their eggs on branches. They are quite visible to the naked eye and look and feel a bit like Styrofoam. You can save yourself a lot of trouble by scraping these off with your fingernail.


  • Arbor Month. Nominate a neighborhood landmark tree as a heritage Tree. Organize a tree care work party. Volunteer to help others plant and tend. Frequently April brings with it a dry spell. Be attuned to weather changes and water new plantings if rainfall is inadequate.


  • Summer pruning can be done now. Most trees need some attention while they are young in order to form a pleasing, clean, open structure and at the same time produce lots of flowers. Watch for watersprouts on any of the trees that have been heavily pruned the previous year. These should be removed as soon as they appear. Keep a diligent lookout for suckers from the rootstock of grafted or budded plants. Do not wait for them to grow large before removing them.

  • Planting of summer flowering bulbs can be done around trees, being careful not to disturb tree roots.

  • Continue watering of newly planted trees.

July and August

  • Summer months can be hot and dry. Make sure that newly planted trees receive adequate moisture so they can grow new, strong roots. Water at least once per week, making sure that soil is moistened to a depth of 18 – 24”. (That equals about 10 gallons of water for each diameter-inch of tree trunk - measured 6” above the ground)
  • Mature trees may need a good soak once a month, if they appear to be wilting, exhibiting fall color early in the year, or leaves are drying and/or falling.
  • Watering should be gradually tapered off in August so as to harden and ripen all growth before fall.


  • This is a good time to plant trees or start thinking about it. If trees were planted in the Spring then make sure they are growing straight. It only takes a tree a year to become firmly rooted so make any adjustments early.

  • Fall bulbs can be planted in the tree pits, being careful not to damage surface roots.

October and November

  • November is clean-up month in the garden. As the brilliance of the autumn leaves fade and start falling, your trees should be put to bed for the winter. Any foliage or growth that has been attacked by disease or that is likely to harbor the eggs of insect pests should be removed and gathered to send away in Clean Green. The healthy leaves make great mulch and compost.
  • This is a great time to weed and mulch trees.

  • November can bring storms with high winds. Young trees may need to be staked to prevent any damage.


  • Many of November's chores can be allowed to carry over into December in a mild season. If it snows remove snow from tree branches so the weight doesn't break them.

  • Now is a good time to prune dormant trees. Use sharp tools. Do not top trees!

  • Pruning cuts do not need any covering or sealer.

  • Prune Conifers.

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