How Trees Work to Manage Rain and Stormwater

Photo shows a house with a tree in the side yard.
Trees are a readily available, natural way to manage the rain on your property. Trees are easy to plant, low-cost, and most property owners can do the work themselves. Learn about the types of trees best suited for your property before planting.
On this page

How Trees Work to Manage Rain

Trees capture and hold rainwater on their leaves and branches. They can decrease the total extra water running over the ground by 35 percent or more for small storms. The average street tree in Portland captures almost 600 gallons of rain each year.

Trees improve water quality in many ways. First, trees help some rainwater to soak into the ground, where it is cooled and filtered naturally.  Second, by reducing the amount of water flowing over the ground, trees reduce pollution picked up by the water and carried to streams.

Trees also hold soils in place, which is especially important along stream banks, and they provide shade. Trees shade buildings and reduce pavement heat, which in turn lowers the temperature of any water flowing off the street and into a river or stream. Trees planted near creeks and streams provide shade that helps to keep the water cool for fish and insects.  

 Trees provide many benefits whether planted along a stream, along your street, or in your yard.

Summary of Site and Design Requirements and Tips for Trees

Keep in mind the following tips when choosing and planting trees to manage rain on your property:

  • Learn about the difference between “street trees” and “private trees.”
  • Locate trees where their canopy can cover the “impervious” areas on your property. Impervious areas are roofs, sidewalks, patios, and driveways, where water cannot soak in. This way, their canopy catches the rain before it hits the ground.  
  • Choose trees suitable for your property’s soil type, available sunlight, and space.
  • Consider planting trees native to this region. Check out the City’s Native Tree List.
  • Do not select a tree listed on the City’s Nuisance Tree List.  
  • Learn how to properly plant and care for a tree so it survives and thrives. Find information on this site or at Friends of Trees website under how to plant and care for your tree.

When to Call a Professional

Locate utilities before digging to plant a tree. Call 811 or 503-246-6699 (local) or 1-800-332-2344 (toll free) to locate utility lines underground on your property.  

Most property owners can plant trees without help. Read the "How to Plant Properly" guide.

Professional contractors or landscapers can help you select and plant trees if you need help.

Consult a certified arborist for tree care you cannot safely perform on your own.

Costs and Permits

Costs vary with the type and size of the tree, but the general price range per tree is $50-$200, not including planting. Local nonprofit groups often supply free or low-cost trees. Check out the CIty's Tree Planting Programs for free or subsidized trees.

Private Property Trees. No permits are required for planting trees on private property. (However, a permit may be required to remove a tree on private property.) If you plant your tree between September 1 and April 30, you could qualify for a Treebate and receive a one-time credit on your water, sewer, stormwater bill. Learn more or apply at About Treebate.  

Street Trees are regulated by Portland Parks Urban Forestry. Planting, removing, pruning and other activities regarding trees in the public right-of-way require a tree permit. Find more information about tree permits from Portland Parks Urban Forestry or call 503-823-TREE (8733).

If your property has an environmental overlay zone, or E-Zone, there are E-Zone regulations regarding trees.  

Many development projects have tree preservation and tree density requirements. Learn more about tree requirements reviewed as part of a building permit application.  

Maintenance Requirements

Newly planted trees need deep watering in the dry summer months (May to September) until they are established. Give newly planted trees at least 10 gallons of water each week, or when the soil is dry.

Other tree care tips for new trees:

  • Stake trees loosely for the first two years to protect them from tipping over. Always remove stakes and ties when they are no longer needed.
  • Apply a mulch ring to direct water to the tree’s roots, suppress weeds, and keep soil from drying out.
  • Protect the bark from damage.

Routine tree maintenance may include:

  • Raking and disposing of leaves and fallen branches from streets and sidewalks. Removing weeds.
  • Pruning out dead branches.
  • Pruning for good structure and clearance.
  • Mulching over the roots of the tree.  

Consult a certified arborist for tree care you cannot safely perform on your own.

Find more tree care tips and resources.

Stormwater Management Manual

Consult the City’s Stormwater Management Manual for complete details on tree credits during development and permitting. Consult Urban Forestry for complete information on all City tree regulations, permits, and information on how to safely site, plant, and maintain trees.  

Portland's Clean River Rewards Program

Residential and commercial property owners who install qualified stormwater management solutions may be eligible for discounts on the stormwater charges of their sewer, stormwater, and water bill through Clean River Rewards.  

Trees are eligible for Portland's Stormwater Discount Program. To count toward the discount, the trees must be on your private property. Street trees in the right-of-way or planting strip (often between the sidewalk and the curb) don't count toward the discount.

To be eligible for Clean River Rewards with trees as your stormwater management solution, a minimum of four trees on your property, each at least 15 feet tall, are needed to receive a credit. You may also be eligible if you have fewer than four trees, but they are large and have a canopy size of 200 square feet or more. Visit Clean River Rewards to learn more.

Plant a tree in your yard from September 1 through April 30, and you could be eligible for Treebate – a one-time credit on your sewer, stormwater, and water bill for the cost of the tree. Learn more at About Treebate.


Systems Development

Environmental Services
phone number503-823-7761Questions about sewer connections, stormwater management, and drainage reserves at the land use or building permit stage.

Environmental Services Tree Program

phone number503-823-2255For questions about Treebate and Environmental Services' tree planting opportunities for industrial, commercial, and multifamily properties.