Lawns, Plants, & Trees

Mulching lawn mowers save work and make healthier green lawns.

Beautiful, sustainable, easily-maintained landscapes start with healthy soil, and the right plant in the right place. See the Resources for more on lawn, plant and tree selection, installation and maintenance.

Sustainable lawn care

These practices work with nature to create cost-efficient, healthy lawns that need less water and chemical inputs. Northwest landscape professionals and scientists have developed and proven these methods on a wide variety of sites. Their recommendations include:

• Realistic expectations: Northwest lawns are a meadow-green color, can have a few weeds, and are thick, wear resistant and healthy.
• Assess sites to plan practices and soil improvement.
• Choose site-adapted grasses, and maintenance practices.
• Mow regularly: 2-3” on rye/fescue, 1-1½” on bent grass).
• Mulch mow – leave clippings to improve soil, grass health, drought resistance, and reduce fertilizer needs.
• Test soil every 2-3 years, and correct any deficiencies.
• Fertilize only when needed, with natural organic or slow-release fertilizers – fall is the key time to fertilize.
• Irrigate deeply but less frequently to build deeper roots.
• Adjust timers for season and weather. Or let low-traffic turf go brown, watering only once each dry month.
• Renovate poor lawn areas with aeration, over-seeding, and compost topdressing. Or fix soil and replant.
• Use IPM: integrated pest, weed & disease management.

Plant selection and care

Key practices for creating sustainable landscapes include:

• Start with the soil: build healthy soil with compost & mulch.
• Choose the right plants for your site – plants that will thrive in the sun, soil, moisture, and use conditions, and grow well together.
• Select plants for low maintenance needs: low water and fertilizer needs after establishment, pest resistance, and minimal pruning.
• Use native plant communities where they fit the site conditions and design. Protect or restore natural “buffer” areas near waterways, slopes, and other sensitive areas.
• Group plants by their needs: soil, shade/sun, and water (“hydrozones”).
• Establishment (the first 2-3 years) is critical: water through the summers. Plant in fall or spring to reduce stress. Mulch annually until the canopy closes. Pull weeds before they seed. Replace failing plants with more site-appropriate and resistant species.
• After establishment, reduce watering. Use smart irrigation controllers and practices to conserve water and grow healthier, more drought-resistant landscapes.
• Compost and mulch will feed the soil to provide most needs. Base any fertilizer use on soil tests and plant symptoms, and look for “natural organic” or “slow release” fertilizers.
• Monitor plant health regularly, and use integrated pest management (IPM) to maintain health.
• Develop a Landscape Maintenance Plan to guide long term care, and educate managers and staff.

Tree protection, installation and care

Trees provide many benefits in urban environments, including storm water management, air purification, climate moderation, habitat, and making our city livable and beautiful.

• Fit trees into your site: generally plant conifers to north of buildings to provide shelter, and deciduous trees to south for summer shading and winter light.
• Plan vertically in layers, like the forest: ground cover, understory shrubs, and trees.
• Select trees based on mature size, to minimize pruning, provide adequate rooting space, and to avoid conflicts with overhead utility lines. Select small trees under 25 feet at maturity in locations under overhead power lines. Select low shrubs and limb-able trees where sightlines are important, such as street intersections. Provide adequate soil volume for the mature tree’s roots, or select smaller species where soil volume is limited. Where space allows, select large trees that provide the most the most benefits to people and the environment, including reducing stormwater runoff and higher quality habitat for wildlife. For help with tree selection, check out Trees for Neighborhoods.
• Select trees with multiple benefits: natives for habitat, fruit trees for food. Many non-native trees can be excellent urban trees because of their ability to thrive in disturbed urban soils.
• Plant trees right: Spread out the roots and prune any circling or girdling roots. Expose the root flare (where the first major roots extend from the trunk) and plant the tree with the root flare about 1 inch higher than the soil height. Learn more about planting at Trees for Seattle.
• Protect existing trees during construction by fencing off the root zone area. If temporary vehicle passage is necessary, use metal plates, thick plywood, or 6 inches of coarse wood chips or rock to spread tire loads. Learn more about tree protection at Trees for Seattle.
• Protect trees from root zone compaction, lawn herbicide application, and improper pruning. Monitor tree health annually in fall and spring. Consult a certified arborist if you see signs of decline.
• Pruning trees properly is essential to build strong structure and form for a healthy mature tree. Improper pruning techniques such as topping, seriously damage a tree. Consider hiring a certified arborist for the job. If you’re planning to prune a street tree branch over 3’’, you must obtain a tree pruning permit from SDOT.