21.08.300 General landscaping standards.
A. General Site Preparation.
1. Compacted Soil. During site preparation soil must be loosened or uncompacted in landscape areas where necessary due to compaction. Soil must be uncompacted, at minimum, down to 24 inches below surface grade in any landscape buffer, street frontage, or parking lot landscaping areas. Depth of soil that is loosened or uncompacted may be less if recommended by the qualified landscape professional. Where necessary soil amendments may be added from a verified source.
2. Root Barriers. Trees planted within 10 feet of a public street, sidewalk, paved trail, or walkway must be a deep-rooted species and must be separated from hardscapes by a root barrier to prevent physical damage to public improvements.
3. Alternative Root Diversion. Alternative root diversion and barrier techniques will be considered if the applicant states the root diversion method on the landscape plans and provides a letter and any exhibits from the qualified landscape professional explaining how the method achieves the desired outcome.
B. General Plant Standards (Groundcover, Shrubs, and Trees).
1. Plant Selection. Plants must be appropriate for the Puget Sound lowland region. Permitted plants and trees are allowed as described below.
a. Prohibited Plants. Plants listed by the Washington State Noxious Weed Control Board in their Noxious Weed List or subsequent document, or commonly known as invasive species, are prohibited from being planted in the city.
b. Permitted Plants. Landscaping materials installed shall include species native to the Puget Sound lowland region of the Pacific Northwest or noninvasive species that have adapted to the climactic conditions of the region. Drought-tolerant or drought-resistant vegetation is preferred.
2. Plant Variety. Plant material should include a variety of seasonal colors, forms, and textures that contrast or complement each other with a mixture of evergreen and deciduous trees, shrubs, and groundcover and low-maintenance perennials. Preference must be given to plant material which can be maintained in its natural form without pruning over material requiring regular pruning or plants pruned into artificial shapes. Continuous expanses of uniform landscape treatment along an entire street front should be avoided.
C. General Tree Standards.
1. Trees must be selected from the city’s Tree Preservation and Protection Guidelines and meet the following standards:
a. A mixture of deciduous and evergreen trees must be planted in all landscaped areas of a site with exceptions noted in the specific landscaping sections of this chapter.
b. Trees must be suitable to the site and, if applicable, provide adequate screening throughout the entire life of the tree.
c. Deciduous and evergreen trees must be a minimum of eight feet in height and have a caliper size of at least two inches at time of planting.
d. Trees must be planted so that, when they reach maturity, there will be a minimum of 10 feet of clearance on-center between trees.
e. Tree selection within all landscape areas, including street trees, must comply with Snohomish PUD utility requirements, other existing utilities (stormwater, water, and wastewater conveyance systems), lighting, existing and proposed signage, adjacent trees, existing natural features, tree root growth, solar access, planting area width, and overall height of selected trees at maturity.
f. Trees must be arranged to promote energy conservation wherever practical: This includes using deciduous trees on the south and west sides of buildings to provide shade from summer sun and evergreen trees on the north side of buildings to dissipate effects of winter wind and rain.
g. Tree branches must be trimmed to provide a minimum of six feet of clearance measured from the ground to the branch to prevent sight and pedestrian obstructions. Tree branches must be trimmed to provide eight feet of clearance when overhanging vehicular use areas.
h. If more than 10 trees are required to be installed, no more than 40 percent of the new trees may be of a single species. This applies to the new trees to be planted, not to the existing trees on the site.
i. The specific number of trees required for a landscaped area on a site may be found under the respective section of this chapter.
j. Trees may be planted in linear rows, staggered rows, or clustered. However, all trees shall be planted a minimum of five feet on-center from back of public sidewalk edge.
2. In several sections of this chapter, a specific number of trees are required per linear feet of landscape area. Trees are categorized in the city’s Tree Preservation and Protection Guidelines into three types: small, medium, and large. If an applicant desires to use a combination of types, the applicant must first calculate how many small trees would be required by this chapter. Small trees may be substituted for medium or large trees and large or medium trees may be substituted for small trees according to the table below:
D. General Shrub and Groundcover Standards.
1. Groundcover. All areas of exposed earth not covered by trees or other plants must have living groundcover installed unless otherwise permitted.
2. Motorist Visibility. In driveway and roadway sight triangles and parking lot frontage strips, shrubs and groundcover must be composed of low evergreen shrubs or a mix of evergreen and non-evergreen shrubs with a maximum growth height of three feet.
3. Nonliving Groundcover. Nonliving groundcover (noncompacted, unless a functional part of a LID system) may not be used as living groundcover substitutes. However, up to three percent of the site’s entire landscaped area may be landscaped with nonliving groundcover. Nonliving groundcover may not be installed within three feet of pedestrian walkways.
4. Landscape Areas Abutting Parking Stalls. If curbing or wheel stops are installed along an edge of a parking space that abuts a landscaped area, groundcover or plants may be installed adjacent to the stall. Otherwise a minimum area of two feet from the pavement edge shall be free of plants or shrubs. Grasses or groundcover may be planted in this area.
E. General Fence and Hedge Standards.
1. Vision-Obscuring Fences and Hedges. Fences are required in several landscaping types described in this chapter. The standards for fences and hedges must meet any applicable requirements in Chapter 21.10 LMC.
a. Exceptions. The following exceptions apply:
i. Height of fences or shrub hedges must be limited to maximum six-foot height in buffer landscape and frontage landscape areas.
ii. Where a fence is required or used to meet vision-obscuring purposes, a new fence shall not be required in those cases where a fence already exists which meets the intent of this section. However, if the existing fence is ever removed, demolished or partially destroyed, then the owner of the property shall be required to replace the fence at that time in accordance with the requirements of this code.
iii. In those cases where the slope of the land is such that the location of a fence required by this code is impractical or ineffective in satisfying the intent of this section, the development and business services director may, at his discretion, permit a location which more adequately satisfies the intent of this section.
F. General Pedestrian Walkway and Sight Triangle Standards.
1. Pedestrian connections and walkways may traverse landscaped areas. All areas of a landscape buffer strip must be landscaped except where occupied by a pedestrian sidewalk, path, or vehicular driveway.
2. Pedestrian connections are encouraged across landscaped areas to connect multifamily and single-family residential zones, to commercial zones, and between commercial zones, for ease of resident access to grocery, retail, and other commercial businesses. Such pedestrian connections must be no wider than five feet.
G. Low Impact Development (LID) Facilities and Landscaping.
1. The city encourages landscaping to utilize low impact development (LID) practices where feasible. Applicants that incorporate these features may count them towards required landscaping and tree planting requirements.
2. LID Facilities. Areas of vegetation planted in stormwater LID facilities (except for permanently flooded or ponded areas) and for which there is a city-approved maintenance plan, as prescribed in the city’s Engineering Design Standards Manual, may count towards:
a. The minimum landscape coverage areas per the landscaping requirements outlined in the zone’s appropriate design standards; or
b. The minimum landscaped area required in the buffer landscaping strip as per this chapter; or
c. The minimum parking lot or parking structure buffer landscaping strip pursuant to LMC 21.08.350.
H. Existing Natural Vegetation Preservation.
1. Existing naturally vegetated areas may be retained and count towards landscaping standards based on location of the naturally vegetated area, species of trees, diameter at breast height of trees, and types of existing understory plantings.
a. The existing naturally vegetated area must meet or exceed the minimum number of trees (in any combination of large, medium, or small from the Lynnwood Tree Preservation Guidelines) that would otherwise be required for buffer landscaping.
b. Any invasive or noxious weed plant species as described in subsection (B) of this section or diseased, dead, or dying trees must be removed prior to installation of supplemental plantings.
c. Supplemental Plantings. The city may require the applicant to plant trees, shrubs, and groundcover according to the requirements of this section to supplement existing vegetation and provide adequate buffer between properties.
d. An identified critical area buffer that encroaches into or overlaps the site’s required general site landscaping area or landscape buffer area may be counted where it overlaps the area required to be covered by general landscaping or buffer landscaping requirements.
e. Protection Techniques. The applicant must use the protection techniques described in LMC 17.15.160(B) to ensure protection of existing trees and soil on construction sites.
2. The existing naturally vegetated area must be delineated on the landscaping plan and must meet the following criteria:
a. For general site landscaping areas and buffers, credit for existing natural areas must be based on the existing trees in the naturally vegetated area. The number of new trees required may be reduced by two for every one existing tree preserved in the existing natural area.
b. In order for existing trees to be counted they must be listed in the City Recommended Tree List and have a minimum diameter at breast height (DBH) of eight inches.
c. Trees listed in the table “Trees Not Recommended” in the Lynnwood Tree Preservation Guidelines shall not be credited towards the required number of trees for a general or buffer landscape area.
d. Existing trees with a DBH of less than eight inches shall not count towards credit for landscaping but must not be removed unless tree health is assessed in accordance with subsection (H)(2)(e) of this section.
e. Existing tree health must be assessed by an ISA certified arborist with tree risk assessment qualification (TRAQ). Only healthy trees must be shown for preservation on the landscape plan. Diseased, dying, dead, or overcrowded trees too closely spaced for adequate tree health must be marked for removal on the plan by the qualified landscape professional, licensed arborist or horticulturalist.
f. Existing trees that meet the required DBH in the naturally landscaped areas shall be identified on the landscape plan and listed in a table showing DBH, species, and health status on the landscape plan.
g. At least 75 percent of the ground surface of the naturally landscaped area must be covered with existing natural, living, vegetated groundcover, shrubs, or plants.
h. The licensed arborist or horticulturalist must identify the existing groundcover, shrubs, or plants and show the various areas of predominant groundcover on the landscape plans using differentiating fill patterns. Identified species of the predominant groundcover must be included in the table. Estimated coverage area of the groundcover, shrubs, or plants must be totaled and expressed as a percentage of the entire ground surface area of the naturally vegetated area.
3. The development and business services director or designee may approve a natural vegetated area with fewer trees or less groundcover than required; provided, that if it is a buffer area, the natural vegetation must provide the same amount of buffering between zones or a parking area and adjacent property, as required in this chapter.
I. Xeriscaping. Xeriscape is a process by which sound horticultural, landscaping, and efficient water-using principles come together to provide an attractive, but low maintenance, and low water using landscape. Xeriscaping styles can be quite variable depending on the suitability of low water use plants for the region’s climate.
1. Xeriscaping shall meet the following four principles:
a. Good Design. Design should be based on careful selection of low water use plants or drought-tolerant plants;
b. Soil Improvement. Improvements including the addition of manure, compost, or other organic materials which can be amended into the soil should be used;
c. Limited Lawn Areas. Minimizing high water use grass areas results in minimal lawn maintenance; and
d. Efficient Water Use. Drip irrigation systems are preferred. Water between 12:00 midnight and 6:00 a.m. to lower the evaporation rate of water.
2. Low water use varieties of turf must be used. High water use turf must be limited to no more than 25 percent of the landscaped area and remaining landscaped area must be of low water or drought-resistant turf varieties, groundcover, native grasses, shrubs, or trees.
3. Plants and trees selected for low water use shall be well-suited to the climate, soils, and topographic conditions of the site and must be low water use plants once established.
4. Low water use or drought-resistant trees appropriate to the Puget Sound lowland region of the Pacific Northwest must be selected (use the Lynnwood Tree Preservation and Protection Guidelines or the Washington State University (WSU) hardy plants for waterwise landscapes list for guidance).
5. Plants with similar water use requirements must be grouped together in distinct hydrozones and be irrigated with appropriate levels of water.
6. Up to six inches of mulch may be used in limited areas around young plants to assist them with gaining root structure while they establish themselves.
7. Plants and trees with a variety of textures, colors, and profiles must be used to create visual interest. (Ord. 3399 § 2 (Exh. A), 2021; Ord. 3326 § 2, 2019)