2.8.1 BMP S143 - Landscaping and Lawn/Vegetation Management
This BMP applies to all properties and areas of the ROW that have landscaping and/or lawn areas. Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer application, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides.
Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests with chemical pesticides and is conducted commercially at commercial, industrial, and residential sites. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; sap stain and insect control on lumber and logs; rooftop moss removal; killing nuisance rodents; fungicide application to patio decks; and residential lawn/plant care. Toxic pesticides such as pentachlorophenol, carbamates, and organometallics can be released to the environment by leaching and dripping from treated parts, container leaks, product misuse, and outside storage of pesticide contaminated materials and equipment. Poor management of the vegetation, poor application of pesticides or fertilizers, and non-targeted irrigation water or overwatering can cause appreciable stormwater contamination.
Install engineered soil/landscape systems to improve the infiltration and regulation of stormwater in landscaped areas. Apply BMP L613 - Post-Construction Soil Quality and Depth BMPs as required per Minimum Requirement 5 - Onsite Stormwater Management.
Do not dispose of collected vegetation into wetlands, waterways or the stormwater system.
Select the right plants for the planting location based on proposed use, available maintenance, soil conditions, sun exposure, water availability, height, site factors, and space available.
Ensure that plants selected for planting are not on the noxious weed list. The Washington State Noxious Weed List can be found at: https://www.nwcb.wa.gov/printable-noxious-weed-list
Do not blow vegetation or other debris into the stormwater system.
Dispose of collected vegetation such as grass clippings, leaves, and sticks by composting or recycling.
Use manual and/or mechanical methods of vegetation removal (pincer-type weeding tools, flame weeders, or hot water weeders as appropriate) rather than applying herbicides, where practical.
Use at least an 8" topsoil layer with at least 8% organic matter to provide a sufficient vegetation-growing medium.
Organic material is at the least water-soluble form of nutrients that can be added to the soil. Composted organic matter generally releases only between 2 and 10 percent of its total nitrogen annually, and this release corresponds closely to the plant growth cycle. Return natural plant debris and mulch to the soil, to continue recycling nutrients indefinitely.
Select the appropriate turfgrass mixture for the climate and soil type.
Certain tall fescues and rye grasses resist insect attack because the symbiotic endophytic fungi found naturally in their tissues repel or kill common leaf and stem-eating lawn insects.
The fungus causes no known adverse effects to the host plant or to humans.
Tall fescues and rye grasses do not repel root-feeding lawn pests such as Crane Fly larvae.
Tall fescues and rye grasses are toxic to ruminants such as cattle and sheep.
Endophytic grasses are commercially available; use them in areas such as parks or golf courses where grazing does not occur.
Local agricultural or gardening resources such as the Washington State University Extension office can offer advice on which types of grass are best suited to the area and soil type.
Use the following seeding and planting BMPs, or equivalent BMPs, to obtain information on grass mixtures, temporary and permanent seeding procedures, maintenance of a recently planted area, and fertilizer application rates: BMP C120 - Temporary and Permanent Seeding, BMP C121 - Mulching, BMP C123 - Plastic Covering, and BMP C124 - Sodding.
Adjusting the soil properties of the subject site can assist in selection of desired plant species. Consult a soil restoration specialist for site-specific conditions.
2.8.1.3 Recommended Additional BMPs
Conduct mulch-mowing whenever practicable.
Use native plants in landscaping. Native plants do not require extensive fertilizer or pesticide applications. Native plants may also require less water.
Till a topsoil mix or composted organic material into the soil to create a well-mixed transition layer that encourages deeper root systems and drought-resistant plants.
Apply an annual topdressing application of 3/8" compost. Amending existing landscapes and turf systems by increasing the percent organic matter and depth of topsoil can:
Substantially improve the permeability of the soil.
Increase the disease and drought resistance of the vegetation.
Reduce the demand for fertilizers and pesticides.
Disinfect gardening tools after pruning diseased plants to prevent the spread of disease.
Prune trees and shrubs in a manner appropriate for each species.
If specific plants have a high mortality rate, assess the cause and replace with another more appropriate species.
When working around and below mature trees, follow the most current American National Standards Institute (ANSI) ANSI A300 standards and Internationl Society of Arboriculture BMPs to the extent practicable.
Monitor tree support systems (stakes, guys, etc.).
Repair and adjust as needed to provide support and prevent tree damage.
Remove tree supports after one growing season or maximum of 1 year.
Backfill stake holes after removal.
When continued, regular pruning (more than one time during the growing season) is required to maintain visual sight lines for safety or clearance along a walk or dive, consider relocating the plant to a more appropriate location.
Make reasonable attempts to remove and dispose of Class C noxious weeds.
Reseed bare turf areas until the vegetation fully covers the ground surface.
Watch for and respond to new occurrences of especially aggressive weeds such as Himalayan blackberry, Japanese knotweed, morning glory, English ivy, and red canary grass to avoid invasion.
Aerate lawns regularly in areas of heavy use where the soil tends to become compacted. Conduct aeration while the grasses in the lawn are growing most vigorously. Remove layers of thatch greater than ¾" deep.
Set the mowing height at the highest acceptable level and mow at times and intervals designed to minimize stress on the turf. Generally mowing only 1/3 of the grass blade height will prevent stressing turf.
Mowing is a stress-creating activity for turfgrass.
Grass decreases its productivity when mowed too short and there is less growth of roots and rhizomes. The turf becomes less tolerant of environmental stresses, more disease prone and more reliant on outside means such as pesticides, fertilizers, and irrigation.