A. Plant Selection: Plants shall be well-suited to the microclimate and soil conditions at the project site. Native, locally adaptable and environmentally sustainable plants are acceptable. See the Washington County Water Conservancy District’s recommended plant list on wcwcd.org. Plants with similar water needs shall be grouped together as much as possible into hydrozones for efficient irrigation. Invasive plant species as identified by the county shall not be planted.
1. Areas with slopes greater than 25% shall be landscaped with deep-rooting, water-conserving plants that do not include grass.
2. Park strips and other landscaped areas less than eight (8) feet wide shall be landscaped with water-conserving plants and/or mulch that do not include grass. All Planting Beds must have mulch on the soil surface with exceptions for areas being restored to appear as a native desert.
3. All Planting Beds shall have mulch on the soil surface with exceptions for areas being restored to appear as a native desert.
B. Tree Selection and Irrigation: Tree species shall be selected based on growth characteristics and site conditions, including available space, overhead clearance, soil conditions, exposure, and desired color and appearance. Trees shall be suited for water-efficient landscapes. Trees shall be irrigated on a separate hydrozone as needed for efficient irrigation, and to allow for watering under water-shortage conditions when other plant material may not be watered due to drought conditions. Trees shall be selected and planted in accordance with the following county guidance:
1. Broad canopy trees shall be selected where shade or screening of tall objects is desired;
2. Low-growing trees shall be selected for spaces under utility wires;
3. Select trees from which lower branches will be trimmed to maintain a healthy growth habit where visual clearance and natural surveillance is a concern;
4. Narrow or columnar trees shall be selected for small spaces, or where awnings or other building features limit growth, or where greater visibility is desired between buildings and the street for natural surveillance;
5. Tree placement shall provide canopy cover (shade) and avoid conflicts with existing trees, retaining walls, above and below ground utilities, lighting, and other obstructions; and
C. Maintenance: All areas required to be landscaped shall be maintained in a live and thriving condition. Such areas shall be mowed, trimmed, fertilized, and edged, and free from dead plants, weeds, litter or debris, in compliance with regionally accepted horticultural practices.
D. Irrigation Design Standards:
1. Pressure Regulation. A pressure regulating valve shall be installed by the builder or developer, and maintained by the owner, if the static service pressure exceeds 90 pounds per square inch (psi). The pressure-regulating valve shall be located between the meter and the first point of water use, or first point of division in the pipe, and shall be set at the manufacturer’s recommended pressure for the sprinklers.
2. Irrigation Controller. It is required that landscaped areas use a WaterSense labeled smart irrigation controller, or a similar weather-based controller if an appropriate WaterSense model is not available, which automatically adjusts the frequency and/or duration of irrigation events in response to changing weather conditions. All controllers shall be equipped with automatic rain delay or rain shut-off capabilities and have memory retention capability to retain pre-programmed irrigation schedules. Sites are not exempt from water waste prohibitions.
3. Where lawns are allowed, spray irrigation may be used. To the extent possible, spray irrigation should be free from obstructions.
4. Each valve shall irrigate a landscape with a similar site, slope and soil conditions, and plant materials with similar watering needs. Grass, trees and non-grass areas shall be irrigated on separate valves. Drip emitters and sprinklers shall be placed on separate valves.
5. Low-volume irrigation equipment (i.e., drip emitters, bubblers) shall be provided for each tree.
6. Drip irrigation shall be used to irrigate plants in non-grass areas. Drip system shall be equipped with a pressure regulator filter, flush-end assembly and emitters rated for 20 gallons per hour (gph) or less. Spray head to drip conversion for rehabilitated landscape sites may be acceptable with county approval of Irrigation Plans.
7. High conservation efficiency spray nozzles are required for sprinkler applications.
8. Sprinkler heads shall have matched precipitation rates with each control valve circuit.
9. Sprinkler heads shall be attached to rigid lateral lines with flexible material (swing joints) to reduce potential for breakage.
10. Check valves are required. Pressure compensating valves and sprinklers are required where a significant variation in water pressure occurs within the irrigation system due to elevation differences.
11. Filters and end-flush valves shall be provided for drip irrigation lines if pumped or secondary irrigation water is utilized.
12. Landscape watering with potable (treated) water is prohibited from 10 a.m. to 8 p.m., from June 1 to September 1, to maximize irrigation efficiency.
13. Water waste is prohibited. Waste includes overwatering, irrigating during a precipitation event, water that sprays or flows off the property, failure to comply with drought restrictions and/or a failure to repair irrigation system leaks and/or malfunctions in a timely manner.
Overwatering can be avoided by following the water district’s recommended irrigation schedule and practices as noted on wcwcd.org. The generally recommended schedule is:
a. Winter (Nov - Feb) - sprinkler and drip irrigation up to 1 day a week. Irrigation is typically not needed in December, January and February.
b. Spring (Mar - April) - sprinkler irrigation up to 3 days a week and drip irrigation up to 2 days a week.
c. Summer (May - Aug) - sprinkler irrigation up to 4 days a week and drip irrigation up to 3 days a week.
d. Fall (Sept - Oct) - sprinkler irrigation up to 3 days a week and drip irrigation up to 2 days a week.
14. Program valves for multiple repeat cycles are required to reduce runoff on slopes and for soils with slow infiltration rates.
15. Backflow prevention devices that are permanently affixed are required to prevent backflow of chemicals or other contaminants from entering the potable water system, or other water sources in the area. Fertigation systems are not permitted without backflow prevention devices that are permanently affixed. (Ord. 2022-1206-O, 4-19-2022; amd. Ord. 2023-1246-O, 12-19-2023)