18J.15.110 Plant Sizes, Soil Amendment, Mulching and Irrigation.
The purpose of this Section is to address water conservation measures by using appropriately-sized plantings in landscapes and smart irrigation design for sustainable landscapes with techniques that conserve, recycle, and reuse the resources that are invested.
A. Applicability. The following plant sizes and irrigation methods apply to street trees, landscape buffers, noise-attenuating barriers, and parking lot landscaping, unless a standard has otherwise been specified in this Chapter.
B. Design Objective. Plant vegetation that, with minimal irrigation, will survive and provide aesthetic relief from developed portions of the project site. Provide needed irrigation for vegetation to ensure survivability and vibrant health for the life of the project.
C. Standards.
1. Refer to PCC 18J.15.100, Plant Lists, for required plant selection standards.
2. Plant Sizes.
a. Trees, evergreen. Tree material at time of planting shall be of a sufficient size to meet the minimum height and screening requirements of the landscape level within 10 years of installation.
b. Trees, deciduous. Tree material at time of planting shall be of a sufficient size to meet the minimum height and screening requirements of the landscape level within 10 years of installation.
c. Shrubs and Hedges. Shrub and hedge material at time of planting shall be of a sufficient size to meet the minimum height and screening requirements of the landscape level within 5 years of installation.
d. Groundcover, vegetative. Groundcover, other than lawn or turf grass, shall be planted to achieve minimum planting area coverage of 50 percent of required coverage within two years of installation and shall achieve 100 percent of required coverage within five years of installation. English ivy is not permitted.
e. Groundcover, inert. Wood chips, bark, decorative rock, or other appropriate inert organic material may be used.
f. Lawn, sod, and seed. If utilized in the landscape, newly-seeded lawns or installed sod shall include drought-resistant and hardy varieties that, when properly installed and maintained, can survive under conditions of restricted water use.
g. Berms. Mounds of earth used for berming shall not exceed a slope of 2 horizontal feet to 1 vertical foot (2:1).
3. Soil Amendment.
a. Landscape areas shall be deep tilled to a depth of at least 12 inches to facilitate deep water penetration and soil oxygenation. Use of soil amendments is encouraged to improve water drainage, moisture penetration, soil oxygenation, and/or water holding capacity. Soil amendments are organic matter, such as composted yard waste, sewer biosolids, and forestry by-products, but do not include topsoil or any mix with soil as an element. Sphagnum moss is not allowed because it provides only short-term value and is a non-renewable resource.
b. For all newly landscaped areas, including single-family residences, organic matter (3 to 4 cubic yards of organic matter per 1,000 square feet of landscape area) shall be incorporated to a depth of at least 4 inches.
c. For newly landscaped areas where topsoil is limited or nonexistent, or where soil drainage is impeded due to subsurface hardpan, 6 to 24 inches of sandy loam topsoil shall be spread in all planting and turf areas, in addition to the incorporation of organic matter into the top horizon of the imported soil.
d. Soil analysis of new or renovated turf areas shall include a determination of soil texture, including percentage of organic matter, an approximated soil infiltration rate, and a measure of pH value.
4. Mulching.
a. Mulch shall be applied regularly to, and maintained in all, planting areas to assist soils in retaining moisture, reducing weed growth, and minimizing erosion.
b. Mulches shall be applied at the following depths: 3 inches over bare soil, and 2 inches where plant materials will cover.
c. Acceptable mulches include organic materials, such as wood chips and shredded bark and inert organic materials such as decomposed lava rock, cobble, and gravel.
d. Non-porous materials, such as plastic sheeting, are not allowed in any area of the landscape because of down-slope erosion and potential soil contamination from herbicide washing.
5. Irrigation.
a. All landscaped areas must have installed a permanent underground irrigation system with an automatic controller plus an overriding rain switch, or an alternative irrigation method that provides enough water to ensure that the plants will establish and remain healthy.
b. Irrigation shall be permanent unless the plant materials selected are determined to be drought-tolerant, in which case irrigation shall be required until the plants are fully established and there shall be an identified method to easily provide water to the plants in the case of a prolonged drought.