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REBUILDING CALIFORNIA - Senate Bill 1
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Big Sur Slide
The primary goal of erosion control is to:
Vegetation helps Caltrans meet Stormwater management goals by protecting the soil surface from raindrop impact erosion, sheet flow erosion, and wind erosion. As plant roots work their way deep into the soil, and as the organic material produced by plants restores the soil, infiltration increases and stormwater runoff is greatly reduced.
In selecting plant material to control erosion, designers ought to try to maximize all the potential environmental benefits of roadside planting. Because roadside planting is linear, adding pollinator friendly plants to the roadside can help restore transportation corridors for pollinators and other wildlife. For example, adding pollinator friendly plants to roadside erosion control mixes could increase the pollinator population in California by closing gaps in the corridors that connect butterfly breeding grounds along the coast with their winter homes in Arizona, Nevada, Oregon and Washington. A diverse seed mix that can address a variety of environmental problems (erosion control and pollinator propagation) is always preferable to a planting palette that only addresses a single enviromental issue.
Don't forget the concept of ecological succession when selecting seed species. The most successful plant species for a project site will change over time in response to competition from other species, changes in soil structure, and other factors. Many disturbed sites are initially "colonized" by annuals and grasses and later support a more diverse cover of perennials, woody shrubs and large trees. Because of the uncertainty of exactly which plants will thrive on a project site, many designers select a plant palette that provides both immediate cover (annuals and grasses) as well as long-term cover (perennials, woody shrubs and trees).
Based upon your site analysis, reference site visit, and identified project goals and objectives, assemble a seed species mix. A typical seed mix might contain the following:
There are a number of excellent online tools available to help identify seed species that meet project success criteria and are well suited to a particular geographic/climatic region.
Lists of "pollinator friendly" seed species are available online at:
TransPLANT is useful for identifying potential seed mixes. Built upon the U.S. Forest Service ecoregion classification system, TransPLANT provides a designer with a list of potential seed mixtures, based upon project District, County, Route and Post Mile information.
When all else fails, a designer can always default to seed mixtures that have proven successful in the past. Before relying on this approach, keep in mind that past use of a particular seed species does not ensure that it is necessarily the right plant for your project. Remember to evaluate your seed species with regard to previously identified project goals and objectives. With this caveat in mind, here is Caltrans Most Commonly Used Seed Species List.
It is recommended to NOT specify seed species known to have a shelf life of less than six months. Short shelf life species may be required via an environmental regulatory agency. However, species will not germinate and will not meet permit requirements as intended. A good general rule is to avoid specifying short shelf life species. Here is a list of short shelf life species available on this website.
After selecting a seed species mix, the next step is to determine an appropriate application rate for these seed species. In general, the goal here is to determine the appropriate number of mature plants per square foot, and then convert this number into pounds of seed/acre. Refer to “Commonly Used Seed Species” to convert from seeds/ft2 to lb/ac.
This simple calculation will figure the amount of seed to plant 100% pure live seed.
You will need to know
The information and exercise below should provide you with enough information to determine an appropriate seed application rate to fill out your erosion control specifications.
Dormancy - natural protective mechanism to extend seed life
Germination - % of seed able to grow into normal plants when given favorable conditions
Specifying a higher minimum germination will typically increase seed costs. Specifying a lower minimum germination requirement may lower seed costs by result in increased weed cover. You may want to specify a higher minimum germination requirement for weed-sensitive projects.
Hard Seed - seed with external dormancy from a hard seed coat
Purity - % by weight of desired seed
Pure Live Seed (PLS) - quantity of live seed in a seed lot that will germinate. The remainder may be weed, debris, and non-viable seed. PLS = % germination x % purity/100
Viability - condition of the seed embryo being alive
Total viable seeds - germination + dormant + hard seed
We want a seed density of 100 seeds/ft2 for our site. The seeds will be hydroseeded or hand seeded (same recommended application rate, 80 – 100 seeds/ft2). Calculate the application rate (lb PLS/ac) for the seed mix listed in Table 1.
Total seed density = 100 seeds/ft2
1 acre = 43,560 ft2
Desired seeding density
Average pure seed weight
lb PLS/ac = Seed density (seeds/ft2) x 43,560 ft2/ac
Avg pure seed weight (seeds/lb PLS)
Lotus purshianus: 11 seeds/ft2 x 43,560 ft2/ac = 4.4 lb PLS/ac
108,500 seeds/lb PLS
Nassella cernua: 11 seeds/ft2 x 43,560 ft2/ac = 2.2 lb PLS/ac
215,200 seeds/lb PLS
Bromus carinatus: 23 seeds/ft2 x 43,560 ft2/ac = 13.8 lb PLS/ac
72,600 seeds/lb PLS
Repeat for the remaining species (see Table 2 for results).
Total seed application rate on the Erosion Control Legend should be 33.0 lb PLS/ac.
Use the seed species identified in Step 3 together with the application rate determined in Step 4 to complete the project Hydroseed and Hydromulch,Straw or Drillseed portion of the erosion control legend.
Updated April 13, 2018
Planning & Design
Improve Soil Health
Improve Soil Health & Provide Cover
Long Term Cover
Steep Slope Techniques
Low Impact Development
California Department of Transportation
Division of Design
1120 N Street
Sacramento, CA 95814
California Department of Transportation
Division of Design
P. O. Box 942874
Sacramento, CA 94271-0001
Design Liaison Phone List
Division of Design Org Chart