Roadside Revegetation

IMPLEMENTATION GUIDES
and covering the seeds with hydromulch with a second pass. The thin seed cover is favorable
for only small seeded species. Seeds can be damaged in the hydroseeding operations through
the pumps and agitators, or by hitting the ground at very high speeds during application.
Even with these limitations, hydroseeding is still one of the most common methods of
applying seeds to road construction disturbances. It is often the only way to place seeds on
steep, rough terrain encountered in mountainous regions. Compensation for these limitations
has had varying degrees of success. Possible variations include (1) increasing the amount of
seeds, (2) applying seeds in the first pass, then covering with hydromulch in the second pass,
and (3) applying higher rates of mulch. Fall hydroseeding also increases establishment rates.
Over- wintered seeds are ready to germinate on the first warm days of late winter or early
spring when humidity levels are high. In addition, hydraulic mulches are more likely to stay
moist for longer periods of time. Hydroseeding is simpler than dry seeding because there is
no seed metering system; seed mixes are simply mixed into the hydroseeder tank and applied.
See Section 10.3.2, Hydroseeding, for more discussion on hydroseeding.
Figure 10-94 | Seeds mixed
into long-fibered mulch
Seeds mixed into long- fibered mulch
have less contact with soil, which can
reduce germination.
Formulate Seed Mixes
The seed mix refers to the species composition being applied over a seeding area. It is
important to avoid applying a single species to a site. Since highly disturbed sites typically are
extremely variable in soil temperatures, fertility, soil moisture, solar radiation, and other site
factors, it is important to apply a number of species in a seed mix to assure that all possible
microsites are populated (Monsen and Stevens 2004). Microsites that are unfavorable to one
species might be favorable to others. Applying a mix of species also assures that if there is a
problem with the germination of one species, the other species will fill in. The composition
of seed mixes and sowing rates should be based on the growth habits of each species and
the soils and climate of the site.
It is preferable to avoid mixing slow-growing species with fast growers, because the fast
growers will out-compete the slow growers for space and resources (Monsen and Stevens
2004). Separating slow growers from fast growers is not always possible. The seed quantities
must therefore reflect higher ratios of slow growers to fast growers to achieve some degree of
success. Shrubs and trees are typically less aggressive than grasses during the establishment
phase, and should be applied in a separate mix or planted as seedlings. Grasses tend to be
more aggressive than forbs. However, if the Truax® seed drill is used, they could be applied in
the same area but in different rows using the separate seed boxes. Some species take several
years to develop. A mixture of fast-growing annuals and slow-growing perennials will assure
that there is cover the first year, yielding to more robust perennials in the succeeding years.
Disturbed reference sites can be good indicators of species that are adapted to the climate and
soils of the project area. Vegetative surveys conducted during the planning stages should show
the proportions of species that can be expected, and these findings should become the basis
for developing species composition and ratios of each species. Prior to determining sowing
rates, the proportion of each species within each seed mix should be set. This information
will be used to determine seeding rates for each species.
Figure 10-95 | Seeds
applied in hydromulch
Applying seeds in a hydromulch places a
portion of seeds on the soil surface and
some suspended in the hydroseeding
matrix above the surface.
Determine Sowing Rates
The sowing rate is the amount of seeds of each species in a seed mix that are applied in a
given area. Sowing rates are calculated for each species that compose a seed mix. These
calculations are performed twice – once during the development of seed increase contracts
to obtain an approximate quantity of seeds to propagate for the entire project, and several
months prior to actual seeding when seed inventories are known and exact seeding areas
are located. The calculations made prior to seeding will be used to assemble the seed mixes
for each seeding area.
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
332