Roadside Revegetation

IMPLEMENTATION GUIDES
10.1.3 MULCHES
Introduction
Mulch is defined as a protective material placed on the soil surface to prevent evaporation,
moderate surface temperatures, prevent weed establishment, enrich the soil, and reduce
erosion. Mulches therefore have many functions or roles in the recovery of native vegetation
to a disturbed site. But confusion often arises around the use of mulches on revegetation
projects unless the reasons for using them in a project are clearly defined. In this discussion,
we have grouped mulches into four uses based on revegetation objectives:
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Seed Covering
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Seedling Mulch
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Soil Improvement
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Seed Supply
For most projects, mulches are used to meet more than one objective. Problems arise when
the methods for applying overlapping objectives are not compatible. For example, erosion
control objectives and seed covering objectives go hand-in-hand because the soil surface
needs to be stable for seeds to germinate and grow into young seedlings. In turn, the surface
ultimately becomes stable through the establishment of young plants. Yet erosion control
products and practices that are effective for controlling surface erosion are not always optimal
for establishing vegetation. For this reason, it is important to understand the objectives for
mulching and to integrate them into a comprehensive strategy when selecting mulch types
and application methods.
This section discusses the objectives for applying mulches and the potential mulch sources.
We have left the discussion of the effectiveness of mulches for erosion control and surface
stabilization to the many publications and research devoted to this topic and focus primarily
on the characteristics of mulches for plant establishment.
Seed Covering
One of the principal reasons for applying mulch is to enhance seed germination and early
seedling establishment. During this critical period, desirable mulches will:
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Protect seeds and young seedlings from soil splash, sheet erosion, and freeze-thaw
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Keep seeds moist during germination
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Moderate surface temperatures during germination
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Keep young seedlings from drying out
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Prevent salts from wicking to the surface and harming newly germinating seedlings
The characteristics of mulch materials that make ideal seed coverings are those that protect
seeds from drying winds, solar radiation, high evapotranspiration rates, and surface erosion
while still allowing seeds to germinate and grow through the mulch into healthy seedlings.
Long-fibered mulches, such as straw, wood strands, pine needles, and ground or chipped
wood, placed at the appropriate thickness, usually meet these characteristics. When applied
correctly, the strands of long-fibered mulch loosely bridge on top of each other, much like
“pick- up-sticks,” forming large air spaces or pores (Figure 10-13). Large pores function much
like the air spaces in building insulation by moderating extreme temperatures.
Compared to short-fibered mulches, such as hydromulch, long-fibered mulches can be applied
at greater thicknesses, which help maintain surface soil moisture and higher humidity around
germinating seeds and emerging seedlings. In addition, long-fibered mulches can mitigate
Figure 10-13 | Long-fibered mulches
Long-fibered mulches, like wood strands
shown below, create a good growing
environment because seeds and seedlings
are protected from excessive
drying during germination and early
seedling establishment. On sites where
freeze-thaw is prevalent, long-fibered
mulches can insulate the soil and protect
emerging seedlings.
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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