Chapter 3. Performance Criteria for Urban BMP Design ................... Stormwater Wetlands
3.23
The optimal depth requirements for several common species of emergent wetland plants are
often six inches of water or less.
To add diversity to the wetland, 5 to 7 species of emergent wetland plants should be used,
drawn from the suggested species listed in Appendix A. Of these, at least three species should
be selected from the "aggressive colonizer" group (e.g., bulrush, pickerelweed, arrow arum,
three square and rice cutgrass) (MDE, 1986).
The wetland area should be sub-divided into separate planting zones of more or less constant
depth. Approximately half the wetland surface area should be planted. One plant species
should be planted within each flagged planting zone, based on their approximate depth
requirements. Plants should be installed in clumps with individual plants located an average of
18 inches on center within each clump. Individual plants should be spaced 12 inches to 24
inches on center.
Post-nursery care of wetland plants is very important in the interval between delivery of the
plants and their subsequent installation, as they are prone to desiccation. Stock should be
frequently watered and shaded while on-site.
A wet hydroseed mix should be used to establish permanent vegetative cover in the buffer
outside of the permanent pool. For rapid germination, scarify the soil to ½ inch prior to
hydroseeding. Alternatively, red fescue or annual rye can be used as a temporary cover for the
wet species.
Because most stormwater wetlands are excavated to deep sub-soils, they often lack the
nutrients and organic matter needed to support vigorous growth of wetland plants. At these
sites, three to six inches of topsoil or wetland mulch should be added to all depth zones in the
wetland from one foot below the normal pool to six inches above. Wetland mulch is preferable
to topsoil if it is available.
The stormwater wetland should be staked at the onset of the planting season. Depths in the
wetland should be measured to the nearest inch to confirm the original planting zones. At this
time, it may be necessary to modify the pondscape plan to reflect altered depths or the
availability of wetland plant stock. Surveyed planting zones should be marked on an “as-built”
or design plan and located in the field using stakes or flags.
The wetland drain should be fully opened at least three days prior to the planting date (which
should coincide with the delivery date for the wetland plant stock).
Wetland mulch is another technique to establish a plant community that utilizes the seedbank of
wetland soils to provide the propagules for marsh development. The majority of the seedbank