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Illinois Native Plant Guide - General Design, Application,& Management Considerations

Illinois Native Plant Guide

General Design, Application, & Management Considerations

Sources of Design Information
Slopes
Soils
Installation & Establishment
Water Levels
Irrigation
Seeding Rates
Cover Crops/Mulch/Erosion Blanket
Growth Rates
Fertilizer
Depredation
Naturally Invading Plant Species
Mowing and Prescribed Fire
Other Considerations


Sources of Design Information

The overall design of any stormwater management facility or streambank stabilization project is very important. If designed inappropriately, it will be very difficult, if not impossible, to establish native species. It will also be difficult to realize any of the water quality or habitat benefits. A brochure entitled Stormwater Detention Basin Retrofitting available from the Northeastern Illinois Planning Commission (NIPC) provides guidelines for incorporating best management practices (BMP) and native plantings into existing facilities. NIPC also has a course curriculum notebook for Urban Stormwater Best Management Practices for Northeastern Illinois and a Source Book: Natural Landscaping for Public Officials, which provide design guidelines and encourage the use of native plantings.

For streambank and shoreline stabilization methods and design information, Appendix A in the Streambank Stabilization Program report (RUST 1995) available from DuPage County Department of Environmental Concerns is a recommended reference. The latest edition of the Illinois Urban Manual (NRCS/IEPA) is also a good reference for design information and specifications. Bioengineering techniques are becoming increasingly popular nationwide and new information is continually appearing in the literature. The Illinois State Water Survey has done extensive work on streambank stabilization and can be contacted for further information or refer to “Field Manual of Urban Stream Restoration,” (Gaboury, et al., 1996) for more comprehensive stream restoration information. Other references may be available from your county Soil and Water Conservation District or from the local offices of the agencies that produced this Guide (See Appendix C). [back to top]


Slopes

In most stormwater management facilities and streambank projects attempting to use native vegetation, the most gentle slopes possible should be used. Steeper slopes magnify the erosive forces and make it more difficult to establish the plant material before a major erosion event damages or destroys the plantings. Gradual slopes (no steeper than 5:1 horizontal: vertical) are particularly important along the shorelines of ponds and detention basins. Most native plants are adapted to the gentle slopes that surrounded natural ponds and wetlands or were present along streams in the presettlement condition. Appropriate BMP’s for soil erosion and sediment control (see Illinois Urban Manual) should be used during construction at sites where native vegetation will be installed. [back to top]


Soils

The condition and type of soil at the site where native plants are to be established are also important factors. Many native species are widely distributed in the United States and naturally grow in many soil textures and soil types. For most users of this Guide, however, the soil present will not be a natural soil profile, but rather a regraded situation with topsoil placed on the site as a growth medium. Soil compaction is a common cause of failure in wetland restorations and other native plantings. Care must be taken to ensure that soil compaction is minimized so that the plant roots can obtain water and oxygen. A minimum of one foot of topsoil applied with the least compaction possible is recommended. A soil with a coarser texture (higher sand and silt content than clay) is recommended because it reduces the potential for compaction. A mineral soil with a high organic content is also recommended. Organic matter in the soil increases water holding capacity, reduces compaction potential, and provides plant nutrients. Care should also be taken to ensure that the soil used does not contain a large number of weed seeds that would compete with the native plantings. Organic soils, such as peat or muck, present special problems if their hydrology is modified and should be avoided above the water line if possible. [back to top]


Installation & Establishment

Detailed information is provided for each species on germination requirements and recommended establishment practices. Particular attention should be given to recommendations on seeding versus live plants or rootstock. There is no single best time to plant or seed. Generally, live plants and rootstock should be planted in the spring, approximately from last frost until mid-June. For seeding, fall or spring sowing are options. Spring seeding can be performed from March 1st through May. Fall seeding or dormant seeding can be performed after November 15. Some species are inhibited by fall planting while others are favored by fall planting. Summer seeding and planting in July, July, or August can be used if necessary, but only with adequate irrigation. Where specific information is available, this information is given within the establishment category for each species. The information provided assumes adequate seedbed preparation that includes a relatively smooth topsoil surface, free of stones, clods, sticks and other debris. Also please consult the section on soils. Recommendations are given with each species for seeding or planting method. [back to top]


Water Levels

Information is provided concerning water depth preferences and inundation tolerances for all species. This information should be used with the overall guiding principle that native plants are adapted to seasonal flooding and flooding of short duration. Prior to the intensified flooding problems brought on by urbanization, natural flooding occurred occasionally, but mostly in the spring with spring rainfall and snow melt. It did not occur with each major storm event throughout the summer, as occurs in many detention basins. Many native plants cannot tolerate the widely fluctuating water levels often associated with stormwater facilities. An effort should be made to reduce or dampen the water level fluctuations and flood plantings only for short durations during the growing season. It is also important to keep in mind that many mature wetland plants can survive flooding or inundation, but the seedlings cannot. Natural marshes go through an annual draw-down cycle as well as during droughts to allow germination of new plants, which allows these seedlings to become established. Provision should be made to lower the water levels during the critical establishment period. [back to top]


Irrigation

While established deep-rooted native plants are generally drought resistant, some irrigation of new plantings may be needed. If initial seeding or planting is followed by a dry period, irrigation may be required until the plants are fully established and can withstand a drought. Irrigation should be performed in a manner that does not erode the soil or wash away the seed. [back to top]


Seeding Rates

Seeding rates for any species depends on the mix of species, setting, and desired result. In order to establish a dense, single-species stand, seeding rates would be heavier than that needed for a mixed species planting. Many plant vendors and installation contractors do not provide seeding rates in their catalogs as they want to adapt rates to each site or they consider rates “trade secrets.” Seeding rates provided in this Guide are ranges taken from three local sources that have experience in the establishment of native plantings in northeastern Illinois. Consideration of the setting, goals and objectives, and best professional judgement should be used in determining final seeding rates for any given project. This information applies only to those species where seeding is appropriate and does not apply to rootstock, transplant, or other planting methods. In these cases, seeding rates are shown as “Not Applicable.” Seeding rates listed as “Not Available” are listed as such because the source references used did not contain seeding rate information for all species. All rates are pure live seed (PLS). [back to top]


Cover Crops/Mulch/Erosion Blanket

Most native vegetation installation contractors will recommend that a cover crop or mulch be used. A cover crop is a crop of quick germinating species that will serve to hold and stabilize the soil until the desired permanent vegetation is established. Mulch is a natural or artificial layer of suitable materials that aid in soil stabilization and soil moisture conservation which provides microclimatic conditions suitable for germination and growth. Both techniques are recommended for temporary soil erosion control measures. They also can provide a temporary fuel matrix to allow prescribed burning before the native vegetation is fully established. Typically, cover crops consist of nonnative species. Any cover crop used should be composed of nonpersistent species so that it is in fact only a temporary cover crop and is eventually replaced by the desired native vegetation. Many contractors have strong preferences on cover crop composition. Recommended species frequently included are: annual ryegrass (Lolium multiflorum), red top (Agrostis alba), timothy (Phleum pratense), wild ryes (Elymus spp) (native), oats (Avena sativa), barley (Hordeum vulgare), rye (Secale cereale) and others. Some native species such as smartweeds (Polygonum spp), rice cut grass (Leersia oryzoides), and barnyard grass (Echinochloa crusgalli) can also serve this purpose. Species that will persist and compete with the desired native vegetation such as Hungarian or smooth brome (Bromus inermis), Kentucky bluegrass (Poa pratensis), and fescue (Festuca spp) should be avoided. Properly applied nonallelopathic mulch or erosion control blanket should be used on steeper slopes. Erosion control blankets are recommended on detention basin side slopes and in vegetated swales where flowing water is present. Some native species require light for germination. This should be considered when selecting either a cover crop, mulch, or erosion blanket. [back to top]


Growth Rates

It may appear that many of these native plants are very slow growing, as reported in some landscape literature sources. It should be noted, however, that for most native plants the strategy is to grow a deep root system before putting energy into above-ground growth. While it may appear that they are slow growing initially, they are simply growing beneath the ground where the growth cannot be seen, but where it will provide the important soil stabilizing benefits. [back to top]


Fertilizer

As mentioned under the nutrient loading tolerance section, most native species do not require any traditional fertilization to become established. Fertilizer application promotes the growth of many undesirable weeds and should not be used. Traditional landscaping specifications should be modified to discourage fertilization of native plantings. [back to top]


Depredation

Depredation refers to the problem of wildlife eating the plant material, including root stock, plant shoots, and seeds. Many of the native plant species described in this Guide are an excellent wildlife food source. When a large amount of seeds and root stock are put into an unvegetated area, it is an attractive smorgasbord of food for urban wildlife, especially resident giant Canada geese. Protective measures are required to prevent the loss of native plantings. Installation contractors have a variety of protection methods. Currently, the most successful technique involves cells or compartments of plastic or nylon mesh. The mesh must cover the sides and top of each cell or compartment and be able to prevent animals from getting under the fence. It is very important that these protective measures be monitored and maintained until the plants become fully established (See figures 1 and 2). [back to top]


Naturally Invading Plant Species

There are many species of plants that may volunteer in an area of native vegetation planting. Some of these will present problems, some will not. There may be some species which are desirable natives that have appeared from a soil seed bank or that were blown or carried in from nearby sites. There will be some annual or biennial weeds that colonize recently disturbed soil, but do not persist when the planted material competes with it. Thus these species will drop out and not present any problems. A third group of species that may appear, however, are very aggressive and will overtake planted material without management and intervention. These include such species as reed canary grass (Phalaris arundinacea), common reed (Phragmites australis), buckthorn (Rhamnus cathartica, R. frangula), and purple loosestrife (Lythrum salicaria). These species tend to form monocultures (single species) and do not provide the soil-holding capacity that desired natives provide. These species can be controlled in time with various management tools. Initially, these species may need to be controlled with selective herbicide application. This should be applied in a manner that does not impact other nearby plants and is consistent with the label indications and best management practices. A licensed applicator must be used. Prescribed burning over time will promote the desired native species and reduce many of these non-fire adapted invaders. Mowing can also be used to control some of these species. Techniques used in a given area depend on which problem species are present, setting and context of the area, and preferences and recommendations of the installation contractor. [back to top]


Mowing and Prescribed Fire

Most native plant species are adapted to a natural regime of fire and limited grazing. In a modern urban context, prescribed fire is used as a primary management tool to sustain native plant communities. Prescribed burning requires an Open Burning Permit from the Illinois Environmental Protection Agency (IEPA), permission from the local Fire Department, and a qualified, experienced contractor or crew. Prescribed burning can be done in urban settings in most instances, with proper planning, smoke management, and contingencies. Where burning is not possible, or in the early stages of establishment, mowing can be used as a management tool for native plantings. To reduce weed competition in early stages, native vegetation establishment areas should be mowed once or twice per year with a mower height of 6-12 inches. Normal turf management type mowing is inappropriate and will result in the loss of native plantings. See Appendix B for a list of prescribed burn contractors in northeastern Illinois. [back to top]


Other Considerations

There are many factors that contribute to the success or failure of any given native vegetation planting, just as there are with engineered structures and traditional landscape plantings. This Guide attempts to provide the best available information at the time of publication, but is not an exhaustive reference nor a definitive design manual. Conditions necessary for successful native plant establishment and maintenance vary too greatly from site to site and from year to year to allow absolute guarantees of success. The use of this Guide should, however, substantially increase the likelihood of success and will provide a base of understanding for interpreting results at the project site. Best professional judgment and experience must enter into the design and implementation of any project. Finally, it is important that designs include a maintenance and monitoring plan. In the short-term (3 to 5 years), it should identify performance criteria for the landscape contractor. For example, it should also identify a responsible party for long-term maintenance once the contractor’s job is complete. The long-term maintenance will generally be less costly than traditional landscape maintenance. [back to top]