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Roadside Use of Native Plants

Specifying A Native Planting Plan — Specifications from Experience

Bonnie L. Harper-Lore, Federal Highway Administration

Learn as much as you can from your region's woodlands, grasslands, and wetlands. The vegetation of your State has sorted itself over the landscape in successful associations that match the environmental conditions including climate, geology, and hydrology. The best way to learn, in addition to the references listed, is to hike through examples of plant communities protected as preserves by the Natural Heritage Program and The Nature Conservancy. With a visual image and the knowledge of species composition of these remnants, you can better make decisions about the projects that run through similar community types.

To achieve a semblance of a grassland or other community on roadside rights- of- way, begin with a designs described by Morrison. Write a detailed specification and supervise the installation. Here are some tips to consider:

TIMING is everything in native plant seedings. Because of climate differences, good timing differs across the country. Beware of synchronizing your planting calendar with that of local cool- season crops. Many native grasses and forbs are warm- season species and need to be planted later. Obviously construction contracts are not always flexible enough to accommodate perfect timing. Planting a temporary noninvasive erosion control would be ideal, but most contracts cannot do this. On top of that constraint, some regions are learning that success comes with fall rather than spring plantings of native seed. There is strong evidence that native grass and forb seeds will lie dormant in the soil until climate conditions are appropriate for germination. Bottom line, many seasoned native grass contractors have successfully widened the window of planting opportunity ... proving once more that we have a lot to learn. Landscape contracts let separately from general contracts would improve establishment and save money over time. Ultimately it is the timing of the natural weather patterns that will make or break the planting. Low precipitation, flooding or drought episodes are unforeseeable.

SITE PREPARATION is key to successful establishment. Analyze existing vegetation, adjacent vegetation and soils to define weed problems that could compromise your project. Control as much as possible. Disturb existing soils minimally. Derive a plan for weed follow up.

SEEDING RATES are often too high for the project, wasting precious seed, and budget. Of course the per/acre or hectare rate will vary with equipment used. Higher rates are needed when broadcasting or hydroseeding. Drill seeding is a more efficient delivery system, but tractor-drawn drills cannot be used on steep slopes.

To define a successful seeding rate, it is wise to know the species well. A pound of switch grass contains a lot more seed than a pound of Indian grass. Consequently it is an easy species to accidentally overplant. Understanding pure live seed is important to get what you pay for.

Rates for native wildflower seed is usually low at 2- 5 pounds/acre. This rate is low for a number of reasons:

  1. lack of availability,
  2. high cost per pound, and
  3. natural wildflowers exist as accents in grasslands.

Rates for associated native grass seed is higher at 7–10 pounds/acre. This rate is higher because:

  1. native grass seed is more readily available,
  2. it is less expensive, and
  3. native grasses are the main component of a grassland.

PLANTING METHODS vary across the country. Although hydroseeding is preferred by some, accounts exist of expensive native seed being caught up in the slurry and never reaching the soil. Specialized seeding drills that handle a variety of seed shapes, sizes and pubescence have been successful. They can plant on new construction sites or interseed on established slopes. Specialized broadcasting equipment is better applied to prepared soils. Broadcasting leaves no unnatural rows behind. Some success has occurred with the use of fertilizer spreaders. This kind of broadcasting cannot be calibrated. Planting seed as seedlings is done when equipment cannot be used on steep slopes or when a high visibility planting needs enhancement. Learn what works in your region. Be creative and plan ahead.

FOLLOW- UP is critical to the success of these plantings. Contrary to the idea of no maintenance plantings, some follow- up is necessary. For example, if normal precipitation does not follow, supplemental waterings might be necessary until the seeding is established. Then, if you have matched the species to the site conditions, the plants are on their own. Ideally, there is no need for irrigation systems in native plantings. Remember to build maintenance into the contract when possible.

Also important in new plantings is the need of weed control. Whenever the soil is disturbed or bare-grounded, nature will fill in the spaces with pioneer plants. Many opportunistic pioneers are considered weeds that threaten the planting. Spot spray noxious weeds where necessary. Pioneer weeds should be mowed off to avoid their shading out or out-competing the planted seed. Remember to mow high enough so that desirable seedlings are not affected. As for long term maintenance, prescribed burns where appropriate, annual mowings, and/or spot sprayings will be necessary.

These mowings will give the project a cared for look allowing you some time before public expectations are met. When seeding perennial plants, establishment will take a number of years. Often signing such a planting, can help explain the patience needed. A local newspaper feature can be helpful for public awareness.

SPECIFICATION TIPS are useful since we still operate in a low-bid world for the most part. We must specify all the details of these not-so-common plantings. Many winning contractors have no experience with native plantings. Common mistakes include: I) not ordering these uncommon seeds and plants early, 2) not demanding local origin seed or seedlings, 3) using a conventional grass drill and planting too deeply, 4) making up time on a project and skipping steps in weed control, 5) working with untrained inspectors. NOTE: Specification writing tips are included in the Appendix.

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Questions and feedback should be directed to Deirdre Remley (deirdre.remley@dot.gov, 202-366-0524).

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