Permission and Preparation
If you would like to install a roadside planting on public land, such as on the shoulder of a freeway or near a rest stop, you must first get permission from your local government. There may be rules about not growing woody plants like trees or shrubs, and there may be regulations regarding plant height or what types of flowers and grasses may be planted. The government may even prefer to just keep mowing the roadside. Even if you own the land yourself, there may still be rules about how close the roadside you may plant trees or shrubs. After you've gotten the green light from the highway department, prepare your roadside site by removing any garbage, pulling up any noxious weeds, smothering or tilling up the turf grass (if necessary) and applying a heavy layer of organic compost. Be prepared to water your roadside planting occasionally throughout the first growing season, until the plants become established; deep, infrequent watering is best, because it encourages the roots to dig deep into the soil.
Roadsides are often dirty, smelly places, but roadside plantings can help clean them up. However, you must choose strong plants that can tolerate motor oil, road salt and car exhaust. Tough, pollution-tolerant trees and shrubs include serviceberry, eastern red cedar, white oak, crabapple, honey locust, dogwood and sumac. For flowers and grasses, consider daylilies, artemisia, bluestem and hostas. Consult your local agriculture extension office for specific recommendations for your area.
The impermeable surface of highways can create a lot of runoff, washing away topsoil and allowing pollutants to seep into the watershed. The root systems of plants help hold the soil in place and also help filter out chemicals. Choose plants with deep, robust root systems. If your local highway department won't let you plant trees or shrubs, ask if you can plant a low-growing forb. Native wildflowers generally have deeper roots and provide better erosion control than introduced or cultivated species. Most roadside sites will do best with plants that are drought tolerant, such as lupine, while drainage ditches will benefit from marsh plants such as cattails.
Although many people like planting gardens to attract wildlife to their yards, a roadside setting is not the best place for it. Plant thick shrubs and tall grasses far away from the roadside so that deer and other animals trying to cross the road will be more visible by drivers before the animals leap out into traffic. Avoid planting fruit trees that could attract animals next to heavily trafficked roads. On quiet country roads with little traffic, or in urban setting with little wildlife, this may be less of a issue.