Join Landscape Consultants HQ for our newsletter with professional landscaping advice. You can opt out at any time.

Design Considerations for Large-Scale Projects

roadside planting plans, adam woodruff, piet oudolf

Design of roadside plantings involves unique challenges. Roadside plantings will never receive any hand weeding or close inspection. Try walking for a distance of at least a mile, and imagine spot treating every weed along your way. Imagine pruning and shaping every shrub, and evaluating and keeping healthy every tree for the entire length of your walk. Imagine doing all those things in ninety-five-degree heat among broken glass and rubbish. Now, imagine doing all this for a distance of several hundred miles!

Professional landscape crews will not agree to maintain rights-of-way in the same manner as they would a commercial or office property. Government agencies will never have a budget which allows such extravagance. When you design a roadside planting, you must consider that maintenance will be, at best, two or three rough mowings with a tractor, a few passes for litter removal, and string trimming around appertances. That’s it.

The designs of Adam Woodruff and Piet Oudolf are amazingly beautiful! It would be interesting to calculate the actual design, installation, and yearly maintenance costs per square foot. Their designs are not simple and not easily scaled to large roadside projects, but roadside designers can learn valuable lessons from their example. The exciting garden results of Woodruff and Oudolf come from integrating different plant species in complex relationships with their compatible neighbors in carefully constructed, imaginative works of art. Reaching for similar results on the rights-of-way is not fool-hardy, in spite of the obvious budget challenges.

Planting plans for roadsides are not as simple as tossing a few wildflower seeds on the bare ground. Establishing a self-sustaining meadow on a roadside is not practical for maintenance reasons more than anything else. Anyone who has ever planted and maintained a roadside wildflower plot can tell you, there is nothing more complex than a simple flower meadow. Using only native plants does not magically erase the need for skilled maintenance. Photograph-worthy results, even if designed to be low maintenance, is much more costly than can be provided by right-of-way project funds.

On roadsides, roadside maintenance crews are busy with bigger issues than aesthetics. There are many dead deer and tire alligators to retrieve and transport to an appropriate dump. The people maintaining the roadsides are unclogging culverts and clearing accident sites. They are fighting back a sea of invasive plants. In the Southeast, the vigorous invasives can grow beyond the woodland edge and eventually into the pavement of the travel lanes. The maintenance crews are not skilled in weed identification. They will never have the time to walk a site and clip back spent blooms, hand-pull Johnson grass sprouts, or water seasonal color.

There are creative things a landscape architect with experience and plant knowledge can do to copy the ideas behind a Woodruff and Oudolf design, even considering the challenges of planting on public rights-of-way. The intricate interplay of atmosphere, art, diversity, and use of seasonal color can be made practical for roadside vegetation planting plans, even with the harsh environment and difficult realities. You just have to push yourself to new levels of plant knowledge and try out your ideas on similar, but smaller projects until you become confident of what will and will not work.

• Protect and preserve the unmanaged woods area beyond the clear zone. Clearing trees from right-of-way fence to right-of-way fence is a costly mistake inexperienced roadside engineers can make. Every square foot of unmanaged woods is a square foot that does not need to be weeded or mowed. The unmanaged woods provides a buffer between travelers and the ticky-tacky clutter that congregates adjacent to the traveled way. The unmanaged woods acts as a fire break for litter and invasives, so they don’t spread beyond the rights-of-way. If your state is one that does not allow billboard companies to remove right-of-way trees, encourage legislators to continue to protect your public trees.

• Think large scale with your planting plans. You need at least five thousand herbaceous perennials to have any visual impact for a planting on the rights-of-way. You will need to use double or triple staggered rows of shrubs to create line and form on the ground plane. Individual small trees are invisible at seventy miles per hour. They need to be massed in groves.

• Use color for visual impact, including fall leaf color, new spring foliage color, berry color, foliage variegation and hues, and bark color. Flowers are great, but flowers are often too small to be noticed by passing cars unless they are massed in the thousands. Your most effective use of color will be with other plant components.

• Groves of trees can be consolidated in plantings closer than ten feet on center to allow leaf litter to self-mulch the understory. A mix of native grasses and forbs can be seeded under the groves, allowing the newly-planted trees to develop a shade canopy.

• Trees will need maintenance every few years. A regularly-scheduled evaluation and clean up by a certified arborist or licensed forester should be a part of any maintenance budget.

• Pollinators can be incorporated into planting plans by using native seed mixes of ornamental grasses and broadleaf herbaceous forbs as the ground cover in areas that are not mowed regularly.

• The woodland edge can be manipulated by foresting and mowing practices to create pleasant, undulating boundaries between the safety clear zone and the unmanaged woods.

• Substantial sweeps of large, colorful native flowering and berry-producing shrubs can be nestled against the woodland boundary in repetitive fashion to add seasonal interest on a bigger scale. Sweeps can be interwoven to provide contrasting color and texture along the woodland edge.

• Avoiding separate islands of plant beds and keeping them nestled against the woodland edge makes it easier for mowing crews to avoid and cause damage to the plant beds. If separate islands are necessary for your design to work, then using the minimum amount of breaks in continuous mowed areas and plenty of space between each island to allow mowing equipment to navigate the space is important.

• Biodiversity can be incorporated into planting plans by varying the species of each grove of trees and shrub mass used in your design.

• Cut down wildflower plots shorty after blooming has finished to avoid too-dense growth and to redistribute dried seed heads to other sites near the woodland edge.

• Plant installation times can be limited to wet, cool months to help new plantings survive the dry, wind-blown sites and establish good root systems.

• Avoid planting shrubs and trees in medians. I know this will not sit well with designers, because medians are the most visible areas of the rights of way and they call out to designers as a blank canvas, ready to be painted. Wildflower plantings, when they are not blooming, which is most of the year, can be messy eyesores in a median. A narrow median is no place for a meadow.

• In urban areas, expensive raised planters set in from the median curbs can be used to elevate colorful plantings and separate traffic, but most medians in most situations are dangerous areas where collisions are common and cross median visibility is essential. Drivers need to be able to anticipate on-coming activity, and tall shrubs obscure the view. Trees in medians act as fixed objects for driver who inevitably will cross into medians by mistake. Medians handle storm drainage, and a down slope to a central median drainage swale is an invitation for errant drivers. Putting a fixed object in the bottom of one of the swales can result in a lawsuit.

• Medians are dangerous places for maintenance crews. The safest way to design a narrow median is to keep it in turf grass or pavement.

• Keep the boundary between woodland and mowed turf clear of invasive plants like Chinese Privet, at the width of a couple of tractor mowing widths into the understory. Woody invasive plants love to encroach into grassed meadow areas where they become too thick to mow. Interstate vegetation maintenance contracts should include provisions to eliminate and chemically treat invasive woody plants smaller than three inches in diameter at the woodland edge, on bridge embankments, and near guardrails to stop their encroachment before they become small trees. This is an expensive addition to a contract, but the annual prevention will save taxpayer dollars long-term. Keeping these areas clear of invasives looks good, protects structures, and prevents signs from being obscured. The cost is justified tenfold.

• Plant proximity to vehicles means you are probably planting in a utility corridor, with all the conflicts that go with it. If you have the space, keep your plantings at least forty feet from the road edge. If you do, your planting will not be run over by errant drivers, any irrigation system will be left intact and not damaged, and the planting will be beyond the ever-present clutter of signs and other things that hang out at the edge.

By scaling up the ideas of garden diversity, artistic flare, and plant knowledge, you can design attractive roadsides that work within the limitations of low-bid maintenance contracts for large-scale roadside plantings. Replacement plants and supplemental water are not possible. Understanding plant material and plant material experience, including growing plants on difficult and challenging sites is essential for success.

By scaling up, changes must be made in a typical, artistic garden naturalization design. Roadside designers must anticipate very little maintenance beyond two or three mowings a year, so their designs must be allowed to grow a bit wild and messy. Huge amounts of plant material must be used to have any visual effect, so the plant choices must be die-hard, reliable species. Scaling up lessons learned from the new garden naturalization style can work, if designs are practical and the plant choices will survive.

Roadside Planting Plans