Line, color, shape, texture, and form establish the bones of your landscape. For roadsides, the lines need to be well-defined, with double or triple rows of plant material. A single row might work on a pedestrian scale, but not on an interstate. For trees, it helps to plant a double, staggered row of trees about ten feet apart. For tall shrubs, a triple row will look best. For low shrubs, five or more staggered rows will be needed to make significant delineation.
Shapes need to be kept simple. Drivers don’t have time to register a visual image of complex shapes. And, this is important— a beautiful pattern on a landscape drawing plan sheet may not register at all to people in passing cars. Don’t design for birds! Design from the perspective of someone seated with their eye level at about three feet above ground on the pavement. A delicate S-curve will only be effective if the ground beside the road is sloping uphill. For steep down slopes, very little landscaping may be required, so you can concentrate more money and material in other places.
You can find more information about trees in The Advanced Guide to Roadside Design: How to Create Successful Public Landscape Projects, part of The Advanced Guide series.
Texture is the design element that provides the most visual excitement for travelers, especially since the woody plant material that survives well on roadsides has only fleeting moments of color. A strong contrast of coarse foliage against fine-textured leaves is a great look!
The form and natural habit of plant material can vary quite a bit. Try to provide interest by using spiked shapes with mounded shapes and weeping shapes with low, flat ground cover. Use a delicate hand with contrasting forms in your landscape design, just as you would in adding spices while cooking a soup. Think through each variation carefully.
Plan on using the natural shapes of mature versions of the plants you choose for your roadside design. Expect to go through periods when no pruning takes place during fluctuations in the economy. And, if you want to maintain the natural growth of the plants you specify, write a strong prohibition in the maintenance specs for any use of shears. There are lots of landscape crews out there that would love to show off their topiary skills! An enthusiastic maintenance crew can reshape your elegant design into a joke in a single day. Make sure they are fined heavily if they attempt to use shears on your roadside landscape plants, at least in the first few years of growth as shrubs grow together into a mass. Remind your landscape contractor again and again to stay away from your shrubs with shears.
Most importantly, be bold and strong when incorporating design elements into your roadside landscape plan.