by Ken Muellers
We have all heard the expression “variety is the spice of life.” Well, I propose that for plants in the landscape it is much more than the spice of life – it can be the difference between life and death!
Some of the greatest landscape tragedies begin with ignoring this simple principle of a diverse landscape. Case in point, American elm trees. Planted for their stately beauty, they once graced main streets in almost every town in the East, but this popularity helped lead to their downfall. When Dutch elm disease arrived in the States, the beetles which help spread the fungi that causes the disease found it very easy to jump from one tree to the next, until almost every elm was dead. The great quantity of elms, and their proximity to each other, provided an opportunity for the disease to spread easily.
Lesson not learned. A few decades later, after rows and rows of Canadian hemlocks are planted for privacy screening throughout suburbia, a little insect called Hemlock wooly adelgid made an appearance on the scene and quickly went from plant to plant (after all, we were kind enough to line them up for them) devastating millions of hemlocks.
Lesson still not learned. Now we are facing potential mass loss of ash trees from Emerald ash borer. Ashes, which are widely planted as a street tree throughout the mid-west, are easy pickings for this pest. At the same time, Oak wilt is threatening our oaks and Asian longhorn beetles are a potential disaster for our maples.
In all these situations, the practice of mono-culture (planting all the same thing) has already, or may lead to, devastation from pests and disease. Most plant pathogens are specific to a particular genus (oak, maple, pine, etc.) and many are specific to a particular species of that genus (red oak, pin oak, swamp oak, etc.). By planting different species, we can all do our part in preventing the next plant pandemic. Just as any investment advisor will recommend a diverse portfolio to prevent heavy losses, a good horticulturalist knows that a diverse landscape will help prevent disaster.
This varied landscape also has other advantages over mono-culture. You will also attract more diverse wildlife. With plants providing a variety of different flowers, seeds and berries at different times of the year, birds and other critters will have more opportunities for food and habitat. Another reason is aesthetics. A diverse landscape will provide a more natural appearance. Having a mixed border planting with groups of a few evergreens interspersed with flowering trees and shrubs will provide a much more attractive view than a single row of some overplanted evergreen (can you say Leyland cypress?). If you do need a screen of all evergreens, try to use small groupings of different types. Not only will it give you varied textures, colors and sizes, it will lessen the potential for disaster from insects or disease.
There are so many unique, beautiful plants, it is a shame that the same few plants are used over and over. So, next time you are looking to plant something new, try to break out of the rut and choose diversity.