The nursery industry and the gardening public seem to have an unhealthy fixation on NEW. We can’t wait for the next Knock Out® Rose, or Proven Winners® annual, coralbells, or hosta. I am guilty of this myself, regularly stocking the shelves here with all the latest new plants. But when it comes right down to it, another coralbells isn’t really that different from the 6 or 20 other varieties we already have. Another red maple cultivar isn’t really that different from the dozens already out there. Don’t get me wrong, many of the new cultivars are improvements on existing species (think disease resistance, improved form, or healthier growth characteristics). But new just for the sake of new can get us into trouble.
What we really need to focus on is DIFFERENT. When thinking about community plantings or any large scale planting, the rule for the last 20 years or so has been the 10-20-30 rule, first proposed by Dr. Frank Santamour Jr. of the National Arboretum – Limit plantings to no more than 10% in a single species, 20% in a single genus, and no more than 30% in any single family. This sounds good, but can still get us at 20% ash, or 20% maple. Not good enough when emerald ash borer or Dutch elm disease comes around. Dr. John Ball from South Dakota State University has been promoting what he calls the 5% rule. No more than 5% of any single genus. So 5% maple, 5% oak, 5% Kentucky coffeetree……etc. Talk about diversity!
What does this mean to the average gardener when selecting trees for your own yard or neighborhood? It’s pretty easy. Look around your yard, your neighbor’s yard, down the block – and plant something that you don’t already see. Enjoy the blooms on the crabapple next door, and plant a serviceberry. Marvel at the fall color on the red maple up the block, and plant a tupelo. The important thing is to keep planting trees when they die, or better off, before they die or are cut down. Keep mixing it up, and our grandchildren and their grandchildren will not have to see bare streets where the monoculture of trees has been wiped out by the Dutch elm or emerald ash borer of the next generations.
Dr. Ball’s article is available at http://www.amerinursery.com/american-nurseryman/the-5-percent-rule/
All those trees you’ve never heard of? You already know where you can get those! And the picture you see is me planting a tree with MY grandson!