Comfort level and provenance

Each plant has evolved its individual ‘comfort level’.  Some have comfort levels that span all 7 continents, such as Poa annua - Annual Bluegrass. Poa annua is now found on all 7 continents. (
So, if we were to assign Poa annua a comfort range of 1000, I would estimate that most of our desirable garden plants are in the 400-700 range.  Common weeds would be in the 700 to 1000 range. Of course, most of the plants many of us would like to raise in our garden, but cannot, would be in the 200-400 range -- some of us can grow them and others cannot. Those in the 1 to 200 range are typically those that just cannot be raised out-side their native environments.

I am a firm believer in plant growth provenance. All non-hybrid plants, that we grow in our gardens and landscapes, come from plants found in the wild.  Often, plants are selected and introduced from a single location within a plant’s native distribution. Let’s take for example: Quercus alba-White Oak. Its native range is southern Maine through Northwestern Florida to southeastern Texas to almost due north to the Twin Cities and back to Maine. (Native Trees, Shrubs and Vines for Urban and Rural America by Gary L Hightshoe, Van Nostrand and Rheingold 1988, ISBN 0-422-23274-8) Natively, this plant occupies a huge area made up of significantly different ecosystems. Since most white oaks are raised from seeds and not cuttings, would you expect seeds gathered from Northwest Florida and grown in Northwest Florida to be hardy in northwestern Wisconsin? And, conversely, would you expect those from Northwestern Wisconsin to be heat hardy in northwestern Florida?

Our nursery experience has provided us with some interesting answers. A number of years ago we purchased Parrotia persica-Persian Ironwood trees raised in western Oregon state. They all died. When we purchased Parrotia Persia trees raised in the Midwest, they all survived.
When we buy Hydrangea quercifolia – Oakleaf Hydrangea grown from a cuttings raised in the South, while they survive, they rarely flower in our area of Wisconsin. However, if we buy them from growers in north-central Nebraska and/or west Central Maine, they flower beautifully in our area.

We are led to believe that all of those new hybrids of Heuchera are hardy for us in southern Wisconsin.  Our experience shows that many of them cannot tolerate our summer’s high humidity and heat, as well as our winter’s extremely low humidity and cold. Some of these hybrids involve numerous species of Heuchera, ill-suited to our area.

Provenance is not only were the original plan came from, but where the plant is now being raised. Purchasing plants grown in Southern California, or any of the southern states, have never experienced the vagaries of south central Wisconsin. Yet, many garden centers are flooded by plants raised in the southern states and Southern California. They grow bigger and faster in those parts of the country. They can be shipped to our area and sold for less than plants raised in the Midwest. Plants raised in Midwest are culled by our climate. Those that survive, have the genetic makeup to do so. Those that do not, are not sold, as they died before ever making it to the market.

I commonly hear ‘That plant is not hardy here!’ While that may be true for your particular landscape, it may not be true in all landscape environments of our area. I cannot raise Rhododendron in my personal landscape. I live atop a penultimate moraine off University Ave. on the west side of Madison. My soils are 60%+ sand and of a alkaline pH. Even planting them at the downspouts, does not afford them proper growing conditions. However, planting Rhododendron in the landscapes in the Carver Street area in Madison, results in rhododendrons growing to 10+ feet.

So, from my personal experience Rhododendron are absolutely not hardy in Madison. But from my professional experience, many are very hardy and perform beautifully.

So, the next time you go to a nursery or garden center, inquire where the plants are raised. You will then be able to cull those before they make it into your garden.



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