We just returned from an intense two-week road trip to the Great Lakes. We visited thirteen states and one province and saw at least a glimpse of all five Great Lakes. You can see our route at right. It was a great trip. We took lots of photos, plus our drive across the prairies of North Dakota means that I’ve finally checked off my bucket list goal of visiting all 50 states!
Michigan was my 48th state. We spent a lot of time there visiting friends, looking for birds, and admiring the blue lakes and endless hardwood forests. Avoiding the interstate as much as possible, we passed through dozens of small towns full of clapboard houses. I was entranced by their emerald green lawns and tidy shrub borders and flower beds full of plants I never see here along the Front Range. Yet, Michigan lies in the same USDA zones as Colorado—primarily zones 4 through 6. I was puzzled—why can Michigan gardeners grow so many plants I can’t? Clearly, the minimum temperatures that define the USDA’s zone maps are just part of the equation. What other factors determine what plants flourish, and which struggle and die?
It’s immediately obvious that Michigan and Colorado have vastly different climates, even though our temperatures are similar. All that lush vegetation is so different from our evergreen forests or open prairies. It turns out that most parts of the state get at least double the rainfall that Colorado Springs gets—30 to 40 inches per year, as opposed to about 16. All that rain raises the humidity, allowing shrubs and trees with wide, thin leaves to thrive. Additionally, it’s more uniformly distributed throughout the year. As we drove north, we constantly commented on the huge, perfect lawns, with nary a sprinkler head in sight. In winter, the constant snow cover insulates the ground, protecting roots from the intense cold above ground.
I suspect this is why hydrangeas and hostas are so popular—every garden seems to have them. I’m jealous. Yes, we can grow them in Colorado, as long as we fuss over them—I am successfully nourishing a lovely hosta in a big pot on my sheltered front porch—but the edges of their leaves tend to brown in Colorado’s dry air. They also demand more water than I’m willing to pay for. And then there’s hail. Plummeting hailstones shred those delicate leaves and, especially in the case of hostas, the leaves are the reason we grow them in the first place.
Related to temperature, but often overlooked, is how quickly temperatures change from day to day. Colorado’s low humidity and location far from large bodies of water mean that we experience dramatic swings from hot to cold and back, often in a single day. I’ll never forget a lovely morning in late May, a number of years ago. I was happily enjoying the 70-degree day as I set out my tomato and pepper transplants. By mid-afternoon, I was hastily pulling up my tender seedlings and stuffing them back into their pots as a snowstorm sent temperatures plunging into the low 20s! More recently, an unusually warm fall ended abruptly in November as overnight temperatures—which had been in the 40s—nose-dived into the low teens, coating still-green leaves with rime ice. I lost several well-established, otherwise-hardy plants that year, as they just couldn’t handle the sudden change.
Michigan, on the other hand, has more stable temperatures. Sure, they experience cold snaps or heat waves, but these are mitigated by Lake Huron on the east, Lake Michigan on the west, and Lake Superior north of the Upper Peninsula.
Another consideration is soil. Because of its more abundant precipitation, Michigan gardeners can grow blueberries, hardy azaleas, and holly, all acid-loving plants. The gigantic maples we saw showed no signs of chlorosis, a problem in Colorado because our alkaline soil locks up iron, making it unavailable to roots.
Looking at those lush gardens, I often got the impression that all a Midwest gardener has to do is throw some seeds in the ground and stand back. It wasn’t until I struck up a conversation with a local that I realized that all is not roses. Michigan harbors more pests than Colorado—a lot more. There are all sorts of nasty beetles and other insects that love to munch on stems, leaves, and flowers. There are fungal diseases galore. And then there are weeds. All that lovely top soil and rainfall, coupled with warm summers, means that gardeners are constantly battling a jungle of unwanted plants.
After some reflection, I think I’m glad I garden in Colorado.
Mountain Plover 
As you’ve mentioned beetles, we in the Denver/Englewood area have been invaded by the worst pest of all, courtesy of a local golf course. I’m referring to Japanese Beetles; voracious, nasty, wily and nothing seems to eat them. Unlike the East Coast and Midwest, the birds around here don’t notice them as adults or larvae, so they reproduce unabated. Only the strong insecticides will kill them, but that also puts beneficial insects at risk.
So at our house we’re down to hand-to-hand combat with a pail of soapy water, starting in early morning and from time to time throughout the day if we can manage it. We have also eliminated their favorite habitat, Virginia Creeper and are urging our neighbors to do the same, with mixed results.
Our poor roses take a real beating from mid Summer to early Fall. And starting last year, they’ve developed a taste for other plants as well.
I feel so badly for those of you who garden in Denver. I’ve notice the devastation at Hudson Gardens, especially on the dahlias. I was curious why the Botanic Gardens aren’t in equally bad shape, although I’ve seen some there as well. I can only assume they are either spraying or using their volunteers to keep things under control.
So far, Colorado Springs seems to be either too high or too cold–or they just haven’t arrived yet. I haven’t had a single Japanese Beetle.