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Posted on Thu, Jan 13, 2011 : 9:21 a.m.

Garden Faerie: How climate change will affect our gardens

By Monica Milla


Despite the increase in average temperatures in Michigan, we won't be growing palm trees any time soon.

Photo copyright Majestic Palm Trees

At Monday's meeting of the Chelsea Area Garden Club, Tony Reznicek, curator of the University of Michigan Herbariam, presented "How Will Climate Change Affect Michigan's Gardens and Natural Heritage?" Even though mean temperatures are rising, we won't be growing palms or figs any time soon in Michigan. It's not about average temperatures, but about extremes.

The talk was highly informative. Even though I took copious notes, I can't possibly do each point justice (plus, I'm neither a PhD botanist nor an atmospheric scientist), so I'll simply share what I found most fascinating.

Firstly, I was intrigued by an overview of 16,000 years of plants in Michigan (since the last glacier retreated). After the melt, Michigan was essentially a gravel pit with rocky, moist soil high in minerals. Slowly ground vegetation grew and then birches and alders appeared. Soil was still gravelly and calcareous. Over time, Jack and red pines appeared. Then the northern mixed forest grew, and finally the southern deciduous forest. In the 1800s, settlers started coming and cleared a lot of the forests for farming.

Settlers also brought seeds from Europe. In 1700, before settlement, there were 1,850 species of plants in Michigan. Remember, it took those 1,850 plants 16,000 years to evolve. Today, there are 2,821 species of plants in Michigan, or nearly 1,000 more in just 300 years. Humans accelerate the rate of change.

Temperature has been increasing slowly over time on its own. Our current average temperatures are 7 degrees celcius warmer than 100,000 years ago during the Ice Age. But again, humans have accelerated that rate of change. Temperatures are 4-6 degrees C warmer today than than they were only 60 years ago.

The rate of change is accelerating due to increased levels of carbon dioxide (CO2), a greenhouse gas that lets light into our atmosphere but doesn't let the heat get back out. Average temperatures are slowly rising around the world. Spring comes earlier, the extent and length of ice cover on the Great Lakes is shorter, and extreme rainfalls may be becoming more frequent.

However, temperatures are means, and some parts of the earth may still get colder, not warmer. Also, a warming earth has more energy which can create unpredictable weather. When the rate of change is more rapid, the extremes are more extreme as well.

By 2095, Michigan will be as warm as the Ozarks are now in summer and as warm as southern Ohio is now in winter. We may think warmer average temperatures mean we can start growing more perennials with lower cold tolerances. For example, the palm Trachycarpus fortunei can survive short spells of temperatures as low as -9 degrees Fahrenheit, and Michigan's average winter temperature is 17 degrees F. But we don't plant these palms now, and we won't in the future, because we get, and will likely continue to get, several days well below -9 degrees. It's not about average temperatures, but the extremes of actual lows and highs.

Warming isn't only about temperature, it's about lack of water. Without ice cover, lakes will evaporate more quickly and plants will require more watering.

Plants with lower heat tolerances will move northward. For example, trembling aspen Populus tremuloides will move farther north, whereas sugar maple (Acer saccharum) will remain.

Plants need CO2 to live, but increased levels of CO2 act like fertilizer. Heat-tolerant plants, like weeds and invasives (poison ivy comes to mind), will flourish with this extra CO2; they will grow bigger, reproduce more, and out-compete other plants. Plants with lower heat or sun tolerance, as well as those that require moist or poor soil (such as trillium an other spring wildflowers) will respond negatively to fertilizer. They do not need extra fertilizer and, in fact, find it harmful, like overdoing on sugar. They could weaken or die out altogether.

So, overall, increased average temperatures over time will mean:

  • A slow shift north of more less heat-tolerant plants

  • An increase in weeds, native and non-native, including poison ivy

  • A reduction of plant diversity

  • Lowering of lake levels

  • Longer and more severe droughts

Tony recommended the following common-sense steps for dealing with these issues (now and in the future):

  • Reduce your own greenhouse gas emissions

  • Mulch heavily

  • Capture, store, and use rain water

  • Reduce the amount of lawn

  • Use more low-water plants

I admit I felt pleased that I've been doing all those things for a very long time. And tickled that instead of thinking of myself as cheap and lazy, I can now view myself as green and low-impact/energy-efficient!

The Chelsea Area Garden Club meets at noon on the second Monday of the month at the Chelsea First United Methodist Church. For more information, contact The Evening Primrose Garden Club meets at 7 p.m. the second Wednesday of the month at the Chelsea Railroad Depot. For more information, contact Both clubs feature educational programs, garden trips, plant sales, plant exchanges, community beautification projects, and master gardener scholarships.

Monica Milla, the Garden Faerie, is a master gardener volunteer, garden speaker, garden coach and author of "Fun with Winter Seed Sowing."



Mon, Jan 24, 2011 : 2:34 a.m.

Ms. Milla - With all due respect, it might be best to stay with the gardening theme. Anthropogenic global warming, aka 'climate change' is a fairy tale; a scam. There is a bright side: all plants enjoy any additional CO2. Think green...


Fri, Jan 14, 2011 : 2:08 p.m.

By 2095 you should have your garden cleared of all that buckhorn, right?

Rork Kuick

Fri, Jan 14, 2011 : 10:17 a.m.

I've lived here since 1975 and mostly noticed that minimum temperatures in the cold season have increased. I've not heard that the summers are warmer, and am skeptical about heat-tolerance being as key as the lack of super-cold days. I worry about stuff like garlic mustard not experiencing enough winter-kill, not poison ivy. I can't find a place to download good data. Between 5000 and 7000 years ago our area used to be warmer than now (mid-Holocene warm period), and the plants weren't quite the same as now.

Monica Milla

Fri, Jan 14, 2011 : 8:52 a.m.

This is a BLOG, not a news article, and it's about GARDENING. Comments are a forum for gardeners, not a platform for political rants.

gerald brennan

Fri, Jan 14, 2011 : 6:05 a.m.

The author complains about the discussion veering off-topic. The entire nature of the article presumes that the "global warming is real and you need to prepare for the consequences!" nonsense is actually a scientific consensus view, which of course it is not. This is useless journalism at its presumptuous worst.


Thu, Jan 13, 2011 : 11:20 p.m.

Jen, The article presumes global warming as a fact (not an opinion). Thus the article itself has created the subject matter for discussion.


Thu, Jan 13, 2011 : 1:35 p.m.

Wow, now we can even explain colder winters with global warming. But what is this about giant poison ivy plants? I thought Apes were supposed to rule the planet in the future.


Thu, Jan 13, 2011 : 1:17 p.m.

Not buying or selling.. The Chinese are the single biggest CO2 producer. The Indians will soon follow. They are trying to pull their people across the poverty line. I do business in both places, the govt. may give lip service to CO2 regs, but they have no intention of stopping growth or spending money on expensive energy to limit CO2... never going to happen. China burns more coal than any other country (yes they have set up some windfarms) and I don't see that changing.

Top Cat

Thu, Jan 13, 2011 : 1 p.m.

"By 2095, Michigan will be as warm as the Ozarks are now in summer and as warm as southern Ohio is now in winter." Please note this on your calendar. Along with the fact that by 1957, we will run out of oil.


Thu, Jan 13, 2011 : 12:54 p.m.

It was only in the 1970s when scientists said we're headed back to the ice ages! Now, only 40 yrs later, theyre saying were getting warmer because of greenhouse gases. The earths temperatures have naturally increased and decreased since the start of the earths temperature documentation. The "experts" are saying the increase of less than 1 degree over a 20 plus year period is causing glaciers to melt and polar bears are at risk of extinction? From less than ONE DEGREE??? WOW! So these glaciers must have kept a continued temperature of 32 degrees since the drop of 1 degree is causing them to melt. Impossible! When the nonsense of global warming began and the federal funding of these radical left, special interest groups started, "global warming" was never spoken of anymore. It changed to "climate change" in case the earth cools back down less than 1 degree in the years to come which it will. We hear nothing about the BIG HOLE in the ozone layer, swine flu, sars, aids, and Y2K the media, special interst groups, and/or the government has used in recent years to scare everyone into believing we are all doomed, for the profit of "non-profits" and the waste of tax payers money funding bogus organizations. Global warming(climate change) is nothing more than a hoax and a waste of taxpayers money!

Atticus F.

Thu, Jan 13, 2011 : 12:37 p.m.

There is evidence to contradict alot of whats been said in this article. I simply think evidence that does not support global warming is often overlooked. And the reason; Are you going to tune in to watch a news channel that says "everything is ok", or are you going to tune into a news station that says "the end of the world is upon us"? Stop scaring children!

Eric S

Thu, Jan 13, 2011 : 11:26 a.m.

The article emphasizes mentions poison ivy multiple times. Just to be clear, poison ivy is native to Michigan. There's a lot more of it here than there would be without people, and it loves CO2, and it counts as a noxious weed because of the human problems it causes, but it isn't introduced.


Thu, Jan 13, 2011 : 10:47 a.m.

I have a plot of land that I was raising varietal grapevines on... Had a bit of trouble with the Chambourcin and some other hybrids because of the winterkill. The Frontenac, Baco Noir, and Marechal foch did ok. I am hoping to grown some Vinifera vines, so I am all in for a bit of warming in Michigan.