Last weekend we had frost warnings. Today we might flirt with 90 degrees. That's spring in Chicago for you.
The distinguishing characteristic of Chicago weather is not that summers are so hot or that winters are so cold or that we get a lot of snow. Any of those things might happen, or not. Our climate is characterized above all by extremes and extreme variability. We share the "continental climate" of the Great Plains--meaning we are far from the moderating influence of an ocean current, so storms and winds and battles between high pressure and low pressure have nothing to tell them to keep it down. They can let 'er rip.
We have the added complications of Lake Michigan and the Great Lakes, which are a heat sink (in winter) and a cold sink (in summer) that creates a barrier to weather moving from west to east. Cool air coming from Iowa crashes into a reservoir of warmer air over the lake, and a noisy disagreement ensues. Or vice versa.
And because the Chicago area is so large it is remarkably varied, with the narrowest range of possibilities near Lake Michigan and a much more exposed and rigorous climate 20 or 30 miles away. There can be almost a month's difference between the last average frost date near the lake--as early as late April--and the average last frost date out in the far western or northwestern suburbs. And even within those numbers is a lot of variation: "average frost date" is just an average, and like all averages it can conceal some funky numbers. One year's very late or very early frost can skew the average quite a bit.
And that's not to mention every garden's microclimates. A spot at the foot of a slope is less exposed to wind that one at the top. A balcony on the east side of a building is more protected from the prevailing wind than one on the west. My narrow garden, on the north side of a 4-story building with a 2-story building and a fence on the south side, gets hardly any sun but is very sheltered. The narrow bed out by the garbage cans, on the other hand, gets lots of sun but dries out much faster.
What does this all mean for gardeners? Four big things:
1. Know your garden. Watch it. Pay attention to where the wind comes from, how fast soil dries out, how the sun moves, where the shadows fall. Pay attention to weather readings from as close to your garden as possible -- the O'Hare temperature means less to me, for instance, than the Midway temperature, and the lakefront temperature means very little.
2. Mulch. Apart from its many other virtues--adding organic matter to the soil, discouraging weeds--an organic mulch is a great protector and insulator, and does much to smooth out the jagged variations of Chicago weather. It holds in moisture against drying winds and insulates the soil against temperature swings. It will help plants stay dormant in spring when the weather gods mischievously pop a 60-degree day in winter between bone-chilling freezes and will keep soil cooler in August when it feels like it's still above 90 at midnight.
3. Choose native plants as much as possible. One of the things that Midwestern natives are adapted to is crazy weather. They have learned over 10,000 years of evolution not to take a January thaw seriously and to grow long, deep roots that can survive an August drought. You don't have to be a purist about this, but expect to have to fuss more over many non-native plants than over most natives, and expect to lose more of them.
4. Keep a long memory. Most people don't remember much past last winter or last summer, so they are always shocked when it's "colder than normal" or "hotter than normal." But around here the only thing that is normal is wild fluctuation, from week to week and from year to year. To be a Chicago gardener is to keep your knees loose and your mind open and to expect anything. And remember: Any time a plant dies, it's a chance to try something new.
Got a garden question? I recommend you call or e-mail the Plant Clinic of The Morton Arboretum in Lisle, the Master Gardeners of the University of Illinois Extension or the Plant Information Service of the Chicago Botanic Garden in Glencoe.
All contents of this post are copyright Beth Botts. Feel free to link or share a brief excerpt with a link, but please do not reproduce photos or any other part of this blog without my express permission.