NOT YET

     That is my answer to clients who have been calling to ask about putting mulch down for the winter. It is still good planting weather out there. We can't even plant bulbs for another month because it is too warm -- and it is supposed to hit 80 one day next week. So let us not be in too big a hurry to welcome winter back.

     Many people put down mulch way too early because they don't really understand what it does. It's job is not to keep plants warm like a sweater. Rather its main job is to keep the temperature around plant roots from fluctuating wildly.

     Most of us in Chicago are aware of the lake's effect on temperature. Since the denser water changes temperature more slowly than the air, the shore area tends to stay cooler during the day and warmer at night. Similarly, lake shore temperatures tend to be cooler during spring and summer and warmer during fall and winter.

     The land acts the same way. It changes temperature more slowly than the air above it, and the deeper down you go the less affected it is by air temperature.

     By adding an extra layer on top, your mulch is in effect pushing your plant roots further down and making them less subject, not so much to cold weather per se, but to the variations in temperature that those of us above ground love so much.  Those variations may include a -30 degree cold snap that lasts a day or two. But they also include those January thaw days, and the cycles of freezing and thawing that cause frost heave in our plants and even kill them.

     Plants respond to the shorter days and lower temperatures of fall by beginning to shut more and more processes down and going dormant. When we put down mulch too early, we are fooling our plants into staying active longer than they should. So lets not get into too big a rush. Let your plants go through several hard freezes when your thermometer breaks 20 degrees before you reach for the mulching shovel.