One of the main reasons you'd mulch in fall or early winter would be to protect the plants from the cold; more importantly, during the alternating of freezing and thawing temperatures. If plants or bulbs freeze and then thaw, not only can the roots get damaged, but the bulbs and the plants themselves can get heaved from the ground. They're then further exposed to temperature extremes and can't get the protection and moisture they need from the soil.

Recent Northern Illinois, Northwest Indiana, and Southern Wisconsin winters have been brutally cold. We have seen plant and tree loss in the thousands due to the conditions and landscape practices in both urban and suburban regions. Applying an insulation of mulch can have a dramatic effect on the survival of our beloved landscapes.

INSULATION

Cold-weather mulching protects perennials in much the same way as a heavy blanket of snow insulates the ground in winter.

SOIL TEMPERATURE

The effect mulching has on soil temperatures is probably one of the most often overlooked benefits. Many of us are more concerned with above ground temperatures and don't spend much time pondering what's happening underground. Simply stated: Mulch is insulation. It keeps the soil around your plants' roots cooler on warm days and warmer on cold nights. This is especially important during rapid temperature shifts

SOIL MOISTURE RETENTION

Mulch's ability to conserve soil moisture has long been documented. While authorities and test results differ, it is clear that moisture evaporation from soil covered with mulch is reduced anywhere from 10 to 50 percent. Whichever you accept, the water-conserving value of mulching can't be overemphasized, especially in these times of water restrictions and shortages. Root zones require moisture even during the winter to prevent freeze drying of roots.