Good question! Wind chill only affects people or rather the way we perceive the temperature. Plants are only affected by the actual air temperature which is what the USDA Zone Plant Hardiness map takes in to account. The real issue with winter winds on plants is that it can dry them out. This is one reason it's important to make sure your plants (esp. evergreens) are well watered heading in to winter.

I agree....wind chill does not effect plants.

When I garden with certain plants that may not be winter hardy to my zone, I plant in what I refer to as a "micro-climate". Meaning the plant has protection on 3 sides. Example....the house, a large fountain grass, and the garage blocks the harshest of winter cold. The large fountain grass and buildings act as a barrier.

If interested, do a search on micro-climates. I'm sure they'll explain it better.

Many of my plants are also covered in mulch/leaves which protects them. I let the leaves fall in the fall on my flower beds and don't clean them out until spring. It's similar to the above post. My plants on the south-faced slope get more sun and less wind than the ones on flat ground in open spaces (where the leaves won't stay and get blown away). Heidi in Nebraska