Q.How do I prepare a dogwood for winter?
I live in northern Michigan. We get snow and below zero F. temps. How do I prepare my little tree for winter? We planted it in May.

Dogwood Trees are hardy in zones 5 thru 9.
Depending on how far North you are you may be down into the zone 4 range.
Even in zones 5 the Dogwood Trees can have trouble surviving the cold.
You can try mulching and adding some protection to the tree with straw bales, but your tree may not survive.
Here are some links for you.
https://www.gardeningknowhow.com/ornamental/trees/dogwood/caring-dogwood-trees.htm
http://extension.illinois.edu/treeselector/detail_plant.cfm?PlantID=592
https://www.gardeningknowhow.com/planting-zones/michigan-planting-zones.htm