December is a light duty month, (finally!) with a few opportunities to get ahead of the game for spring.
It is a good time to test your soil. There is adequate time to amend for pH before the growing season, and to be able to prepare for any missing nutrients that you can add just before spring. December is also a great time to do dormant season pruning. There are also many ways to help birds over-winter without creating a rodent problem.
All of this and more is available in the December Tasks in the Garden and Landscape article.