What should I be doing now in my garden to prepare for winter?

Q: No matter what the time of year, the garden always seems to need attention.  What should I focus on now that the leaves are about to fall? For instance, is it a good idea to prune plants now?  What about those bald spots in my lawn?  Which perennials should be divided in autumn and which in spring? How can I prevent winter damage to evergreen foliage?

First, the best task you can do to prepare for winter is to make sure you have cleaned up dead and diseased debris from your garden beds. Most diseases and pests are able to over-winter in the soil. By ridding your beds of any leaf litter, you will reduce the chances that pathogens and pests will remain in your garden. 

Weeding is the second most important task to do right now. Any weeds that are flowering now are putting out seeds that will become next year’s weeds. Moreover, dandelions, bittercress, and garlic mustard are all growing now, getting ready to bloom in early spring. Try to get ahead of the cycle by pulling as much as you can now! 
Once the ground has completely frozen (here in CT, we’re talking December), you are welcome to put down a thin layer of mulch. You don’t want to create an under the mulch highway for voles and mice to gnaw at the plant roots, but an inch of mulch will prevent frost heaves by keeping the soil at a constant temperature. 
Second, my very generalized pruning rule is: prune plants after they’ve flowered. The other problem with pruning now is you will be stimulating new plant growth that will not be winter hardy (so you’ll be pruning again this spring to cut out all the dead and stressed branches). There are a few exceptions that you can do now, if desired, if you are willing to forego next year’s blooms. Forsythia is a good example. Anything that is completely dormant can also be pruned, but nothing is completely dormant until well into December. Finally, one can prune out any dead, diseased or distressed branches at any time of the year. 
Third, there are multiple issues with bald spots in turf. Do you have a grub problem? If so, over-seeding will only be decimated by those pests next year. If it was an area where you pulled weeds, this is a great time to over-seed. Was the patch in an area that was over/under watered? Was there disease? You need to get to the ‘root’ of the problem and then find solutions. 
Fourth, most perennials do well being divided in the autumn. They are going into dormancy and, as long as you give them care until a hard frost, they will thrive next spring. 
Finally, to prevent winter damage on evergreens, you need to focus on two practices. First NO pruning after late summer. As mentioned above, pruning stimulates growth. When an evergreen shrub is pruned in the fall, the new growth doesn’t have time to become winter hardy and will be come distressed, or die. Secondly, if your evergreens are in an exposed, windy area, you may want to consider spraying them with an anti-dessicant or even wrapping them with burlap.