Order your seeds! Parkseed.com and Burpee.com are the big players. KitchenGardenSeeds.com is both reputable and charming. Johnnyseeds.com gets good recommendations. Heirloom seeds are inspiringly preserved and sold through seedsavers.org.
If you have a Christmas tree, you can cut off the branches and use them to protect your more vulnerable plants. I usually spread mine over my lavender, which may or may not help it survive the winter (I’m hoping). This year we have almost no snow cover so I also piled branches around and over some baby rhododendrons and mountain laurel, to protect them from bitter winds and hungry deer.
Prune your houseplants by pinching back new growth to encourage bushier plants.
Group your houseplants together on a tray filled with pebbles sitting in a bit of water to increase humidity.
Water splashing on the leaves is generally a bad idea because it spreads disease, but if you notice that your plants are dusty, give them a gentle mist or shower with room-temperature water. Don’t wash African violets because they develop water spots on their leaves quite easily.
Protect your houseplants from very cold windowsills by closing the curtains at night.
Gently brush off heavy snow from your bushes and trees to avoid breaking branches.
If you use salt on your driveway or walkway, spread it carefully to avoid getting it on your plants. Consider switching to sand or sawdust.
Check your garden equipment. Repair and sharpen your tools. I know, boring but you’ll be grateful later.
Take stock of fertilizers and insecticides. Go ahead and order what you’ll need for the season.