Make mulch Cut off the boughs and place them on the ground like a blanket to protect plants that are susceptible to windburn, plants that are marginally hardy in your area, and plants that might come up early and be nipped by a late spring frost.
Give it to the birds Move the tree in its stand outdoors for the winter, where it can provide food and shelter for wild birds. Even better, put the tree near a bird feeder or hang bird treats from the tree—like bags of suet or a small piece of wood or thick cardboard smeared with a mix of birdseed and peanut butter—and it will not only attract birds but feed them, too.
Give it to the fish Sink your tree in a pond (with permission, of course). In deep water, old trees become habitats for fish and aquatic insects. In shallow wetlands, trees can act as barriers to sand and soil erosion—though currently only the State of Louisiana has a tree-based restoration project in place.
Compost or chip it Call your municipality’s administrative office to find out if your town has a special day for picking up Christmas trees or a place where you can take them after the holidays where they will be ground into wood chips and/or composted. Often you can go to the municipal compost site in spring and get free compost and/or wood chip mulch for your garden.
Turn it into a trellis Move the tree to a corner of your yard and in the spring set it up in your garden as a trellis for peas or beans.
Plan to plant for next Christmas Think balled-and-burlapped when you purchase next year’s tree and you’ll be able to plant the tree after the holidays.
Source: Organic Gardening