When a Christmas tree ends up in a landfill it decomposes and produces methane, a potent greenhouse gas.
Methane's bad news for our climate. But here's the good news -- instead of sending your old tree to the local dump, there are more sustainable ways to dispose of it now that Christmas is over.
Throughout the week, Greenpeace members have been sharing tips and ideas on what they're planning to do with old trees. Here are some of our favourites, sent in via Facebook and Twitter.
1. Re-plant it in a pot
Many Christmas trees, like Norwegian Spruce and Fraser Fir, are surprisingly resilient. And it turns out that, even if the branches on yours are starting to droop, trees can recover if they're planted in a pot of soil and left outside for nature to take course.
As Aimee, a Greenpeace supporter, explained on Facebook: "My parents stuck theirs in a pot of soil last year as an experiment and because they enjoy watching the birds playing in it. However, it somehow managed to root itself and start growing again. They used it again this year and plan on continuing the tradition for as long as possible."
2. Arrange for a charity to collect it
Lots of Greenpeace members got in touch to say they plan to arrange for a local charity to collect their tree in return for a small donation. There are charity collection schemes operating throughout the UK - visit charityxmastreecollection.com to find one near you. Or you can search on Google for "Charity Christmas tree collection [name of your town]" to see what comes up.
Thanks to Sharon, Sophie and Julian who made this suggestion over on the Greenpeace UK Facebook page.
3. Drop it at your local garden centre
Some garden centres collect old trees, chip them, and then re-use the chippings throughout the rest of the year. So if you know a garden centre near your home, it's worth giving them a call to see if they'll give your old tree a new home.
4. Donate your old tree to a conservation scheme
In some parts of the UK, old Christmas trees are used in important conservation work. In Formby, Merseyside, trees are used to protect sand dunes and sea defences. And in Calderdale, West Yorkshire, they're used to build up hedgerows and safety barriers around Ogden reservoir.
It's best to contact your local council for more info about schemes in your area.
5. Leave it with your garden waste collection
In some parts of the UK, Christmas trees are collected with garden waste - meaning all you have to do is leave the tree outside your front door and the council will pick it up for local composting or chipping. But please note that not all council offer this service, so it's best to check with yours first.
Bonus idea - next Christmas, choose a rented tree
This isn't really a suggestion for what to do with old Christmas trees, more an idea for next year. When we asked how Greenpeace members planned to dispose of their old tree, lots of people got in touch to say they planned to return them and get their deposit back -- as their tree was rented from a local shop.
As The Ecologist explains: Tree hire companies usually grow their spruce in special pots that are sunk into the ground and allow small roots to grow, for eleven months of the year. In December they are lifted and hired out for a month; then in January the pot is sunk back into the ground.
A few schemes that are worth a look include: Forever Green Christmas Trees in South Essex, Gill’s Home & Garden in East Sussex, Trees for Rent in Dorset and RentalClaus.com who deliver throughout Gloucestershire and Bristol.
Is there anything we've missed? Let us know in the comments below.