Every household has its own Christmas-tree traditions. Some get the Anthea Turner treatment, with only carefully coordinated baubles allowed anywhere near them; in these houses, you suspect that the all-too-perfect presents below are actually empty cardboard boxes. Other trees find themselves, like a benign uncle being dressed up by the children, festooned with every paper Santa ever brought home from school; every novelty decoration sent by an eccentric friend; every beloved glass angel, no matter how chipped. Towering work of art or tinselly mish-mash, it's always the centrepiece.

In most homes, the tradition extends to using either a real tree or an artificial one. Artificial trees have obvious advantages: they cost less because they are reused, and never lose their foliage. But for many people, Christmas is not Christmas without the scent of pine and the ritual of picking needles out of your socks while watching The Great Escape.

The trouble is, of course, that it doesn't seem very 21st-century to be hacking down young trees just to brighten up your hall for a few weeks. Isn't that the sort of behaviour Sting's been warning us about all these years?

Happily, it's not as black-and-white as that. Buying a real tree is not bad for the environment, provided it comes from a sustainably managed plantation where another tree is planted in its place.

If you want to buy a cut tree, at least buy British, ideally from the Forestry Commission or the British Christmas Tree Growers Association (BCTGA).

All Forestry Commission trees are grown sustainably, and almost all of the forests have Forest Stewardship Council (FSC) certification, which demonstrates that the plantation protects biodiversity. Roger Hay, secretary of the BCTGA, explains that they have their own code of practice which advises the minimum use of chemicals of any kind in order to encourage wildlife.

Another good recent option is Caring Christmas Trees, where there is the added benefit of helping vulnerable people at the same time. Caring Christmas Trees operates in six areas of Scotland and assists different charities in different places. Firstly, you decide what size of tree you want, then choose a local centre to collect it from and pick a date for collection. On that date, you go along to your chosen pick-up point and select one from the trees they have in your preferred size.

The prices are similar to what other outlets sell for, the trees are high-quality needle-last firs - but the difference with Caring Christmas Trees is that all profit (roughly 35% per tree) goes to charity. Why must you pre-order instead of just going along on spec? Because that way, the correct number of trees can be cut to order, maximising freshness and minimising waste.

In Glasgow, the charity running the franchise is Impact Arts, a community arts organisation. "If we manage to sell 3000 trees, we can generate £15,000 for working with young people in the city," says director Rachael Arnold. "There are always so many organisations looking for support, but there's never enough money to go round. We wanted to try something different, and reduce our dependence on government grants."

Two of Impact Arts' projects in particular will benefit. The first is Fab Pad, in which young homeless people are helped to paint and decorate their flats to make them more like a home, with the aim that they will be more likely to stay and gain the confidence to take other steps to improve their lives. The other is Creative Pathways, a project to develop enterprise skills with those who are not in education, training or employment.

The Caring Christmas Trees project was the brainchild of a volunteer at another charity, Bethany Christian Trust, which set up the scheme in Edinburgh and Fife in 2005. It was originally designed to raise money for Bethany's winter care shelter, giving homeless people a hot meal and a safe place to sleep, and was an instant success: the charity sold 3000 trees in its first year, instead of the predicted 1000. Running costs for the shelter are around £100,000 a year and the project has been so successful that half of those costs are now covered by its profits. Prime Minister Gordon Brown is a supporter and will be buying his third Caring Christmas Tree this year for his Fife home. As well as Impact Arts in Glasgow, Bethany has sold franchises to Gowrie Care in Dundee and Perth, and Kibble in Paisley.

Around seven million trees are sold in the UK every year, and most are from private plantations, many of which belong to the BCTGA. Broadly speaking, aside from transport emissions, environmentalists have two concerns about plantation-grown trees: the extent of herbicide and pesticide use, and the protection of biodiversity. Caring Christmas Trees come from a plantation where use of herbicides and pesticides is kept to a minimum.

The important thing if buying a cut tree is to ensure that you recycle it when it's time to take down the decorations. The site of tired Christmas trees lying abandoned for the bin men on pavements is not only depressing but bad for the environment. You can check with your local council to see if they recycle trees.

One way to avoid that scenario altogether is to buy a potted Christmas tree that can be brought in temporarily and then put back outside again once the festive season is over.

And what about plastic trees? You might still think they're the best option, but scientific evidence suggests that, unless you reuse the same one for a decade or more, substantially more carbon dioxide is used in the manufacturing and life cycle of your plastic tree than is used in the production of a single-use natural Christmas tree. Besides, PVC takes centuries to decay and produces toxins.

So go on, treat yourself to a real tree this year - and help spread the Christmas cheer.

Getting the best from your tree