The festive season for Christmas trees seems to have jumped a month, as retailers have now been selling real trees for several weeks to the public, despite advice from the British Christmas Tree Growers Association not to buy your tree earlier than December 1.

Homebase, B&Q and Asda have had trees in some of their stores for several weeks, while even John Lewis has started selling real trees online for the first time.

I personally remain unconvinced about buying a Christmas tree online as shapes do vary and there is limited scope for returning it if it's too wide, dense or simply doesn't fit the shape of your space.

But if you've already decked the halls with boughs of holly and put the baubles and tinsel on your Christmas tree, how are you going to stop it from looking like a dried-up old offering by December 25, with more needles on the floor than on the branches?

Well, if you are still looking for a cut real tree, make sure you saw around an inch off the base before you buy, which will open the pores of the tree, albeit temporarily. You need to plunge the tree butt in a bucket of water immediately after cutting it, so the tree can absorb moisture and the pores don't have a chance to close up again.

When the tree is brought indoors, mount it in a water-holding stand and place it away from direct heat, such as a radiator. Keep the container topped up with water every day; you will be surprised how much the tree drinks.

When buying your tree, Harry Brightwell, secretary of the British Christmas Tree Growers Association, advises: "A fresh tree will have a healthy green appearance with few browning needles.

"Needles should be flexible and not fall off if you run a branch through your hand. Raise the tree a few inches off the ground and drop it on the butt end. Very few green needles should drop off the tree but it is normal for a few inner brown needles to drop off."

Prices are likely to be much the same as last year. B&Q is charging £35 for a medium Nordmann fir (4ft 11in-6ft 6in) and £20 for a similar sized Norway spruce, while from Homebase a 5ft-6ft cut Nordmann fir is £35 and a similar sized Fraser fir is £30.

About 80% of the trees sold are Nordmann fir, about 10-15 per cent Norway spruce, and the remainder are lesser known varieties including the Fraser fir.

Gardeners may opt for container-grown trees, grown in pots from seedling stage, which are able to develop a good root system and can be planted in the garden afterwards. However, beware of similar-sounding 'containerised' trees, warns Which? Gardening, the Consumers' Association magazine. These trees are grown in a field then dug up and put into a pot just before sale. They often lose a lot of roots in the process and looked dull and lifeless at the end of a trial carried out by Which?

Anyone keeping a container-grown tree should:

Keep it in the house for no more than two weeks. If necessary, you can keep your tree in a sheltered spot outside until you're ready to bring it in;

Put a saucer under the pot to protect your furniture/floor,or place the pot inside another one without drainage holes.

Choose a cool spot, away from radiators and fires, to prevent the tree from overheating. It should have some natural daylight.

Water regularly and don't let it dry out - but don't leave it sitting in water. Try using ice cubes, which also help to keep the roots cool.

To keep the tree growing after the festive season, put it outside initially in a sheltered spot, next to a house wall for a few weeks, covering it with horticultural fleece if hard frost is forecast.

Repot the tree every few years when its roots outgrow the container, replanting it in ericaceous compost mixed with grit for extra drainage, feeding it with a low dose of liquid feed from spring to autumn. Most importantly, don't let it dry out.

  • The full report on potted Christmas trees can be found in the December issue of Which? Gardening. For more information, visit which.co.uk/signup

BEST OF THE BUNCH - Winter-flowering heather (Erica carnea)

Whether you're using it to brighten up winter pots or in beds and borders for a splash of colour, winter-flowering heather generally won't let you down. Available in shades ranging from white to purple, this low-growing evergreen prefers well-drained, acid soil with plenty of added organic matter, preferably ericaceous compost, in full sun. They make a good ground-covering carpet when planted closely in numbers as well as a lovely temporary addition to winter pots and hanging baskets. Good varieties include 'Springwood White' and 'King George', a mauve-pink type with a long flowering season. Give them a trim with shears after flowering but don't cut back into old wood or they won't recover.

GOOD ENOUGH TO EAT - Harvesting parsnips

You can't beat parsnips as a winter veg, their sweet flavour making a perfect addition to soups and stews, or roasted with a Parmesan coating, or even with maple syrup, to make the perfect accompaniment with a Sunday joint. You can start lifting them as baby vegetables in early summer, digging them up carefully with a fork, but most gardeners leave it till winter, when the foliage has died back and the first frosts arrive, turning the starch content into sugars. If you harvest them now before the ground becomes too hard to dig them out, arrange the roots in boxes so they are not touching, in layers of sand, and put them in a dry shed. Good varieties include Countess, a canker-resistant type, and Gladiator, which has large, smooth white roots and will grow in most soils.

WHAT TO DO THIS WEEK

  • Continue to scoop leaves and dead plant debris out of ponds;
  • Firm around newly planted stock as frosts can lift the soil;
  • Make sure bird feeders and baths are kept topped up and put out fresh water each day;
  • Prune greenhouse vines when all leaves have fallen and the vine is dormant;
  • If holly branches carrying berries are to be used as festive decorations, cover them with nets to keep hungry birds away;
  • Draw soil up round the stems of Brussels sprouts and other brassicas for support;
  • Lift and store swede and turnip for winter use;
  • Watch out for mice in sheds and greenhouses, especially where you are storing fruit and vegetables;
  • Continue to dig over the vegetable patch while the ground is still workable;
  • Prepare large deciduous shrubs for moving, if they have outgrown their space or you need to reorganise the garden;
  • Dig up roots of chive and mint to force on a warm windowsill