SELECTING a Christmas tree is not the simple matter it once was. Until recently there was only a choice between a straightforward Norway spruce and an artificial tinsel tree. Nowadays there are a number of different conifers which masquerade as Christmas trees.

Some allegedly hold on to their needles for longer than others, but it is difficult to understand why, for in most cases there is no scientific reason for this. The aftercare a Christmas tree receives, irrespective of species, is the main factor in determining whether it will survive until Twelfth Night.

The choice of a Christmas tree with or without roots is of little consequence unless the tree has been grown in a pot and has a good potball. Such trees, if handled with care can be kept from year to year.

Any tree over 3ft high which has been dug out of a field with its roots intact has less than a 50 per cent chance of lasting long enough to become re-established in the garden after Christmas, although there are gardeners who regularly and successfully lift and bring a tree into the home year after year.

Whether you choose a cut or bare-rooted tree, the most important factor in ensuring its survival for the Christmas period is to have it in the house for as short a time as possible. Ideally not moving it inside until Christmas Eve.

Warm temperatures and a dry atmosphere cause Christmas trees to desiccate quickly, leading to the browning of branch tips and needle drop. The cool damp conditions of December weather outdoors are much more congenial to their well being.

Once indoors the provision of water is vital. Even trees with cut stems will take up a considerable amount of water. Recognising this, manufacturers have now designed containers with clamps which hold the trunk of the tree and a reservoir for water. Of course the tree can still be planted in damp soil in a pot with reasonable success.

Trees which are fixed to blocks of wood or logs have a much reduced chance of surviving without needle drop. The only way to assist them is to spray the leaves with a Christmas tree spray, the same produce that is used by landscapers for spraying the foliage of evergreen shrubs before they are transplanted. It prevents excessive moisture loss and, in the case of cut Christmas trees, prolongs their life by two or more weeks.

If you consider a tree other than the traditional Norway spruce, you could not do better than look to the Noble fir. This is a lovely dark green conifer of symmetrical habit which, unlike the Norway spruce, is not prickly to the touch.

The Concolor fir is also very acceptable in shape, size and habit, but it has a bluish green foliage which some find unacceptable at Christmas. This can happen with the pines as well, although it is their shape rather than any colouration which makes them less desirable.

WHAT'S NEW

l Spring Falls is a brightly coloured mixture of aubretia.

l Sunshine Carpet is a mixed coloured strain of fibrous rooted begonias with both bronze and green foliage.

GARDENERS' QUESTIONS

Q I have an overgrown wisteria. When and how should I prune it?

A Now that your wisteria is dormant it is a good time for removing really bulky material. Cut it back hard to the main stems. Summer pruning of soft growth will also help to reduce bulk in the future. Reduce all lateral shoots to three pairs of leaves.

Q I have just bought some shallot bulbs and I have been told to plant them on the shortest day. Is this correct?

A Traditionally shallots have been planted on the shortest day of the year and harvested on the longest day. In practice it is preferable to plant when the ground is fit, usually around mid-February. In the meantime keep the sets cool and dry.

Q I have a lovely indoor Christmas azalea in full flower. Is it possible to propagate it and if so how do I do it?

A When it has finished flowering choose short non-flowered shoots about 2in long with a heel of old wood attached. Root in a mixture of equal parts of peat and sharp sand on the window ledge.