If choosing a cut real Christmas tree, remember that more than half its weight will be water, so keeping it in water indoors is the most effective way of maintaining its freshness and minimizing needle loss. Apparently most Christmas trees went up last weekend, so five weeks in a hot house is a long time to expect a tree to hang onto its needles without a drink!
When you buy your real tree, acclimatising it to the indoors gradually will also help prevent it just shedding its needles in the unfamiliar heat. If you know what a hot flush is like, you will sympathise!
Remove about a 1/2-inch from the base of the trunk and put it into water as soon as you get it home and then put in the porch or garage for a day or two before taking it indoors.
Once the tree is indoors and dressed it will need topping up with water regularly – a large tree could drink as much as a gallon of water a day in its first week indoors.