Size matters: Be careful when choosing a new tree or you might have a monster on your hands

Now is the perfect time to plant a new tree but you need to choose well – and put in the after-care, says Anna Pavord

The Great Storm of autumn 1987 was a wake-up call for Britain. Initial estimates put the number of trees lost at two million. In the end, the sum came to seven times that, and, disorientated by the shock of it all, it took a while to see that any good could come out of that savage night. But it did. We'd got lazy about our trees. We took them for granted. We somehow thought they'd always be there.

And then they weren't. The net result has been that in the 25 years since that cataclysmic storm, at least five hundred million saplings have been planted in Britain. We've never scored high in European 'tree cover' league tables but now, at least, we've got more of the leafy stuff than we've had for 150 years or more.

But there is always room for another tree, particularly in built-up areas. Sharon Johnson, chief executive of Trees for Cities, points out the practical, as well as the aesthetic advantages they can provide. They clean the air. They provide shade (though we rarely needed that this summer). Perhaps most important of all, given the staggering amount of rain that has fallen this year, their roots absorb a great deal of water.

Now, it is easy enough to plant a tree. Ensuring a future for it is a different matter. As babies in prams are irresistible, so winsome little larches, oaks and monkey puzzles look enticing in pots at the garden centre. But (though tempted) you don't chuck out your baby when it has grown into an unmanageable teenager. So it's unfair to chop down a tree when it has grown too big for the space that you should never have put it in anyway.

If you are thinking of planting between now and Christmas (and you should be – it's the best of all seasons to plant), have very f clearly in your head the eventual size of the tree you want. Pace out 10m (30ft) on the ground and imagine that space filled with branches. Think too, what the tree is likely to do for your neighbours. Will it block out their sun for most of the day? Think about the habit of the tree. In small spaces, trees that go up rather than out are generally easier to manage.

Weeping willows are disastrous choices for small gardens, as are blue cedars. Both, unfortunately for them, look wonderful as babies, but the willow makes a tree 13m (40ft) high and wide, underneath which nothing will grow and the cedar, if allowed to express its soul in its own way, will soar to 43m (130ft). That's big.

Then there's the aftercare. Easy enough to plant, as the tree-planting schemes of recent years have shown: trees in new housing estates, trees along suburban roads… But who waters them in their first summer? Nobody, to judge from the death rate. The summer following planting is the most testing time for a newly-planted tree, and without TLC, planting is pointless.

We get an easy fix of concern for the environment when we trundle bottles to the bottle bank, recycle newspapers, use bio-friendly washing powder, sprout conkers in yogurt pots. But the long-term commitment to bring the resulting seedling horse chestnut within sight of maturity, has to go hand-in-hand with the God-like buzz of creating it.

So: you have done your homework and selected the right tree for the right place. You have resisted the temptation to scoop up some container-grown bargain at the garden centre. You have either grown native trees from local beech mast, hazelnuts, holly berries, conkers and acorns. Or you have sorted out a nursery where you can buy a 'bare-root' tree; that is, one that has been grown in the open ground. These are lifted anytime after leaf fall, traditionally on 5 November.

The advantage of a bare-root tree is its superior root system, which cannot develop in a pot. The roots, with nowhere to go, spiral like demented snakes. The trees never produce big, strong, anchor roots. The exceptions are conifers, which have compact rootballs, and eucalyptus, liriodendron, nothofagus (Southern beech) and davidia, which all resent having their roots disturbed.

There's another reason why bare-root trees establish better than container-grown ones. Growing in open ground, the same as, or even worse than the ground in which you are going to replant them, the roots have been used to pitting their wits against stones and impenetrable clay. They have developed muscle. Container-grown trees, usually raised in soft, emollient, loam-free compost, won't have had to work very hard for a living.

If you plant a tree this side of Christmas, then its roots will go on growing until the turn of the year. It is a great advantage to a tree to be able to settle into its new surroundings, and get its roots comfortably within reach of food and drink, before the branches on top start calling for supplies.

The actual planting is simple. Start by digging a hole at least twice as big as the one you first thought of. Current thinking is that a square hole is better than a round one, because it encourages roots to explore. Settle the tree in the hole, checking that you have dug deep enough. A tide mark on the trunk usually gives a clue to the correct depth. Too deep is as bad, if not worse than not deep enough. Spread out the tree's roots so that they do not cross over each other. Gradually fill in the hole, using the soil you dug out, mixed with a few handfuls of bonemeal. Jiggle the tree up and down so that the compost works its way between the roots.

Firm this first layer of compost with your fists. Continue to backfill with earth, firming as you go. Water the tree and, to conserve moisture, spread a thick layer of mulch (rotted leaves, farmyard manure, mushroom compost) in a circle round the trunk. Young trees (called whips, or feathers) settle more easily than bigger ones. They don't need staking. And most important of all, they are cheaper.