Thirsty Towers

TREES are great travellers! They move effortlessly through time and around the world. Many have survived since before the ice age without any change in their habit or appearance.

Trees, like us, are survivors but we are inclined to abuse them by felling too many broadleaved varieties (for building purposes and road projects), through vandalism, and poor replanting rates.

For all that, we “feel” for trees. Over two hundred years ago the German naturalist, Alexander von Humbolt, said “we feel for trees because we identify with them. Like us, they are small and helpless when they are young. Like us, they take pride in their power when they come to maturity. And like us, they come to a tottering old age when they are once again dependent on others for survival”.

Visiting trees from every continent can take root in your garden, the only restrictions being extremes of climate and available space. But did you know that trees have a drink problem, and that their quest for water may lead to property damage in their vicinity? Some varieties are bigger drinkers than others. For instance, a fully grown apple tree can drink 4,400 gallons of water per year whilst a mature poplar will draw up 12,000 gallons. When trees are vigorous and growing strongly they will drink even more and this can affect the ground beneath their spread. Clay soil shrinks alarmingly when it is desiccated by a heavy drinker and the higher the plasticity (the smaller the particles in the clay) the more it shrinks.

As seen, the biggest drinkers are the poplars followed in turn by willow, oak, eucalyptus and the dreaded leylandii. Those with a moderate thirst include ash, alder, blackthorn, cherry, hawthorn, horse chestnut, laburnum, lime, plane, pine, yew, apple, pear, and plum. Low consumers of water include beech, birch, holly, magnolia mulberry and rowan. Lucky for me, the giant silver birch growing within 15 feet of where I write is a low consumer of moisture and quite unlikely to ever cause damage to the garden studio.

And yet all trees, no matter how tall, have shallow roots. They go out not down. Even a big tree’s roots rarely go further down than 6 feet and most are in the first two feet. They rarely find their way down to the water table preferring to rely on rain at all times. Roots anchor the tree and draw in moisture but all the heavy supporting roots are in the surface soil.

That root spread is at least equal to the height of the tree and could be more if the soil is infertile, so always check from the nurseryman what the final height of your purchase will be when mature.

Points to consider include;

* How much of a drinker is your choice based on the information above?

* What kind of soil do you have, clay, chalk, sand, coarse? Light porous soils do not move.

* How deep are the nearest foundations? Those over six feet deep won’t be interfered with by roots

* Will your choice ultimately affect the light, dry out the lawn, or stress nearby trees?

* Will the tree trunk push at a structure when it has grown to full girth?

* Buying a new tree can be a difficult and exasperating experience, so choose carefully and seek advice from the experts if you are unsure.