Plant at leisure, or repent in haste

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(Filed: 30/11/2002)

Trees cause great damage if planted too close to the house, so check the variety you want is right for your garden says Yvonne Thomas

Never buy a tree on impulse. That is one tip I pass on at the start of this tree-planting season, having been seduced by a pretty little sapling which grew surprisingly big and is now, 12 years later, costing £250 to chop down.

Trees can do quite a lot of damage in the wrong place. The annual insurance bill for claims because of them is £300 million in the UK - enough to make anybody paranoid.

Yet the streets are full of big trees that have been planted close to buildings without doing any damage. Large buildings tend to have deep foundations to support them, but if you are planting a tree in the garden, how far should it be from the house for safety? And what sort of tree is suitable?

Oak tree: plant at least 98 feet from your house

Obviously one that's going to grow stout about the waist should not be put too near a wall because it will cause direct damage by pushing it. And surface roots under a thin structure like a path can lift the paving stones.

What is less obvious and more serious is indirect damage. This is caused by a thirsty tree removing so much water from clay soil that it causes shrinkage and, possibly, subsidence.

"The first thing to do," says Bruce Hatton, chairman of the Arboricultural Association, "is to see if the soil is clay, because clay will shrink when water is taken out. Pure sand, or coarse, porous soil doesn't move."

There are grades of clay; some dry out and shrink more than others. Trees can also be divided into heavy, moderate or light drinkers. Heavy drinkers, such as poplars 12,100 gallons (55,000 litres per year) will do most damage in clay soil where a light drinker - birch - may be all right.

Many people think tree roots dig down. They do not. They are shallow, but they spread out. The distance they cover is at least as great as the height of the mature tree. So roots drying out the clay under a house may cause movement and subsidence cracks. Chopping down a big tree can have the opposite effect, known as heave, caused by the clay re-wetting.

It is not all bad news. "Just because you have the roots of a tree under a building does not mean you have a problem," says Harry Pepper at the Tree Advisory Trust. "Roots only go down one to about 5ft (1.5m). And if they come into contact with drains or foundations they go around them not through, unless there are cracks they can get into."

The safest option is still to put an appropriate distance between tree and building, taking soil type into account. There are British standard tables giving recommended planting distances, available from the Tree Advice Trust. But if there is a tall mature tree nearer to the house than recommended, don't worry. It will be comfortably established by now. Trees and buildings can live together.

-- Anonymous, December 02, 2002

Answers

I have an Asian birch that I need to top off. It isn't that old. It is already much taller than it was supposed to grow, and it is threatening the wires to the house with every snowfall. It isn't right under the wires, but it leans in that direction when it snows. Research didn't do me any good on this one.

-- Anonymous, December 02, 2002

We need a fast screen on our north side. I have forsythia out the wazoo and rose of sharon. We're going to plant a great deal of rosa rugosa. We've got tons of free little cedars everywhere. We'd like to plant these things in successive rows near the fence but not in it. We'd like to back up the whole mess with pine, but what kind? We're in severe drought with no relief in sight. White pines we've tried never made it. Any ideas?

-- Anonymous, December 02, 2002

Almost anything you can plant. no matter how drought-resistant, will need water in the early stages. Have you checked with your county extension service for recommendations?

-- Anonymous, December 02, 2002

the extension service is a great suggestion, but I would look at what you have that is starting naturally in your remaining areas.

In other words, use what you have on hand. Unless you are being inundated with imported plants seedlings you should have a good idea of what native flora will handle the drought and existing conditions.

When you do plant, take pictures and maybe even make a drawing of what is where, just in case you have to go back to repair/replace anything.

Forsythia is one of my favorites for up north. also bear claw, which turns red in the winter if I remember correctly.

-- Anonymous, December 02, 2002


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