The Tree Root Myth

The Tree Root Myth Has Been Around For Years, But Science Disproves It Root & Branch. Learn More About Tree Root Spread, Depth And Reach Below.

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When I went to school I was taught that trees were shaped a bit like a dumb bell. We were told that the root end sat in the ground and was roughly the same size, spread and density as the bit on top of the trunk. It never made sense to me as when I saw trees blow over in storms I could see the roots were much smaller. When I questioned it I was told these were abnormal trees and had blown over because of inadequate roots. Teacher was meant to know best and most kids believed them. I was a rebel and didn’t believe a word of it. Today science is able to tell us much more.

Common Sense Tree Root Size Signs

If the size of upturned roots weren’t enough maybe we should look for other clues. For example, when digging in the garden why did I frequently find tree roots a good distance beyond the spread of the tree canopy? And why did we often find suckers of elm, sumac and other trees coming up long distances from the nearest trees?

The Truth About Tree Roots

When a tree starts to grow it sends down a tap root which grows straight downwards. Then it sends out lateral roots. these are often close to horizontal and not only help it anchor in the ground but produce fine roots through which the tree gets its water and nutrients.

So in the early stages the tree is quite close to the dumbbell type growth I was told about. But it’s a small tree, maybe a foot high and with roots going down around 10-12 inches.

But very soon the tree gets limited by a range of potential problems. For example, sometimes the topsoil is shallow and sits on top of rock, shale to compacted subsoil. In this cases it cannot keep going down. On other occasions the top soil is quite compressed and this limit both the taproot and the laterals. And where these “pans” exist there are drainage problems. not only are the tree roots restricted, the water cant get away. And wet soil is airless. And without oxygen at its roots the tree suffers. It literally “drowns”. In winter it can tolerate wet soil for longer, because it is dormant. But during the growing season most trees cant tolerate a really wet soil. The exceptions are the alders, willows and similar tha throw alongside streams, rivers and wet places. But even they have their limits.

What happens in the typical tree, whether it hits consolidated ground or not, is that the tap roots soon splits into several smaller roots and don’t go too deep. Three meters deep is exceptional. And the laterals spread out beyond the canopy and “drip line”, often many metres beyond the tree canopy. And as it does it tends to keep in the top metre of soil. Very few roots go down below this level. Most actually stay in the top foot of soil, many in the top foot.

Should the soil be very shallow due to bedrock or compaction the tree’s roots will hug the surface levels. But should it find a fissure in which it can burrow it will seek to do so. Any roots managing this will then develop as normal in that location.

Naturally Shallow Rooted Trees Defy The Tree Root Myth

Though all trees are shallow rooted some are naturally more shallow rooted than others. Hilltops are often devoid of deep soils and yet some trees prosper on hill tops. Beech is a typical example of a shallow rooted tree that thrives on hill tops.

If you’ve a garden with very shallow soils consider any of the following as potential species to grow.

Beech, Fagus spp.
Birch, Betula spp.
Norway maple, Acer platanoides.
Sugar maple, Acer saccharum.
Cottonwood, Populus deltoides.
Hackberry, Celtis occidentalis.
Silver maple, Acer saccharinum.
Spruce, Picea spp.

The Effect of Soil Density, Aeration and Fertility

People and cattle both love sheltering from the rain and sun under trees. that’s good for them, but not always good for the tree.

Why?

Because the soil gets compacted over the top of the shallow roots. This means water has problems penetrating and so does air. without air and moisture trees die.

The 1987 Storm Taught Us So Much

The night of October 15th and early morning of October 16th 1987 saw a huge storm hit the UK. Worst hit were Sussex, Suffolk and Kent. I remember driving from Bedfordshire To Hants the next morning to discover power lines were down across range country and petrol stations unable to pump fuel. But worse still were the hundreds of thousands of trees that were uprooted. It was the worse storm in 200 years.

But every cloud and storm has a silver lining. At Kew the teams spent years sorting out the trees. Cutting up ancient trees with unrivalled histories. But as the years rolled by a marvellous thing happened. trees that had for years struggled due to soil compaction started to grow better than ever before. It took a while to realise why, but the answer is simple.

The survivors that hadn’t blown right over had blown so hard that they had literally made rather ground shake. Their roots had strained and lifted the soil. Some trees had blown partially over in the wind only to fall back into place when the storm abated.

It was like they had been plucked from the soil by a giant hand and then dropped back into place. And once back they rooted back in and grew away really well.

Since learning this arborists have developed a new technique. They can’t manually lift a full grown tree from the soil and replant it. But they can drive steel tubes in to the soil under trees and pump compressed air into the soil. This breaks up the compacted soils and breathes life back into old trees.

For more in depth research and tree information read the following

https://www.trees.org.uk/Trees.org.uk/files/61/6181f2b7-e35d-4075-832f-5e230d16aa9e.pdf