All professionals have myths that they have to regularly counter and in my work as a landscape architect I regularly come across a number that persist.   I’ve drawn up my top three but there are many more!

Myth #1 – All Trees Have Tap Roots

Truth – Very few trees have any type of tap root.   They are not dandelions!   Of the 4511 trees surveyed after the October 1987 storm by the Royal Botanical Gardens at Kew only 2.4 % had taproots.   Most people don’t realise that between 90 and 99% of a tree’s roots are in the top 1m of soil.

With their roots so close to the surface they are very susceptible to damage so that large truck trundling close to a tree won’t just break overhanging branches but could also be causing severe damage to the roots.   As mature trees can take many years to die the damage may take a long time to come to light.

To ensure that you protect the full root protection zone (RPA) for each tree that you want to retain you need to commission a report by a qualified arboriculturist early in your project.   They will also help you assess the health of each tree as well as the amenity value.

Once you have the RPA for each tree your landscape architect can work out the line of the tree protection fencing which should be done to British Standard Trees in relation to Construction – Recommendation (B.S. 5837 2005)   And no, the area inside the tree protection fencing is not somewhere to store that pallet of slabs.

You can find out more in this useful Forestry Commission document (PDF download)

Myth #2 – Soil Is Just Soil

Truth – soil is full of micro-organisms that need air and water to survive.   There can be up to 5 billion bacteria in just a teaspoon of soil and most of these need light and air to function.   The numerous micro-organisms in soil are vital to soil health, and healthy soil means healthy plants.

It can take up to 500 years to produce just 2cm of topsoil so it is essentially a non-renewable resource.   It is quite easy to degrade or even kill soil by mistreatment.   I’m always amazed how few contractors know that that when they store their topsoil in a 5 metre high mound in just a few weeks much of that soil will be too degraded to use. The soil in the centre of the mound becomes anaerobic, or free of oxygen.   Soil weighs about 2 tonnes per cubic metres so at the base of a large soil mound the pressure will be substantial and the loose, crumbly rich fruit cake texture that is typical of healthy topsoil will be lost .   Part of the myth is that adding some compost to the soil will improve it enough to be used for landscape works .   The soil might hold up the plants long enough to sell the house but long term the chances of plant survival are slim.

For more information see the Construction Code of Practice for the Sustainable Use of Soils on Construction Sites produced by Defra (PDF download)

Myth #3 – A Few Weeds Won’t Do Any Harm

Truth – in private gardens I’m a fan of letting some weeds grow as they are a wonderful resource for wildlife.   However on large scale planting schemes where establishing the planting can be part of the planning conditions control of weed growth between plants is vital.   The facts are staggering – effective weed control can increase survival rates by 50% and growth rates by 80%.   Weeds compete for water, nutrients and light and can choke out your planting scheme. How weeds are be controlled should be detailed in your landscape specification and a maintenance schedule agreed with your landscape contractor.

What are the myths in your profession?   I’d love to know!