Finer Balances for the Best UK Gardening

Finer Balances for the Best UK Gardening

To be less hot in summer, especially in cities, you have to plant! Trees in the streets, green spaces, plant walls: plants refresh the air. But why, how?

With vegetation, the temperature drops by several degrees

We have all seen it: it is cooler where there are plants (trees, lawns, plant walls). This is especially evident in the city : in the height of summer, in sunny weather, it is less hot under trees or in a park. In green areas (a street planted with trees for example), it is actually several degrees lower than where the plant cover is absent and the concrete ubiquitous (street not planted).

In the shade of the trees

This is called the ICU, for Urban Heat Islands: in fact, in the city, buildings, tarmac, roofs store solar energy during the day in the form of heat, to restore it at night (after a hot day and sunny, the walls of the facades, the shutters of the windows, the asphalt of the sidewalks, etc. remain hot long after dark. This is the reason why, in the city, the temperatures struggle to drop at night during heat wave).

The temperature in large cities in summer is thus several degrees higher than that observed in the surrounding countryside: in Paris for example, in good weather, this temperature difference can reach 7 to 8 ° C. For the uk gardening 24  this is important.

How to explain this cooling of the air by plants?

Shade and no heat storage

First, by creating shade , a plant screen prevents solar radiation from reaching the surface likely to store heat , whether it is a floor or a facade (concrete, metal, bitumen).

It is therefore not only less hot thanks to the shade, but moreover, solar energy being absorbed largely by the plant cover (plants also consume a part of this solar energy for photosynthesis ), it n is not stored or released overnight: temperatures climb less during the day and drop more at night.

Less reverberation

Another effect of plants: the plant cover prevents the reverberation of the sun’s rays from one facade to another, or from the ground to the facades. Plants “break” the sun’s rays and therefore hinder this phenomenon of “heat boxes” that can be observed in a street framed by two rows of facades, or in a clear area surrounded by buildings (forecourt, courtyards, squares).

Leaf perspiration to refresh Plants sweat to cool: the water drawn from the roots is rejected by the leaves in the form of water vapor, which allows the leaves to maintain an acceptable temperature. This leaf transpiration refreshes the ambient air, provided that the roots of the plants have water at their disposal (they must therefore be watered, or they must go to draw water in depth … something that the trees do very well).