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City trees and inner-city green spaces are natural air conditioning systems that are essential for the “air conditioning” of cities. A fully grown deciduous tree evaporates up to 400 liters of water on a hot summer day and thus cools its surroundings. They are also effective shade providers, for example a single deciduous tree with a 15m crown diameter can cool an area of 160 m² with its shade. In addition, city trees bind a considerable amount of CO2 and dust.  

Climate change is leading to ever increasing heat loads in city centers. Trees particularly suffer from these extreme weather conditions.


City trees struggle with pollutants from the air, with too small planting areas and too little space for roots, too much light, with the use of salt in winter and with injuries from construction work or accidents. This makes them susceptible to pests such as chestnut leaf miners, Asian longhorn beetles and fungal and bacterial diseases.


Cities such as Frankfurt am Main with its 200,000 city trees already offer tree sponsorships. B.L.U.E. Germany wants to initiate further tree protection campaigns and is looking for supporters for the conservation, new planting and care of urban trees.


But every resident can do something for the trees on their doorstep even without having to spend money. Watering is particularly important for younger trees that have not yet been able to develop a lot of roots. Even before the start of summer, watering should be done in the morning hours or after sunset. Water rather seldom, but in a larger quantity. This increases the chance that the water can sink deeper.

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