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Noise Pollution
Keeping out unwanted sound
There are two things to keep in mind about noise: it travels in a straight line and it bounces off of hard surfaces. Different sound waves have different shapes, therefore different plants will have a different effect on them.
So, if you try to block out noise with hard surfaces such as wooden boards or walls, you risk simply redirecting it. A muffling effect can be created with a wall of foliage -- leaves and stems will absorb noise. A well-placed leafy plant between you and that pesky air-conditioner across the street can work wonders.
How do you choose the right plants? Match leaf size to sound frequency: High frequency noises need a lot of small dense leaves packed close together. Lower tones are best muted by bigger leaved plants. But keep in mind, if you jam-pack your balcony with plants to deaden all noise your home will be claustrophobic and depressing.
As the urban Buddah says: "You live in a city - get over it."