Mozart, rock and roll and kind words make no difference at all to plants. They certainly won't grow any faster, or produce denser vegetation, simply because they have someone who talks to them regularly or plays them music.
In order to make a plant grow more rapidly, it is necessary to increase its rate of photosynthesis, so that it produces more sugar. It is just a fact of nature that more energy is required to produce more growth. These is almost universal agreement among botanists that the rate at which a plant is able to photosynthesis cannot be affected by sound waves, regardless of whether these are in the form of music or speech. Plants do not have a central nervous system and so far they have not been found to have any sensory cells that are capable of being stimulated by sound waves.