No heat is required at all, for such a tiny amount of sugar. I make hummingbird juice all the time and that's 4 to 1, 1/2 cup of sugar dissolves in 2 cups of water with just a bit of stirring or shaking for a couple minutes. Boiling the water is no faster, it just throws off the ratio through...
Uhhh… they don't hear like you, but sound is vibration, plants can detect vibration. vibration physically affects things, wet soil is a great conductor of sound vibrations - the soil is subtly disturbed. Your scope of what it takes to "hear" is too narrow. Deaf people can feel music, why...