Gardens are sculpture in its essence in that they can make you physically aware of the volume of space around every object in the garden.
Your senses become heightened, you become aware that your physical position is a dance, relative to every other being or object in the garden.
Dimensionality, texture, scale, voids and masses are all basic elements of sculpture.
Don't forget duration and TIME.
Gardens make you aware of the elasticity of time. The quickest way to experience Kairos, sacred time is in a garden. Time stops wonderously to allow you to experience a perfect moment: a bird song, a spider web, a flower. Something small that you've slowed down enough to actually experience.
Time also accumulates best in gardens. It does this quietly through the growth of plants to become a patina of years.
Don't just look for flowers in gardens you visit this summer....................
Look for sculpture in how the garden moves you.