I think these notes comes from "Magic of Trees and Stones" by Katsuo Saito.
...a means of self-expression using a variety of images drawn from nature. Rather than recreating nature as found in the real world, were distilled images and arranging these poetic fragments into an amalgam in the garden.
Heian Gardens: not perceived as total compositions but rather as a collection of poetic images. But images were not always first-hand, but images from poetry.
The use of existing, commonly understood poetic images as a basis for garden design.
Much of Japanese poetry was given over to nature description.
"Pine Tree" and "Wait" both equals "Matsu". So the pine tree becomes a suggestion of waiting, in particular - yearning for a lover or the resolution of an impossible situation.