I added a small plant to the north-side bed of the Zen garden. It was a Chamaecyparis obtusa 'Just Dandy' that I purchased for a few dollars.
It will grow about 1-3" per year and get to be the size of a beach ball in a couple of years. I like that it maintains its globe shape and it should do well in sun to part shade.
In order to get it into this rock lined bed, I had to remove one large stone to give it more space to grow than was available in the little space that already existed. As it grows, it should fill in the space nicely.