I love the Companion Plants that accent Bonsai in our shows.

Right, a tiny Oxalis that blooms all summer, and will bloom all winter too if placed in a sunny window. This one goes into the coldroom each Fall for a long winter's nap, however.
Above left, a 2-inch-tall Erodium with one white flower at the top - at 3 years old it has grown a trunk and can be shown as a mame-size bonsai.  Right, my all-time favorite for companion plants - Japanese Meadow Rue, a tiny dwarf meadow rue originally from the Japan island of Kyushu. The pale pink powderpuffs form in early June and stay on the plant all summer! As if that weren't enough to recommend it, it's completely outdoor-hardy!
EDELWEISS - Recognized the world over as a symbol of Austria and Switzerland. This one survives in a small sunny patch of sand. Yes, just as in the song, the sunny upturned faces greet me every morning when I water. Who can resist returning their smile?
In the shade, another white flower stalk starts to open at the bottom on a very large Hosta - this one is planted behind the garden pond.
IN THE GARDEN
ACCENT PLANTS
Left, Spirea 'Magic Carpet' bloomed in May and is now in its second bloom flush in June.

'Magic Carpet' goes through a number of color changes during the season, and takes readily to pot culture, with the leaves reducing immediately.

I always have a number of babies coming along in tiny pots, to serve as companion plants or small bonsai.  I saw many Spirea accent plantings at the Kokufu annual bonsai show in Tokyo.
On to the Pond Pictures