The smallest vascular plant in the world is named Wolffia arrhiza. This miniature plant is a millimeter in length and weighs only 150 micrograms! It grows in ponds and swamps of Africa, Asia and Europe. Bearing no root, wolffia is composed of a single spherical leave that floats on the water surface and produces a tiny flower comprising only one pistil and one stamen.
Failing to cultivate wolffia in your garden, you can still create a nice arrangement made of miniature plants. Some bromeliads, cacti and succulents sold in garden centers are so small they can certainly satisfy your desire for miniaturization. Let your imagination go and grow them in small containers made with wine corks, thimbles, test tubes or kids dinnerware (bowls, cups, teapots, etc.). Very creative gardeners will even make necklaces or earrings with these miniature plants!
Outside, your thumbnail arrangement can be made up of dwarf perennial plants such as sweet flag ‘Minimus Aureus’ (Acorus gramineus ‘Minimus Aureus’), a cute grass whose golden foliage reaches 7 cm in height, false cypress ‘Tsukumo’ (Chamaecyparis pisifera ‘Tsukumo’), a small conifer with a rounded habit that grows 4 to 6 mm per year, and Corsican mint (Mentha requienii), a nice perennial ground cover with fragrant leaves that are 3 mm in diameter.