No one has mentioned Rhodohypoxis. Not only are they small, but they are increasingly available (mine came from the local Safeway grocery store). Snobs will probably say they are too common and look too much like Impatiens when in bloom. But their high bloom-to-foliage ratio makes them ideal trough plants in my view (although I'm not growing them that way myself). Several Oxalis come to mind, too, especially little O. depressa (O. inops). Here this is a tidy grower and not invasive (I wish it were more so). The Oxalis is not hardy here, and the Rhodohypoxis is a borderline plant. For something very different, and for a "bog trough", try little Habenaria radiata. (You may see it listed as Platanthera or Pecteilis or Pectelis). This is a very charming little bog orchid which gets to be about eight inches or so high with one or two nickel-sized brilliant white flowers which in silhouette suggest a flying bird. It blooms here in August. This one grows from a fuzzy lemon-seed-sized storage structure and is reputed to prefer dry winter conditions. It has grown outside here for years in my bog trays (where it is wet all year). Years ago I had a group of these in a low broad pot surfaced with moss and bottle gentians: very elegant! I've got some seedlings of Gentiana autumnalis coming along, and hope to combine the two soon. Jim McKenney email@example.com Montgomery County, Maryland zone 7 where the first groups of male robins are passing through and red-bellied woodpeckers and barred owls have joined the chorus: bird song is really picking up now!