Ask Mr. Smarty Plants

1. Foreground plants:
Texas Frogfruit ( Phyla nodiflora) is a possibility for one of the foreground plants. It grows only 3-6 inches high and does well in dry or moist soils.

Meadow Violet (Viola sororia) or Missouri Violet (V. missouriensis), considered the same species by some experts, are also possibilities.

If the terrarium is going to be really moist, he could consider one of the Water Clovers, such as Marsilea macropoda or M. vestita, as well as one of the Pennyworts such as Hydrocotyle umbellata or H. verticillata var. verticillata

Sedges might also work for the foreground although they are likely to grow >5 inches tall.

2. Midground plants:
Sedges would be a good choice for the midground plants. Cedar Sedge (Carex planostachys) grows less than a foot tall and is generally happy in dry soils.

Another sedge possibility is Meadow Sedge (C. perdentata) that does well in both dry or moist soils and grows 12-18 inches high.

Maidenhair Fern (Adiantum capillus-veneris) grow 6-12" high and could also be a good plant for the midground area. It will grow in soil-filled depression in rocks.

3. Rear plants:
Ferns such as Southern Shield Fern (Thelypteris kunthii) that can grow as high as 2-3 feet could be a choice for the rear plant, but it does prefer the shade.

A grass such as Little Bluestem ( Schizachyrium scoparium ) is a possibility for the sunny area.

4. Rear glass:
For plants attached to bark hanging against the glass at the back, he might consider one of the epiphytes such as Ballmoss (Tillandsia recurvata) or Spanish moss (Tillandsia usneoides).