The basic design elements of planting a container are pretty simple: thriller, filler and spiller.
The thriller is the focal point of the pot, usually the tallest plant. Fillers are just that, they fill in gaps and help round out the planting. The spillers are the vines or other plants that trail over the side of the pot.
For decades, the main trailing plant has been variegated vinca vine (V. major). Several years, ago, the chartreuse ‘Margarite’ sweet potato vine (Ipomoea batatas) started earning high marks for its trailing habit.
‘Margarite’ can be a bit of a thug in a pot or hanging basket, frequently over whelming its plant mates. The same with the Wave brand of petunias, which with a spread of 3 feet or more, can completely consume a container. Each of these will work in really large containers, or even better, as a summer groundcover.
For a pot, look for other sweet potato vines, such as Illusion Emerald Lace, which is chartreus, or Midnight Lace, which is purple. Each is a good trailer that reach 2-3 feet, but without the thuggish tendencies of other sweet potato vines.
The natural habit for petunias is to trail, so about any of them will work as a spiller in a pot without consuming it. Among my favorites is Proven Winners’ ‘Royal Velvet’, the country’s best-selling petunia, which has a wonderful fragrance, an attribute frequently bred out of hybrids.
If you are looking for something else trial as a trailer, here are a couple of suggestions:
‘Blue My Mind’, sometimes called a dwarf morning glory (Evolvulus), is a true-blue winner. This sun-loving, heat- and humidity-tolerant annual has silvery-green leaves and blue flowers about the size of a quarter. It gets about 6 inches tall with a 12-15 inch spread.
Creeping wire vine (Muehlenbeckia axillaris) offers a light, delicate foil to larger to containers for sunny to partly sunny locations. It gets about 4 inches tall with a spread of about 18 inches. The dark stems and green leaves provide a nice, contrasting texture to bolder plants, such as petunias and geraniums.
‘Summer Blue Wave’ Torenia is a terrific trailer for shade to part sun, performing much better than any lobelia in a pot or hanging basket. Torenia, sometimes called wishbone flower, comes in other colors, too, including ‘Yellow Moon’, which is yellow with a grape-colored throat.