Plant of the Month for September, 2016

ruellia humilis header
Ruellia humilis

 (roo-EL-ee-uh  HEW-mil-is)

General Information:

Petunias are very popular in the garden but in colder climates they are annuals. The wild petunia, Ruellia humilis, is a hardy perennial that can take the place of other petunias.

Ruellia humilis:photo by Robert Pavlis

Ruellia humilis, by Robert Pavlis

Ruellia humilis has a number of common names including prairie petunia, fringe-leaf wild petunia, hairy ruellia, hairy wild petunia and the fringe-leaf ruellia. With so many names you would expect this to be a popular garden plant but it's not. It is quite rare in cultivation. That’s hard to believe since it is easy to grow and flowers for a long time – late spring to fall.

Ruellia humilis looks like a petunia, is called a petunia, but it is not a petunia. It is a member of the acanthaceae family. The common garden petunia is in the genus Petunia and the family Solanaceae, which also includes potatoes and tomatoes.

Ruellia humilis:photo by Robert Pavlis

Ruellia humilis, by Robert Pavlis

Ruellia humilis:photo by Robert Pavlis

Ruellia humilis, by Robert Pavlis

The wild petunia grows to about 30 cm (1 ft) in height and spreads 2 or 3 times that size. Flowering occurs along the tip of the stem with one or two flowers open at a time. Each flower lasts one day and after they drop off, new flowers open above the old ones. The display is subdued since the number of flowers open at any one time is low but it more than makes up for this by flowering  for many weeks.  

It is easy to grow from seed and may seed around a bit more than one likes in zone 5, but it’s not weedy. The seedlings are a bit difficult to pull out without the use of a trowel or similar device. It is reported to be invasive in Florida where it spreads by long-running stolons.

 In North America it is an uncommon native plant that is host to the Buckeye and several other butterfly species.

Note: Sept 2017: After growing this plant for a while I find that it seeds easily and the seedlings are not easy to pull out.

Life Cycle: perennial

Height: 45cm (1.5 ft)

Bloom Time: late spring until fall

Natural Range: Central and Eastern North America, including Texas

Habitat: woodland edges, open thickets

Synonyms:  Ruellia ciliosa, Ruellia humilis var. longiflora


Light: full sun to part shade

Soil: humusy to sandy, not fussy

Water: drought tolerant once established

USDA Hardiness:  Zone: 3 - 9

Propagation: seed, division, cuttings

Seedex availability (ORG&HPS annual Seed Exchange): occasionally


Sow @ 4°C for 3 months, then place @ 20°C for 3 months.
4°C x 14 weeks (very important for best germination), then 20°C
Robert Pavlis