Why these plants might be robust possibilities for a shade garden

Joshua Siskin writes about gardening in Southern California each week.

Each member of the Acanthus family of plants (Acanthaceaae) has a unique style that makes it hard to forget. 

Acanthus comes from the Greek word for thorn but most of the plants in question are hardly thorny. The family name is taken from Acanthus (one of its genera), some of whose species have spiny leaves. 

Yet the most commonly encountered Acanthus ornamental is bear’s breech, whose Latin name of Acanthus mollis literally means “soft thorns,” in reference to the fact that its deeply lobed leaves — while technically prickly — have the softest prickles imaginable. The ancient Greeks considered Acanthus leaves, reaching two feet in length while deeply lobed and crisply cut, to be the most ornamental in the plant kingdom and carved them into the tops of Corinthian columns. 

If you are looking for a background plant for a shade garden, Acanthus mollie is the one to choose since it reaches a height of five feet. Leaves are the lushest emerald green and the plant spreads thanks to its tuberous roots. These roots allow it to withstand long periods of drought where all the leaves may die back but the moment it is given water, it speedily returns to its former leafy beauty. It also sends up spikes up to four feet tall featuring white flowers hooded by protective bracts that have hints of purple, pink, green, and gray. 

Bush violet (Barleria obtusa) is a robust shrub in the Acanthus family that grows three feet tall by five feet wide. It may expand its reach considerably due to the fact that wherever its stems touch the ground, they take root. Masses of violet blooms that attract birds, bees, and butterflies appear on stem ends in fall and winter. Firecracker plant (Dicliptera squarrosa/suberecta) has fiery orange-red blooms and fuzzy gray foliage, growing two feet tall by three feet wide. This plant is extremely drought-tolerant and is at the very top of the list of plants that attract hummingbirds. Ribbon bush (Hypoestes aristata) flowers magnificently and abundantly in fall and winter, showing off lavender-pink blooms so numerous that its foliage is virtually hidden. All of the above can be found at nurseries supplied by San Marcos Growers (smgrowers.com).

There are several distinctive indoor plants in the Acanthus family. Aphelandra squarrosa has large yellow flowers and leaves with fluorescent white veins. Fittonia, known as the nerve plant, has smaller leaves with finer white veins. Both Pseuderanthemum atropurpureum var.Tricolor and Hemigraphis alternata sport foliage that is displayed in various combinations of pink, cream and purple. Finally, the polka dot plant (Hypoestes phyllostachya) has green leaves with white, pink, or red dots and splotches.

Here, I must confess my inspiration for writing about the Acanthus family of plants came from an email I received from Matthew Hunt, who gardens in San Clemente, and regaled his Mexican petunia (Ruellia brittoniana) experience. Mexican petunia is a distinguished member of the Acanthus family. The scientific name of Ruellia honors a 16th-century French physician-horticulturist named Jean Ruelle. 

Mexican petunia grows in sunny to partial shade exposures — flowering more in the sun — and is tolerant of a wide range of soil conditions, from dry to boggy. So if you have a pond and want something to plant on the wet ground around it, choose Mexican petunia. Yet if you have a garden that you never water more than twice a week – even in the hottest weather – you can plant it there too, as well as in containers.

Unrelated to the true petunia, Mexican petunia’s gramophone-shaped lavender-blue flowers suggest affinity with the petunia species. This is truly a delightful plant owing to its carefree growth habit and prolific flowering throughout the summer and fall. It grows in clumps that are three feet tall and half as wide but will increase its girth vegetatively, especially when soil is kept moist, through underground root-thickenings known as rhizomes. It will also expand its garden presence through self-sowing. Finally, its semi-succulent stems are an invitation to propagate it in the simplest possible way. Take six to eight-inch cuttings, remove the bottom leaves, and place in a vase holding a few inches of water. Soon you will see roots emerge from the cuttings and, after two to three weeks, you can plant them. There is some complaint that Mexican petunia seeds too freely and may become weedy. I have never found this to be the case but if you are concerned about this possibility, plant Purple Showers, a sterile variety.

Hunt is growing Southern Star Pink, a dwarf Ruellia variety that reaches one foot in height. Blue and white flowered dwarfs are also available. “The stuff breaks really easily,” he writes. “When someone brings a dog over to visit mine, you can see the trails they’ve run through since it snaps off so easily. But it grows back with a vengeance.  Even snapped-off pieces will start to root. In our yard, my wife usually snaps it all off to the ground in March, and in a few months it looks great. But out in the yard, it’s two to three feet tall because she didn’t prune it back this year.” Although promoted as staying one foot tall, the dwarf types may grow taller, especially when the plants in question sprout on site from seeds dropped by mother plants. What grows from a seed is never entirely predictable and often a surprise.

California native of the week: Matthew Hunt also grows and extols Ruellia californica. It’s a shrub with a height and girth, at maturity, of four feet. It is more drought tolerant than the commonly seen species described above. Funnel-shaped flowers of this plant bloom year-round when the soil is given occasional water, although this plant can subsist on winter rain alone. All Ruellias are powerfully magnetic to butterflies and hummingbirds. I checked the native plant nurseries in our area and was unable to locate Ruellia californica. Perhaps it is overlooked since its habitat does not cross the border from Baja California Sur (south) into Baja California Norte (north), the latter being part of the California Floristic Province. In any case, if anyone knows of a local source for Ruellia californica or the closely related and larger-flowered Ruellia peninsularis, please advise.

Please send questions and comments to joshua@perfectplants.com.