Oxalis: A great plant indoors and out
Oxalis – often called shamrock – has beautiful foliage and plenty of dainty blossoms. Plus, it's easy to care for indoors and out.
The middle of March is always about shamrocks, those defining symbols of St. Paddy’s Day. Of course, if truth be told, what we here in the US call the shamrock isn’t the same plant as the shamrocks of the Emerald Isle.
In Ireland, the shamrock is represented by four different clovers, the two principal ones being the hop clover or lesser trefoil (Trifolium dubium) and the white-flowered clover (Trifolium repens). These three-sided clovers have long been part of Irish folklore and are commonly associated with good luck.
The Americanized version, the four-leafed Oxalis tetraphylla (lucky clover), on the other hand, is the nifty clover look-alike usually found in gift shops, grocery stores, and garden centers during the month of March.
The plant has green leaves with dark burgundy markings and pinkish-red blooms that are displayed profusely in spring and early summer, then intermittently for the remainder of the season. Planted out in containers, the effect is awesome.
Oxalis run the gamut from rampaging weeds – Oxalis corniculatam, O. stricta, and O. pes-caprae – that inhabit American lawns and greenhouses to fabulous, (but not hardy in cold climates) rock-garden plants and edgers.
Although most are not hardy enough to remain outside in my Midwest garden, there are a few exceptions, such as the diminutive rose-pink flowered stunner, Oxalis inops (Oxalis depressa) and the short but showy pink-flowered wood sorrel, Oxalis crassipes (strawberry oxalis) – a staple of Southern cottage gardens – which are reliably hardy to Zones 5 and 6.
These bulbous plants have frost-tender cousins that provide dainty flowers in various shades of pink, lavender, purple, yellow, or white and colorful foliage from spring until fall in pots or as summer annuals planted out in the ground.
Most produce mounds of attractive, shamrock-shaped leaflets, four to 12 inches tall, with a profusion of 1- to 2-inch blooms.
The leaves of oxalis can be bright green, deep purple, and maroon, or even interesting combinations of these colors. A few newer introductions sport light chartreuse leaves, as well as green leaves that are dotted, speckled, and splashed with silver.
Oxalis thrive in part shade, preferring well-drained soil that is kept evenly moist, but not wet.
In contrast, one attractive cultivar, Oxalis vulcanicola ‘Zinfandel’, which has purplish-black foliage and yellow flowers, is, in fact, a sun worshipper, although it also does just fine in partial shade.
Oxalis plants relish lots of water, and will wilt if the soil is allowed to dry out. They will also sometimes wilt during the hottest part of a summer’s afternoon, so it’s best to protect them from exposure to strong sunlight.
One rather charming trait of the plant is that the leaves are capable of movement, folding down at sunset, when drought-stressed, or in heavy rain.
They are heavy feeders, so when they're in active growth, fertilize at half strength with a liquid fertilizer for flowering plants (such as 15-30-15).
This is my first year growing oxalis, so I’m still in the “trial and error” stage. Late last summer, I purchased ‘Wine’ and ‘Velvet’ from the award-winning Charmed series of oxalis plants because I was intrigued by the dark purple, almost black foliage of the plants.
My friend Marietta is into plants with black foliage, and her enthusiasm for the dark side is catching, I've found.
If you have the room, oxalis can be brought insideto a right location to overwinter as a house plant. Or, you can do as I did --- bring the container-grown plants inside, hold back on watering, and overwinter them in a cool, dark place in an unheated basement.
April 1, I’ll move the containers to a plant stand under lights, water them, and, if all goes well and according to plan, the cycle should start all over again.
Betty Earl is one of nine garden writers who blog regularly at Diggin' It. She's the author of “In Search of Great Plants: The Insider’s Guide to the Best Plants in the Midwest.” She also writes a regular column for Chicagoland Gardening Magazine and The Kankakee Journal and numerous articles for Small Gardens Magazine, American Nurseryman, Nature’s Garden, and Midwest Living Magazine, as well as other national magazines. She is a garden scout for Better Homes and Gardens and a regional representative for The Garden Conservancy.
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