purple oxalis blossoms
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Barbara Pleasant:

 Indoor-Outdoor Oxalis

 
oxalis leaves
The St. Patrick’s Day Shamrock

The real Irish shamrock plant is a clover relative (Trifolium dubium) which prefers the wild life to domestication. The adaptable oxalis has taken its place, and is often sold as a good luck shamrock plant for St. Patrick’s Day. Leaf colors vary, with green, bicolored, and purple shamrocks available at very good prices. Purple shamrock plants make great color accents for shady decks or patios.  

repotting oxalis
red oxalis in bloom
After a winter rest, red oxalis are up and blooming in early spring, while the trees outdoors are still bare.
purple shamrock with cat
Miss Ella
Thanks to April G. for pointing out that oxalis can be poisonous to pets. The leaves taste extremely sour due to their high oxalic acid content, but some pets eat them anyway. If you notice pet grazing on your shamrock plant, immediately move it to where your animals cannot reach it. Miss Ella would never consider eating anything that is not in her food bowl, unless it's a bug.
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Oxalis groundcover

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To learn more about pretty prayer plants (red marantas), see my Maranta information page for tips and trivia.
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Charmed Wine oxalis
'Charmed Wine' oxalis from Proven Winners

If you want an easy houseplant that produces plenty of pretty flowers and lots of drama, oxalis, commonly called shamrock plant, should be on your list. Oxalis in any color can't wait to start blooming in late winter. Purple shamrocks have pinkish flowers, with white flowers more common on green shamrocks. Happy plants will bloom intermittently year round.

That is, unless you forget to water a plant and it collapses and then shrivels up. This is the drama part. You think your purple shamrock is dead, so you stash it in an out-of-the way place, maybe on its way to the trash can, and forget about it. Then fate intervenes, somehow fills the container with moisture, and your lost darlings arise from the dead!

They were merely resting on their pips, you see.

Native to South America and Africa (there are several species), oxalis plants seem to relish a period of dormancy of at least 4 to 6 weeks, whether intentional or accidental. A good parch will send them into a resting mode, as will shearing back all the leaves.  I once did this as a spider mite intervention. After the plants enjoyed a dry rest, and the new leaves came on totally clean.

Repotting Oxalis

To start on the same page as my dear readers, this spring I bought a new purple oxalis at the supermarket. It needed repotting in early June, so I moved it from its plastic nursery pot to a 6-inch terra cotta pot. By August it the plant had grown so much that I couldn’t keep it watered, and I had to decide whether to pot it up one more time or let it become dormant. I opted to move her up to an 8-inch pot and let her grow and bloom until the first of November. Then I’ll let my repotted oxalis dry down and rest in the cool basement through January, ready to awaken on February 1 with warmth, water and light. By St. Patrick’s Day she’ll be in full bloom.

Sharing Shamrocks

I like to repot crowded plants in late winter -- prime sharing season for shamrocks. Even if all the leaves disappear from a pip that is actively growing, new ones will emerge within days. I have even seen oxalis roots sold in little bags, so they are pretty darn tough.

Oxalis rhizomes
Oxalis rhizomes
Recently I received an inquiry asking how to orient the roots when repotting oxalis. Horizontal is good, or you can angle the roots diagonally, so that the end with the most buds is higher than the end with roots.

I use extra purple oxalis as accent plants in summer deck containers, and sometimes as summer groundcover plants in flowerbeds. The plants don’t survive winter in Zone 6, but  in warmer climes oxalis can quickly become a weed. Purple oxalis as well as red-and-green iron cross strains are hardy only to Zone 7, but several species can survive much colder winters.  Species that do not make tubers (for example, O. vulcanicola) are especially bad about throwing seeds where they are not wanted.