Backyard Gardening

By Carol Lugg

Shamrocks are about to hit our local grocery stores and nurseries and provide an encouraging sign of spring for our windowsills. The bright pop of green offers a welcome relief to the grey days of winter as they usher in the beginning of the spring season, serving as a symbol of spring. The shamrock has a long history of symbolism, used for luck and good fortune. As a kid, I likely enjoyed my fair share of Lucky Charms with their magically delicious marshmallows. Every spring, in my small town Methodist church in northwest Ohio, Mrs. Beck, a stern, disciplined, but caring farm wife would keep us active farm kids in line with her expectations of good behavior during the Sunday School hour. A talented storyteller, Mrs. Beck would pull out a shamrock plant and remind us of the significance of each leaf and its role in serving as a representation of the Trinity, with the Father, Son, and the Holy Spirit, individually pointed out leaf by leaf and how they came from one stem. Meanwhile, my Catholic buddies across town were learning of St. Patrick and his power to drive snakes out of Ireland and his 5th century work at sharing the Holy Trinity with unbelievers, with the shamrock plant as the symbol. Historians are uncertain as to what plant St. Patrick used in his teaching, and at age seven, I didn’t think to ask Mrs. Beck to verify the genus of the plant she presented, but it was likely a shamrock. It may have been from the genus Trifolium or genus Oxilas. 

My efforts to research and write this article started out harmlessly enough. I thought I’d easily find the genus and species of the plant that is typically available in grocery markets to announce the arrival of St. Patrick’s Day. I’d then share how to care for the plant to extend the seasonal enjoyment. My research uncovered conflicting results regarding which plant is widely distributed to celebrate the Irish holiday. However, the research was consistent with the fact that the name shamrock originated from an Irish term (I was not surprised by this discovery), seamróg, meaning little or young clover. Clover plants, such as Irish shamrock (yellow clover), as well as a miniature form of white clover (Trifolium reopens), are found in the genus Trifolium (https://ipm.missouri.edu/MEG/2019/3/oxalis/index.cfm), which includes over 300 species.  Unfortunately, no unique species identified as shamrock originate from Ireland. 

The genus Oxalis includes over 550 species, including false shamrock, wood sorrels, and sourgrasses (https://plants.usda.gov/). Plants in this genus have species that carry the shamrock’s signature three-leafed stem, and the plants available for retail are likely from this genus (https://hort.extension.wisc.edu/articles/shamrocks-oxalis-spp/). The plant may be tagged Irish Shamrock, Oxalis acetosella, or wood sorrell. Oxalis may have green or purple leaves and, depending on the species, may have leaves with interesting patterns. One telltale sign of the genus Oxalis is that all species produce a flower with five petals on long stalks. The plant will enjoy a home where daytime temperatures will not exceed 75 degrees Fahrenheit and nighttime temperatures in the 50-65 degree range at night. Be sure to keep the soil moist but well-drained. Fertilize the plant while it is actively growing (https://planttalk.colostate.edu/topics/houseplants/1354-shamrocks-houseplants/). The plant will need bright light, typically found in a south-facing window. When the plant begins to die back, don’t toss it in the trash, but rather stop watering and place the plant in a cool, dark location. After a period of dormancy, typically lasting a few weeks to a few months (depending on the species), the plant will begin to send out new shoots. The plant will go through this cycle two, three, or more times yearly. When the plant is ready to reemerge, you can divide your tubers into several pots and enjoy them as outdoor or indoor plants (https://extension.psu.edu/the-botany-behind-the-shamrock), depending on the season. As the hardiness zone varies depending on the species, you will have to identify your plant before determining its cold hardiness. 

The Oxalis species have a bulb-life storage structure; the leaves will die down and go into a dormant stage for four to eight weeks. As the plant leaves begin to die, remove them and allow the plant to rest in a cool location. When the plant is ready to reemerge, you can divide your tubers or bulb-like structures (see photo) into several pots and enjoy them as outdoor or indoor plants (https://extension.psu.edu/the-botany-behind-the-shamrock), depending on the season. The plants like to be snug in their pots, so be sure to err on the small size when selecting a container. After a period of dormancy, the indoor plant should be watered and moved back into bright light. This past summer, I planted the Oxalis regnelii or Purple-Leaf Shamrock (see photo) in my window boxes on the north side of my house. When the plant died down, I removed the spent leaves, and within a few weeks, the plant emerged again, showing off its purple foliage that contrasted nicely with my green ferns. This species had white flowers that provided a nice show and a unique and creative option to the impatience that typically filled that area. This species has purple leaves with darker borders, making for an interesting foliage display. I also enjoyed experimenting with Oxalis deppei, commonly known as Lucky Clover or Iron Cross. This species has green leaves with purple centers and may be available for purchase as a “shamrock” plant during the seasonal push of shamrocks in March. 

If the color isn’t interesting enough, Oxalis provide additional interest to your garden as the plants are nyctinastic. Gardeners may be familiar with this process as the popular house plant called the prayer plant, Marantaceae, also exhibits nyctinasty. Ncytinasty is when a plant’s leaves close up at night and reopen in the day. Cloudy days will also spur the plant into this behavior. 

During the long days of March, try your luck with different species of Oxalis as indoor plants and consider how you might use them in your summer garden. While the folks in Ireland are split over whether the species Trifolium dubium (lesser clover) or Trifolium repens (white clover) is the shamrock (https://ucanr.edu/sites/glennmg/files/211379.pdf), the shamrock plant you bring home for your celebration will likely come from the genus Oxalis. What does matter is that you enjoy the plant you bring home and rather than tossing it, experiment with allowing the plant to go through its dormant state and see, with a bit of luck, if your plant reemerges with another flush of growth. I think Mrs. Beck and St. Patrick would both be proud of your faith in the lifecycle of the botanical world. 

Carol Lugg became a Penn State Extension Master Gardener in March 2022. She can be reached at clintonmg@psu.edu or the Clinton County Master Gardener Hotline at (570) 858-0198.