Luck O' the Irish! Shamrocks rock

Posted by: Alison O'Connor, Larimer County Extension

Don't let the last name fool you...I'm German and Swedish, but on St. Patrick's Day, everyone can be Irish! And we should take the time to celebrate our clover friend, the shamrock.

Shamrocks are a member of the Oxalis family, also known as wood sorrels. The family contains over 300 species of plants, most of which grow from bulbs, though some have tuberous roots. A distinguishing characteristic of the shamrock is how it folds up its leaves at night, “hugging” the stem. The leaves re-open at daylight. The familiar plant grown for St. Patrick’s Day is Oxalis acetosella. This plant has small, dark green, triangular leaves and usually grows no more than six inches tall. Though it’s not the official shamrock of Ireland (Trifolium dubium), it’s much easier to grow indoors.

Shamrocks (Oxalis acetosella)

Why is the shamrock associated with Irish history? The most popular reasoning is because of Saint Patrick, who is credited for bringing Christianity to Ireland. History claims that in front of his congregation, he picked a shamrock from the grass at his feet to demonstrate the doctrine of the Holy Trinity. St. Patrick’s Day is celebrated on the anniversary of his death and it also symbolizes the arrival of spring. Thus, the shamrock was adopted to pay homage to Saint Patrick and announce the “season of rebirth.”

A stained glass depiction of Saint Patrick
(Photo from Wickipedia.com)

Growing shamrocks indoors takes a bit of patience and practice, meaning I will never grow them. The plants like cool, moist soil and bright light, except when they are dormant. Daytime temperatures should be no more than 75 degrees, and 50 - 65 degrees at night. They do not have an extensive root system and prefer to be pot-bound. Fertilize shamrocks every two to three weeks while it’s actively growing or flowering. Oxalis plants can become leggy if there isn’t enough light, or if temperatures are too warm. If the plant begins to look “sick” and starts to lose its leaves, don’t worry—it’s going into dormancy, which happens two or three times per year. While the plant is dormant, stop watering and let the foliage die back naturally. Shamrocks “rest” for about three months, then will send up new green shoots. When the shoots emerge, move the plant back into the light and water regularly. Oxalis flowers can be white, pink, yellow, purple or red, and some varieties can reach 10 inches tall. Leaf color ranges from dark green to a deep red.

Shamrock flowers

Another oxalis you may be familiar with is the lawn weed, Oxalis stricta, also known as yellow woodsorrel. This “shamrock” has perfectly heart-shaped leaves and yellow flowers. It’s an incredibly difficult weed to control in home lawns and landscapes. It prefers low cut turf that is well-watered. To address this weed, first raise your mowing height and reduce irrigation inputs. Once the turf is healthy, oxalis will disappear. If you need herbicide assistance, select products containing triclopyr (for example: Ortho Weed-B-Gon Chickweed, Clover and Oxalis Killer). Apply according to the directions on the label.  

Yellow woodsorrel or oxalis growing in a lawn
(Photo from the University of Minnesota)

Personally, I think sticking to the "tried and true" holiday plants are much nicer than the weird ones they dye. Why do they do this?

Isn't a simple white orchid more attractive than these sickly green dyed ones?