Shamrocks for St. Patrick's Day 

The "Shamrock" is a common gift plant for St. Patrick's Day, whether you're Irish or not. Officially, the shamrock is a yellow-flowered clover or trefoil (Trifolium dubium), the national emblem of Ireland. But these clovers are difficult to grow indoors, so nurseries and florists often substitute the common three-leafed Oxalis as a potted remembrance of Ireland's patron Saint on March 17. These little pots of green are a fine tribute to St. Patrick and can be kept as a houseplant long after the celebrations have ended. 
he common Oxalis is a member of the Wood Sorrel family of plants (Oxalidaceae) which contains over 300 species. Most of the species grow from small bulbs but some are produced from tuberous roots and others arise form creeping root stalks. Most Oxalis have three, sour-tasting, rounded, green leaves which grow at the end of delicate stems. Some Oxalis, however, have triangular-shaped leaves or leaves with various tinges of purple or brown. One particularly handsome species has deep red leaves, each marked with a dark line across the center. Whatever the number or whatever their color and shape, most Oxalis plants fold their leaves up at night, hugging them tight to the stems until the next day's dawning light draws them out to their full spread again. 

Oxalis have flowers that may be white, pink or purple, yellow or red. Oxalis purpurea, the Cape Oxalis is commonly used as a houseplant and has white flowers. Another white-flowered species, Oxalis regnellii, has triangular shaped leaves that are green on top and purple underneath and grow from a tuberous root. Oxalis stricta, and Oxalis corniculata are both weedy species of Oxalis that have small yellow flowers. These plants occur in fields or along roadsides throughout the Maritimes and can invade home gardens where they grow quickly and tend to choke out crops and ornamentals. Oxalis deppei is a red flowered Oxalis native to Mexico. Oxalis rubra, the window box Oxalis, has pink flowers. This species is native to Brazil but is often grown as a houseplant in northern climates because it flowers so well throughout the winter months. 

Plant Care: 

Oxalis grow best in full sun. They should be kept uniformly moist, in humid conditions, well away from drafty locations. If the plant dries out or is exposed to dry air or cold drafts, it will soon lose leaves and will be slow to produce daughter bulbs or flowers. If the plant is kept too wet, the bulbs or tubers will rot. 

Oxalis plants do not have extensive root systems and thrive when they are crowded in a pot. However, if a plant seems to dry out too quickly it may be necessary to move it to a new pot that is just one size larger than the old one. To remove an Oxalis from its crowded home, hold the leaves together with one hand while inverting the pot and gently tapping its rim against the edge of a table or cupboard with the other hand. This process should allow the root ball of the plant to slide out of the pot intact. While the leaves are still held together (to keep them from being broken or buried during the repotting process) center the root ball in the new, larger pot that has already a small amount of standard potting mix placed over its bottom. Add potting mix between the root ball and side of the pot and then gently tamp it in place. It is important that the tiny root hairs on the outside of the root ball be damaged as little as possible during the repotting process. Stop adding new potting mix when it is flush with what was the potting mix surface in the old pot. If the root system is buried deeper than it was before the plant may begin to rot at the base of the leaves. 

The plant should be watered well after repotting to allow the new potting mix to settle in around the root ball. While the plant is actively growing or flowering it should be fertilized every 2 to 3 weeks with a standard houseplant fertilizer according to package directions. 

Although many Oxalis will grow continuously, some species require a rest period after they finish flowering. If the plant begins to develop yellow leaves and an overall sickly appearance after it stops blooming, it will be necessary to gradually slow down on watering until all of the foliage has died back. The plant should then be stored in a cool, dark place for several weeks while it goes through its dormancy period. The appearance of new green shoot tips at the surface of the potting mix (from the tiny bulbs of the dormant plant) will indicate that the rest period is over and normal growing conditions should be resumed.