Most folks that are looking to buy a shamrock are really in the market for the oxalis plant. Oxalis is grown from tiny bulbuls, which rapidly re-develop underground and continue to grow year after year, making it a perennial. Sometimes, if you get a hold of the wrong variety of oxalis; i.e. wood-sorrel, you may get an invasive plant that will take over your garden that would be almost impossible to kill. Try growing them in containers instead of planting them directly into the ground.
The varieties of oxalis that are usually sold around St. Patrick’s Day are normally safe and not so invasive. They usually have green or red foliage with white, pink or even yellow flowers. The leaves are clover-shaped and have been know to have not just four leaves, but as many as 18, according to the Guinness Book of World Records.
On rainy or cloudy days, or at night, the flowers close and the foliage will fold over to conserve moisture. Do not over-water! Allow your “shamrock” plant to dry out between waterings or it will surely rot. Many times it is common practice to simply ignore the oxalis for a long period of time and allow it to rest, then water it to get it going again.
Oxalis blossoms can be used to make tea by steeping over water and the leaves, in small amounts can be chewed for a refreshing, but sour taste. But too much of this plant ingested can be toxic and interfere with proper digestion and kidney function. My advice is to simply look at them and not to eat them in any form.