Apparently, this native of Brazil only came into the horticultural trade in the 1980s. I love it because it falls into the easy and carefree category — that is if you keep it protected from freezing over the winter. It is actually a small tuber sold as a summer bulb, which in our climate won’t survive the winter in the ground.
Overwintering means ignoring about them until mid-April. I don’t even water the pots: the little tubers keep very nicely in the dried-up potting soil.
In very early spring, I dump the contents of the containers into a wheelbarrow and begin to divide all of the tubers from the previous season — they multiply prodigiously.The ones that will go into the ground as edging plants, I start in deep 4-inch pots. Each pot gets fresh potting soil and a handful of tubers, and then water. (Since it’s hard to tell which end is up, I don’t worry about that and just dump them in.) I also divide the tubers destined for container-growing, setting them 2 to 3 inches deep into large terra-cotta pots where they spend the summer.
I put the pots of Oxalis outside in the sun, making sure to cover them or take them inside the garage if frost is forecast. When the leaves emerge — that takes a few weeks — I move them to a shadier spot and give them diluted all-purpose liquid fertilizer (20-20-20 about half strength).Once the plants are growing vigorously and all danger of frost is past, Oxalis can be planted in the ground like any other annual. Over the season, I water them regularly and give them fertilizer maybe once a month.
They thrive in light or deep shade, and do well even in dry shade. They will also grow in sun, although the purple color of their leaves can fade and turn a bit muddy in too-bright conditions.
The tubular flowers are a delicate light pink and continue producing blooms all summer. They are self-cleaning too – you never need to deadhead, a real bonus in my book. A lovely annual staple — as long as I have a garden, I’ll keep my Oxalis going. Every last one comes from that single gift pot which started this plant love affair.
Do you have a favorite summer bulb or annual plant that you wouldn’t be without?
You can buy Oxalis Triangularis (Purple Shamrock) here (American link). Canadian bulb suppliers and garden centres usually carry it in the spring.
Featured comment: From Dave Cummins who gave me my starter Oxalis plants: “The Oxalis is still a mainstay in my garden as well for the many reasons you mention in your blog. I am probably responsible for a wide distribution of the plants in those past 15 years. One evening in July this year a deer paid us a visit and totally devoured both flowers and foliage from the Oxalis that I had in a large cement planter. Within 10 days the plants totally rejuvenated themselves and probably looked even better then they did prior to the deer attack. Thanks for the mention in your blog.”