for St. Patrick's Day
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
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.
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.