Oxalis, a natural for containers
With the popularity of container gardening exploding, the hunt for suitable pot plants has become intense. Gardeners are demanding container plants that bloom for most of the growing season and have attractive foliage all season. Oxalis is one pot plant that should meet their requirements.
Oxalis (of the Oxalidacae family), native to South Africa and the Americas, are tender perennials with clover-like leaves that may grow from bulbs or rhizomes, or simply have fibrous roots. The dainty flowers are borne in small clusters on slender stalks held slightly above the compound leaves. The flowers can be red, various shades of pink and coral, lavender, purple, or yellow.
While oxalis is often compared to clover, its foliage is different in that all the leaflets on the compound leaves are the same size. They are usually either trifoliate or have four leaflets on each petiole, and each leaflet is symmetrical and somewhat heart-shaped. It is the remarkably distinctive and attractive foliage that makes oxalis such a good container plant.
Because they are, in the main, native to warm, and often hot, climates, oxalis are not hardy in most Canadian gardens and must be treated as annuals, or over-wintered indoors.
Although there is an oxalis, the purple- leafed, white-to-pink-flowered Oxalis triangularis, that is used as a house plantas well as a garden adornment, the foliage of other oxalis will gradually become etiolated unless given a bright place indoors. Grown outdoors in full sun or part shade, oxalis foliage maintains its deep, attractive colour all season. (Some older leaves turn yellow and should be removed to improve the plant’s appearance and to increase the air movement among the remaining tightly packed foliage.)
One of the best oxalis is O. tetraphylla ‘Iron Cross’, sometimes listed as O. Deppei. This oxalis has large leaves, up to nine cm in diameter, four leaflets per stem,. These are mid green with dark burgundy centres. The blooms are a rich coral and held well above the foliage to produce maximum impact. The plants bloom prodigiously in spring and early summer and then intermittently for the rest of the growing season. The plants grow from small bulbs and when these are planted thickly enough in a large pot, the resulting container can be stunning.
‘Charmed Wine’ is a popular, award-winning shamrock in the Charmed series which can adorn landscapes as well as hanging baskets and window boxes. It has violet leaves and delicate looking pink flowers, and is enticing as a shade plant, or in semishade. At 30 to 45 cm high it can be used as middle-ground in a container arrangement, from where it mixes happily with the other plantings. Oxalis vulcanicola ‘Zinfandel’, another award winner, is in contrast a sun lover, though it also thrives in partial shade. A shorter, mounded plant, with purply-black foliage and yellow flowers, it will happily fill in the middle ground in a container planting, mingling well with its neighbours.
Not all oxalis have four leaflets per stem. One attractive trifoliate variety is O. occidentalis, whose pure green leaves are much more triangular in shape than those of O.tetraphylla. Also grown from bulbs, it forms a dense, bushy potful of foliage, above which appear stems of deep lavender blooms. This variety tends to bloom throughout the summer and lacks the initial burst of bloom of ‘Iron Cross’.
Oxalis that are grown from bulbs require lots of water; they wilt if the soil is allowed to dry out. They will sometimes wilt during the hottest part of a hot summer day and it’s therefore best to protect them from strong midday sun. They are also heavy feeders and should be planted in a well-drained planting medium to which some soil or compost has been added. During the growing season they require regular applications of fertilizer or their foliage will etiolate.
In the fall, if the plant is not being overwintered in a bright indoor location, pots of oxalis bulbs can be allowed to dry off by withholding water. The pots should be moved inside before there is a danger that the bulbs will freeze, although the foliage can be exposed to frost as that will hasten its drying off. The pots with their bulbs can then be stored in a cool, dark location for the winter.
In early March the pots can be brought out of storage and watered. New growth will soon appear at which time the plants should be placed in strong direct light. By mid-May, when they are put outside, they will already be in bud. If the bulbs have been potted for a couple of years, they should be dumped out of their pots in the spring and the bulbs collected. They can be replanted, about three cm apart in new potting mix, and given water and good direct light to encourage growth.
Stunningly beautiful foliage, easy care, the capacity to be used year after year and beautiful, dainty bloom – what more could a gardener ask from a plant? Oxalis are showing up on more and more gardeners’ plant lists, and with good reason.
Albert Parsons is a garden columnist living in Minnedosa.