OXALIS: WOOD SORREL
Oxalis (Ox'alis) includes about 200 kinds of hardy and tender plants. Most of them are found wild in South Africa and tropical and subtropical America, but the group is widely distributed and has representatives in many parts of the world, including North America. They belong to the family Oxalidaceae. The name is from axys, acid, the leaves being acid to the taste.
Several of the hardy kinds are beautiful plants for the rock garden, one or two are showy enough for the flower border, and many are excellent window-garden and greenhouse plants. They are propagated by seeds sown in spring, by offsets, or by division at the beginning of their growing season (September for most).
The Wood Sorrel. Oxalis montana, the American Wood Sorrel, is a charming wild plant with green “Shamrock” leaves and white flowers veined with lilac. It is well worthy of a place in the garden. Being a woodland plant, it thrives best in cool half-shady situations, and makes a pretty ground covering under trees and among shrubs. It may also find a place in the rougher parts of the rock garden, though care must be taken that it does not get out of hand and become a tiresome weed. A perennial, it grows only 2-3 in. high and occurs as a native in cool, rich woods in North America.
Oxalis violacea is another native American kind that is worthy of a modest place in the rock garden and wild garden. It occurs naturally from Massachusetts to Florida and westward to the Rocky Mountains. It grows 3-6 in. tall and has rose-purple flowers in summer. Like O. montana, it thrives best in a woodsy soil in light shade.
Attractive Hardy Annuals. Oxalis corniculata is a hardy annual with creeping stems. It forms a pretty, fresh green carpet, very dwarf and close, and bears bright yellow flowers in summer. There is a handsome purple-leaved variety, O. corniculata rubra, in which the golden blossoms contrast very effectively with the dark foliage.
Both these plants, the green and the purple variety, spread rapidly, throwing their seeds far and wide; they should therefore be introduced into the garden, and especially the rock garden, with the utmost caution, for they soon become troublesome weeds.
For filling the crevices in flagstone paths from which they cannot escape and spread, these two little Wood Sorrels are extremely pretty and useful, especially when grown together to contrast with one another.
Oxalis valdiviensis is a handsome and easily grown annual from Chile, 6-9 in. tall, with fresh green clover-like foliage, and heads of goldenyellow flowers. It may be sown in the open in April to flower the same summer.
For Dry Places Under Trees. Oxalis rosea is a beautiful annual from southern Chile. It grows 6-9 in. tall, is fleshy-stemmed, has bright green leaves, and bears quantities of pale lilac-pink flowers all summer. The great value of this plant is that it will grow in the very driest places under trees where scarcely anything else will exist. The plant often mistakenly grown as O. rosea is O. rubra.
For the Rock Garden. Oxalis lobata, from Chile, is an extremely pretty plant for the rock garden where winters are not excessively cold. The bulblike roots should be planted in spring in the moraine or in very light, well-drained soil in full sun. In early summer a crop of small fresh green leaves will appear, but these soon die down and disappear. A second growth will come up in late summer, accompanied by the flowers, which are a rich golden-yellow. The height of the plant is 2-3 in.
A Most Beautiful Kind. Oxalis enneaphylla, a native of the Falkland Islands and the Strait of Magellan region, is the most beautiful of all rock-garden Wood Sorrels and one of the choicest of all rock-garden plants. The root system is a fleshy, scaly rhizome (rootlike stem) about the size of a hazelnut. The leaves, consisting of nine leaflets, more or less, are glaucous blue-green, are folded in such a way as to give a crinkled appearance, and are carried on pinkish, erect stems 3-4 in. high. The flowers are large for the size of the plant, being 1-11/2 in. across; they are trumpet-shaped and white, and of a lovely waxy appearance. They are deliciously fragrant with a scent of almonds. The plant flowers in May and June.
Oxalis enneaphylla is not easy to grow in most American gardens. It is most likely to thrive in the Pacific Northwest. For its best development it needs an especially cool, well-drained loam with plenty of leaf mold added. A fairly cool, well-drained position should be chosen, shaded from full sun during the hot hours of the day. The plant is very lovely when grown in a pan of the soil recommended, in the alpine house.
Propagation of O. enneaphylla is carried out by breaking up the roots, which form themselves into strings of bulblike, scaly masses. The best time to do this is in spring, just as the plant, which is deciduous, begins to show signs of growth. The whole mass should be lifted, split up at every joint, and replanted at once.
Seed is sometimes obtainable, and this should be sown as socki after gathering as possible, in a pot of sandy loam and leaf mold, and kept shaded in a cold frame. Germination may be slow, and the pot should not be discarded under eighteen months or two years.
Oxalis ennecDhvlla was formerly used in the Falkland Islands for making a cooling, refreshing drink, and this was popular among sailors as a cure for scurvy in the old sailing-ship days.
There is a very beautiful variety, O. enneaphylla rosea, with pale pink flowers, which is a charming companion for the white-flowered type.
Oxalis adenophylla, from the Chilean Andes, is an extremely beautiful rock-garden plant, the leaves and flowers of which much resemble those of O. enneaphylla. The leaves are rather larger, however, but of the same attractive blue-green shade. The numerous large, trumpet-shaped flowers, each carried erect and singly on a 2-3 in. stem, are pale pink, with a crimson spot at the base of each petal. Although so beautiful, the flowers lack the fine waxlike quality and generous rounded petals of the best forms of O. enneaphylla rosea.
The root consists of a large globular bulb composed of innumerable narrow, scaly segments, and it differs from that of O. enneaphylla in making a number of side offsets around the base of the main bulb, instead of making necklace-like strings of bulbs.
Oxalis adenophylla is hardy perhaps as far north as Philadelphia bilt it is difficult to grow except in the Pacific Northwest. It needs a light, well-drained soil, in a sunny position in the rock garden. It flowers in early summer, and loses its leaves and becomes dormant in winter. It is easily propagated by division of the bulbs in spring, an operation which may be performed every three or four years.
For a Flagstone Path. Oxalis magellanica is a charming perennial, of close, creeping habit. Only half an inch tall, it has comparatively large, cup-shaped, pure white flowers. It is valuable for clothing the crevices in flagstone paths and as cover for choice small bulbous flowers in the rock garden, but, unfortunately, is not hardy in regions of severe winters. It is easily propagated by simple division of the plant in spring. The root system is creeping and wiry.
Tender Tuberous Kinds of Oxalis
Tender kinds of Oxalis that are not hardy in the North can be grown outdoors in mild regions; many kinds are also splendid for growing in greenhouses and in window gardens. They fall into two groups: those that have bulbs or tubers, and the nontuberous kinds.
When grown indoors, the tuberous kinds thrive in a light, well-drained, nourishing soil in full sun. They need a minimum night temperature of 45-50 degrees. The tubers should be planted at the beginning of their growing season, right at the end of their season of rest. This time varies according to kind, but, in general, spring-blooming kinds are started into growth in fall, summer-blooming kinds in spring, and fallblooming kinds in July or August.
The tubers (bulbs) may be set 6-9 together in a 6-in. flower pan, or slightly fewer in a 5-in. flower pot. They should be covered with soil to a depth of about 1 in.
Watering at first must be sparing, but, as leaves develop and the roots take possession of the soil, may be done more freely; when the plants are in active growth, weekly applications of dilute liquid fertilizer are in order. When the leaves begin to die down naturally after the flowering season is through, watering is gradually reduced and finally stopped altogether. The bulbs are then kept quite dry until the beginning of the next growing season.
During this season of rest the bulbs may be left in the soil or removed and stored in paper bags or other suitable containers in a fairly cool, dry place. Each year the bulbs are repotted in fresh soil at the beginning of the new growing season. At that time, propagation is readily effected by the natural increase of offsets.
These tuberous kinds are also readily raised from seeds sown at the beginning of the growing season of the particular kind. The seeds should be sown in pots or pans of light sandy soil in a cool greenhouse or in the window.
Among the best of these tuberous kinds is O. Bowieana, a South African kind that grows 612 in. tall and has large flowers. Bulbs of this Oxalis, planted in spring, produce flowers in late summer; bulbs planted in fall flower late in winter and spring.
Oxalis cernua, called Bermuda Buttercup, is 9-10 in. tall and has bright yellow flowers. It blooms in spring and is a splendid window-garden plant. O. cernua variety flore-pleno is a beautiful double-flowered kind; O. Deppei, 6-10 in., has red or purplish flowers in spring; O. brasiliensis, 3-6 in., has reddish flowers in spring.
O. hirta differs from most tuberous kinds in that it has erect, leafy stems. These grow to a height of 12 in. The plant bears pink flowers in fall and early winter. O. incarnata grows 6-10 in. tall and has purplish or lavender and yellow flowers in spring. O. lasiandra, 12 in. tall, has purple-crimson flowers in summer. O. lobata is a yellow-flowered kind that blooms in fall and is 3-4 in. tall. O. Bowieana (purpurea), a summer bloomer that attains a height of 6-12 in., has pink, purple or purplish-red flowers.
Oxalis variabilis blooms in late fall and early winter and has large flowers of pink, lavenderpink and red coloring. The plants grow 9-12 in. tall. This is the kind often sold under the name “Grand Duchess” Oxalis.
Nontuberous Tender Kinds of Oxalis
Easy to Grow. Among the nontuberous tender kinds are a number suitable for the greenhouse and window garden. Of these, O. rubra, a native of Brazil, is one of the easiest to grow and is one of the commonest. It is often misnamed O. rosea in cultivation.
O. rubra is a very free-blooming and attractive plant suitable for cultivation in a sunny, frostproof greenhouse and outdoors in mild climates. It is in full beauty in spring and summer. The roots should be potted in January or February. During the season of active growth generous supplies of water are needed. When the leaves have died down, the soil is allowed to become dry.
This kind bears satiny, bright pink flowers over a very long season of bloom. There is a white-flowered variety named O. rubra alba.
Three Shrubby Kinds. Oxalis gigantea is a most interesting plant from northern Chile. It makes an erect shrub up to 6-8 ft. tall, whose woody branches are clothed thickly with short spurs from which come tufts of rather fleshy, trifoliate leaves and numerous bright yellow flowers.
The plant is deciduous, and, when in flower, with the branches wreathed from top to bottom with masses of golden blossom, is extremely handsome. It is best propagated from seeds sown under glass in spring or early summer, and it is a plant for the cool greenhouses. It is rare.
More common in the United States is another somewhat shrubby Oxalis, O. Ortgiesii. This native of the Andes of Peru grows to a height of 1 1/2 ft., and has leaves that are rich purple beneath, and small yellow flowers. It needs no season of complete rest and thrives in a rather woodsy soil in a moist atmosphere, with a night minimum temperature of 55 degrees. It needs approximately the same conditions as fibrousrooted Begonias. It is propagated by cuttings.
O. hedysaroides rubra, a native of Colombia and Brazil, needs similar culture. Sometimes called Firefern, it has slender, erect stems, winered foliage and yellow flowers.
A True Shrub. O. dispar is a true shrub, and thrives in a moist atmosphere in a warm, tropical greenhouse. This native of Guiana grows slowly and branches freely. It needs the same conditions as O. Ortgiesii for its successful cultivation. It is propagated by cuttings.