Nierembergia

These are hardy and tender, perennial plants that may be dwarf or trailing and are good for the rock garden, or are taller and erect and make good plants for the flower bed or border. All can be grown in pots. These plants come from South America. They form tidy mounds, up to 12 inches high/wide. Their leaves are linear and up to an inch long. The flowers are shaped like shallow cups, 1 to 2 inches across. They may be blue, violet, lilac, or white. They are produced singly on the ends of thin side branches. N. rivularis, which grows about 3 inches high, forms a carpet of green foliage and creamy white flowers streaked with purple.

Pot Cultivation

Hardy kinds can be planted outdoors in the spring, in a sunny, moist position in the rock garden. The soil should consist of equal parts of loam and leaf mold. During the summer, the soil must be kept moist. Tender kinds can be grown in greenhouses in the North or they may be planted outside during the summer. In mild climates, they may be grown outdoors all year as perennials. In the fall, the plants can be lifted from the soil, pruned back, potted and kept in a cold frame or greenhouse during the winter. N. frutescens is a great summer-flowering plant for the greenhouse; it produces light blue flowers. If grown in the greenhouse, it should be planted in 5- or 6-inch pots filled with loam, leaf mold and sand.

Propagation

Seeds may be sown indoors at 70 to 75 degrees, 8 to 12 weeks before warm weather, in pots of sandy soil. They may be potted outdoors or kept in 5-inch pots for the greenhouse or window garden; they should be planted in a compost of sandy loam, some well-decayed manure and a bit of sand at the final potting. Water carefully until they are well established. When they've finished blooming, less water is needed and throughout the winter, the soil is moistened only when it's moderately dry. Cuttings of shoots, 2 inches long, are removed, the lower leaves are taken off and a cut is made just below the bottom node. They are then inserted in sand or vermiculite in a greenhouse propagating bench.