PLANTS of the genus Streptocarpus (cape primrose) are of two types: stemless and stemmed. The stemless kinds are more common as house plants, because they have given rise to many attractive, profusely flowering hybrids. Some of the stemless kinds are unique in that they form only one big leaf, and die after flowering. Because the leaf can grow inconveniently large, single-leaf streptocar-puses are rarely grown indoors. Other stemless types are longer-lasting. Some have smaller leaves growing from the base of a large leaf. Others have several leaves of the same size arranged in rosette form. The popular hybrids belong to this last group. In all the stemless types the leaves are stalk-less. Flower stalks rising from near the bottom of the midrib of each leaf carry small clusters of flowers. In the stemmed streptocarpuses the much-branching stems bear leaves in opposite or alternate pairs or in whorls of three or four, and the flower stalks rise from leaf axils. Some species have several flowers on each stalk, and others have only one per stalk. The flowers of all streptocarpuses have a tiny, five-lobed calyx backing a tubular corolla that flares out into a five-lobed mouth. Flowers are followed by spirally twisted, frequently attractive seed pods. To promote flowering of the hybrids, however, pods should be removed as they form.
S. 'Constant Nymph,' the most popular hybrid, is a rosette-forming plant with medium to dark green, strap-shaped leaves up to 12 inches long and 2 1/2 inches wide. Several 6-inch-long flower stalks grow from each midrib base, and each stalk bears two to six flowers up to 1^ inches long and 2 inches across. Flower color is blue with dark blue lines running from the lower lobes of the corolla into the pale yellow throat. Flowers bloom from spring to fall. S. 'John Innes' hybrids have leaves and flowers like those of S. 'Constant Nymph.' Flower stalks are up to 8 inches tall, and flower color ranges from pale pink to deep purple to blue. Corolla lobes of some forms have markings extending into the throat. These hybrids will flower all year long under the right conditions. S. polyanthus is mainly a single-leaved type, but some forms grow secondary leaves. The big, downy, slightly scallop-edged, medium green leaf can grow 12 inches long and 6 inches wide. The secondary leaves are similar but only 2 inches long and J inch wide. Up to a dozen 12-inch-tall flower stalks bear from 7 to 30 flowers each. The flowers are \\ inches long and across, yellow, with blue, tooth-edged lobes. The main flowering season is from spring to fall. S. rexii is a rosette-forming plant with oval, hairy, ruffled, slightly scallop-edged, medium green leaves up to 10 inches long and 4 inches wide. About four 6- to 8-inch-tall flower stalks, each with up to three flowers, are produced from each mature leaf. The 2-inch-long, 1 -inch-wide flowers are bluish mauve with violet lines running from the lower lobes into the throat of the corolla. Under the right conditions flowering is continuous. S. saxorum has branching stems up to 12 inches long, which tend to lean over sideways. Oval, velvety, gray-green leaves are arranged in opposite pairs or whorls of three at stem and branch tips. The 1-inch-long and 1-inch-wide leaves have turned-under margins and prominently veined, pale green undersides. Flower stalks 3 inches long carry solitary flowers 1 inch long and 15 inches across. The hairy, white corolla has a pale lilac mouth. Flowering time is spring and summer. S.'Wiesmoor' hybrids are rosette-forming plants with strap-shaped, medium green leaves up to 12 inches long and 3 inches wide. At least five stalks 6-15 inches long carry three or four flowers each. The 2-inch-long, 3-inch-wide flowers are markedly funnel-shaped, and the flared ends are fringed or ruffled. Flower color ranges from white through blue to dark red, often with dark markings on the lower lobes. The flowering season lasts from spring to fall.
Light Give actively growing plants bright light without direct sunlight. In the rest period, if any, medium light is adequate. 5. saxorum can tolerate medium light at all times.
Temperature All streptocarpuses will grow actively throughout the year in normally warm room temperatures. At temperatures above 75°F provide extra humidity by standing pots on trays of moist pebbles, and keep the roots cool by covering the surface of the potting mixture with a constantly moist layer of sphagnum moss. If indoor temperatures fall below about 550 for more than a day or two, all streptocarpuses (with the probable exception of S. saxorum) will have a rest period.
Watering Water moderately, allowing the top half-inch of the potting mixture to dry out between waterings. During any rest period, allow a full inch of the potting mixture to dry out between waterings.
Feeding Apply a high-phosphate liquid fertilizer at half strength every two weeks to actively growing plants.
Potting and repotting Use a potting mixture composed of equal parts of sphagnum peat moss, perlite, and vermiculite. For a well-aerated mixture the peat moss should be rough-textured and lumpy, and the perlite should be fairly coarse-grained. Add half a tablespoonful of lime chips to every cup of mixture. Use shallow pots or pans for these shallow-rooted plants, and move the plants into slightly larger containers only when roots fill the pot. Repotting is best done just after a heavy bout of flowering. Six-inch containers should be the largest required.
Propagation Except for S. saxorum, propagate in spring from leaf cuttings. Remove a leaf, and cut it across its width into two or three sections. Insert the base of each section J inch deep in a 2 ½ -inch pot of the mixture recommended for adult plants. Place the pots in medium light, and keep the mixture barely moist. Plantlets should appear at the bottom of the sections in four to six weeks. When a plantlet is 2-3 inches tall, pull it away from the parent section, plant it in a 2 1/2-inch pot, and treat it in the same way as a mature specimen.
Propagate S. saxorum from 2- to 3-inch-long tip cuttings taken in spring. Insert each cutting 1 inch deep in a 2-inch pot of moistened potting mixture, and place it in medium light. Water sparingly, enough to make the mixture barely moist throughout until new growth indicates that rooting has occurred. Thereafter, treat the rooted cutting as a mature plant.
Special points Mildew is a possibility if streptocarpuses are given high humidity without adequate air circulation. (Do not, however, subject the plants to cold drafts.) Watch out, too, for mealy bugs on leaf undersides.
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