• Topics: Environmental Horticulture  |  House Plants  |  African Violets  |  Gesneriaceae (taxonomic family) 

Gesneriads for the Florida Gardener¹

Florida's plant enthusiasts should become well acquainted with the Gesneriaceae, a family which includes some of the most popular hanging basket and flowering pot plants. Virtually all gardeners are familiar with two gesneriads, African violets and gloxinias, but few are aware of the many other species and hybrids which make excellent flowering pot or hanging basket plants and dish garden and terrarium subjects. The appeal of gesneriads lies not only in their abundant, colorful flowers, but also in their attractive and colorful foliage, desirable growth characteristics, and relative ease of culture and propagation. As a group, gesneriads are long-lived, robust plants which flower profusely under Florida's climatic conditions. By obtaining healthy, vigorous plants from retail outlets or specialty nurseries and following the suggestions outlined below, Florida's gardeners should be successful at growing gesneriads.

CHOOSING GESNERIADS

A good way to choose a gesneriad is to first determine how the plant is to be grown, whether as a hanging basket, a pot plant, or as a terrarium or dish garden subject; then select a gesneriad which is suited for the particular effect.

Achimenes (Magic Flower) are popular hanging basket and pot specimens producing large (one to two inches in diameter) colorful flowers during summer. Flower colors include red, pink, yellow, lavender, violet, and blue, ranging from intense hues to pastels. Varieties with white flowers, white with colored venation, or colored with white throat are very attractive.

Aeschynanthus species and hybrids (Lipstick Plants) are ornamental trailing plants best grown in hanging baskets. Brilliant red, orange, yellow, and combinations of these are found in tubular flowers produced in abundance in spring and summer. The emerging red flower buds and tubular calyx of A. radicans and A. pulcher resemble a lipstick, hence the common name, Lipstick Plant. Aeschynanthus marmoratus, with maroon venation marking glossy green leaves, makes attractive foliage in hanging baskets.

Codonanthe and Nematanthus have excellent potential as hanging basket specimens in Florida. In Codonanthe, tubular white flowers project outward from succulent glossy green leaves suspended below the hanging container. Orange, pink, or white marble-sized berries follow the flowers, prolonging the show of color. Nematanthus varieties are trailing or semi-erect plants noted for their brightly colored, pouch-shaped flowers and free flowering habit.

Columneas produce some of the most magnificent flowering hanging baskets in the Gesneriaceae family. Columneas are trailing or semi-erect plants with brilliant yellow, orange, red, pink, or combination colored tubular flowers several inches in length and up to one inch across. Flowers develop year round in the axils of leaves and project away from the foliage.

Episcias are favorite hanging basket and terrarium plants valued especially for their attractive, often multicolored foliage and colorful funnel-form flowers. Leaves may be of silver, bronze, emerald green, or steel blue over brown or they may be decoratively veined in contrasting brown, green, silver, or rose. Flowers are produced in a variety of shades from pink and red to lavender from early spring to late fall.

Listed in Table 1, are some widely grown and readily available gesneriads and suggestions for their use.

Gesneria and miniature sinningias (miniature gloxinias) are ideal subjects for dish gardens, terrariums, and dwarf flowering pot plants. Gesnerias are low growing (less than six inches), evergreen plants decorated year round with brightly colored tubular flowers borne on tiny peduncles. Miniature sinningias rarely exceed three inches in height but produce abundant large flowers (two inches in length) continuously throughout the year.

Saintpaulia ionantha (African violets), Sinningia speciosa (Florist's gloxinia) and stemless Streptocarpus rexii hybrids are the best known gesneriads in the trade, each being in cultivation for more than 50 years. As a result of hybridization within each group, a wide variety of flower colors can be obtained. Single, double, and multi-flowered varieties of African violet and gloxinia are available. African violets with ruffled and variegated foliage are common and all are everblooming. Streptocarpus hybrids are also everblooming while gloxinias tend to be more seasonal, flowering after three months of rest.

Pendant varieties of Streptocarpus are excellent hanging basket subjects producing funnel-form lavender flowers on wiry pedicels throughout the year.

DORMANCY IN GESNERIADS

Most temperate flowering plants respond to adverse environmental conditions, i.e. cold, by losing leaves and becoming dormant. Certain tropical species face equally adverse conditions, mainly those imposed by drought and also respond by entering dormancy. In the gesneriad family, sinningias and Achimenes naturally go dormant despite continued favorable growing conditions under cultivation. Seeing a prize gloxinia or magnificent Achimenes decline and die after months of lush growth and flowering is often more than a novice grower can bear, and the ``prize'' plant is subsequently discarded in a fit of anguish.

Do not despair, however, as these plants are perennials (flower over many years) and reemergefrom dormancy with vigor following a rest period. After the flowering season, foliage declines and gradually yellows or ``dies back.'' The surviving underground storage organs, tubers in gloxinias or catkin-like rhizomes in Achimenes, should be kept dry. For the next two to three months, water the barren pot monthly to prevent tubers or rhizomes from dehydrating. This is the best time to repot or to separate Achimenes rhizomes or slice gloxinia tubers for propagation. Small, pubescent ``rabbit ears'' just breaking the soil surface signal an end to the rest period and resumption of active growth. At this time, begin to gradually increase watering frequency and fertilization to normal levels.

PROPAGATION

Most gesneriads are commonly propagated from stem cuttings and seed. Sprinkle seed over moist soil in a pot and cover with glass or a plastic bag to prevent drying. Transplant seedlings to individual pots when one to two inches tall. Seedlings flower within five to seven months depending on species. Stem tip or mid-section cuttings of most species are easily rooted in a pot of moist soil or vermiculite/perlite mixture. Water frequently to maintain soil moisture and high humidity around the cuttings. Keep the rooting medium moist, but not soggy.

African violets, gloxinias, episcias, and Streptocarpus are propagated easily by leaf cuttings. Detach mature, healthy, green leaves with part of petiole, if present, from the parent plant and cut notches across major veins on the undersides of the leaves. Place the leaves on the soil mix, undersides touching the mix, bury the cut end of the petiole, and weight the leaves down to prevent curling. Plantlets will develop from the cut surfaces within several months. African violet growers prefer to stand the leaves vertically or slightly sloped to a 45° angle with one inch of petiole planted in the propagation medium. Plantlets then develop below the soil line from the petiole.

African violets and Streptocarpus tend to form clumps when propagated from leaf or petiole tissue. Specialists prefer to grow single stemmed plants and use offsets as propagating or trading stock. Break the offset shoot from the parent plant and then pot it in the standard potting mixes.

Achimenes may be propagated during its dormant season by digging and separating rhizomes or by breaking individual rhizomes into one half inch pieces prior to repotting. When repotting, bury rhizomes about one inch deep.

MEDIA AND CONTAINERS

A medium for gesneriads should be light, well drained, and porous yet have a high water holding capacity. Commercial growers and researchers agree that ``soilless'' mixes composed of peat and sand, vermiculite, or perlite are best suited for growing gesneriads. A popular mix consists of 50% peat and 50% perlite or vermiculite amended with two tablespoons of dolomitic limestone for each quart of prepared mix. Better still, artificial mixes suitable for gesneriads are available in many retail nursery stores. Since best growth is obtained when the mix is light and porous, avoid pressing the medium around the roots but gently tap the pot to settle the mix.

All types of plant containers may be used for gesneriads, with just one stipulation: drainage must be provided. Plastic, clay, and glazed pots are commonly used for pot plants. Plastic, wire, and redwood containers find use as hanging baskets. Dish garden and terrarium enthusiasts use all kinds of containers from thimbles for Sinningia pusilla (smallest of the miniatures) to teacups, brandy glasses, and aquariums for larger specimens.

WATERING AND FERTILIZATION PRACTICES

Keep actively growing gesneriads moist at all times. Lack of moisture wilts flowers, reduces their lasting quality, and in Achimenes and Sinningia leads to premature dormancy of plants. When watering, saturate each pot thoroughly so that moisture drains from the bottom of the pot. Overhead watering is satisfactory for all gesneriads and does not contribute to leaf spotting unless the water temperature is 10°F (5.5°C) or more degrees warmer or colder than the leaf temperature. A good rule to follow to avoid cold water damage is to keep a container of water in the room or greenhouse where plants are grown so that water and plants are the same temperature. African violet growers use self-watering techniques, where water is drawn into the soil through a mat, by capillary action from a reservoir below the pot.

A complete fertilizer with a 111 ratio is recommended for gesneriads. These fertilizers are available in soluble, dry, or slow release formulations. Fertilizers with the same basic ratio may be interchanged but be sure to adjust for changes in concentration. For instance, a recommendation may be given in terms of 202020, i.e. one half tablespoon/gallon, but a 101010 fertilizer may be all that is available. Use the 101010 but keep in mind that this material is half as concentrated as 202020; therefore, compensate by using one tablespoon/gallon.

Slow release type fertilizers such as Osmocote, ProGro, MagAmp, etc. release nutrients slowly over a period of two through months. One application of Osmocote 141414 at the rate of one and one half teaspoon per six inch pot is sufficient for two to three months, and plants will be continuously fertilized. Soluble fertilizers are dissolved in water and applied in place of a normal watering. Mix one half tablespoon/gallon of 202020 and apply monthly. Dry materials such as 202020 garden fertilizer can also be used for gesneriads at rates of one half teaspoon per six inch pot applied monthly.

Over fertilization, "salty" irrigation water, and poor watering practices contribute to high soluble salt levels in the soil, which cause root damage and subsequent yellowing of leaves. A good habit is to leach thoroughly each time plants are watered to prevent fertilizer and salt build-up in the growing medium.

LIGHT AND TEMPERATURE

Gesneriads require partial shade for optimum growth and flowering. Achimenes, Aeschynanthus, Codonanthe, Columnea, Nematanthus, and Sinningia thrive at light levels between 2,000-2,500 fc (20-25K lux). Episcia, Saintpaulia, and Streptocarpus grow best at 1,000 fc (10K lux). These shade levels may be obtained by growing plants under saran cloth or trees, shading the greenhouse with whitewash, or by utilizing shady corners in and around the house. Gesneria, miniature sinningias, episcias, African violets, and Streptocarpus grown indoors will flower with as little as 750 fc (7.5K lux). Position pots, dish gardens, and terrariums near southeast, south, or southwest facing windows and filter direct sunlight through sheer curtains if possible.

Tropical gesneriads need to be protected from cold temperatures. All species discussed earlier will stop growing when temperatures are between 50-55°F (10-13°C). Gesneriads are tropical plants and will be damaged when subjected to temperatures of 50°F (10°C) or below for a period of six hours. Plants will continue to grow and flower if night temperatures are maintained within a range of 65-75°F (18-24°C).

INSECTS AND DISEASES

Florida gardeners need to be aware that gesneriads are susceptible to a number of diseases and insect pests. Generally, problems of this nature may be minimized by practicing the cultural and sanitary techniques described below.

1. Use pre-sterilized soil components or artificial mixes sold by garden centers. Bagged peat, vermiculite, and perlite are usually sterile, but sand may not be.

2. Space plants to increase air circulation, reducing the potential for disease.

3. Water early in the day so leaves and crown are dry by late afternoon; better still, avoid wetting foliage when watering.

4. Remove weeds as these may harbor insects and diseases.

5. Remove yellow, dead, and decaying plant parts.

6. Allow water to drain from pots each time plants are watered.

Despite conscientious efforts to prevent pest problems, occasionally they arise and some pesticide treatment may be necessary. Consult your local county agricultural Extension agent for the latest pesticide recommendations.

Common insect pests that Florida's gesneriad growers may face are the following.

• Mealybugs--small, white, cotton-like animals infesting axils and undersides of leaves. These insects are very bothersome but are easily controlled on a few plants by squashing individuals with cotton swabs. Root mealybugs reside in the soil and feed on roots, causing the plant to slowly deteriorate. If root mealybug is suspected, knock plants from pots and look for cottony masses in the medium.

• Mites, particularly microscopic Cyclamen mites. These insect pests infest and feed in tiny bud leaves and flowers, distorting their shape or if severe causing abscission. During warm and dry weather, mite populations flourish. Therefore, keep watch for mite damage and treat with miticides if necessary. Misting plants frequently during hot weather helps reduce mite infestations.

• Aphids and caterpillars. These insect pests are sometimes encountered. Aphids, or plant lice, are soft-bodied yellow, green, pink, or black insects which damage new growth by sucking plant juices. Caterpillars devour chunks of leaf tissue, rendering the plant unsightly.

Gesneriads are subject to several diseases, but their occurrence can be minimized if the guidelines presented earlier are followed. However, be on the lookout for:

• Root and crown root--roots, stems, and leaves become limp, soggy, dark brown, and water soaked. Nothing can be done to save plants once infested, so discard it immediately and propagate from healthy stock. Be sure to use sterile propagating and potting mixes.

• Bud rot (Botrytis)--humid crowded conditions and wet leaves are conducive to development of a gray mold infecting leaves, buds, and flowers. To reduce the occurrence of Botrytis, space plants to provide adequate air circulation and remove dead flowers promptly. Avoid wetting flowers and foliage when watering.

WAYS TO PROPAGATE A FLORIST OR HOLIDAY GLOXINIA

After bloom, remove all spent flowerstalks and grow the plant for one to two months. Gradually reduce water until foliage turns yellow and dies. Remove withered and dead foliage, withhold water, and store in a dry area. After two to four months the bulb will generate new shoots. When shoots become visible (commonly called rabbit ears), dig bulb and cut into two or more pieces and plant the pieces into individual pots. Apply small amount of fertilizer and water. If only one multiple crown plant is desired, leave bulb in original pot, apply fertilizer, and water.

A large number of plants can be obtained from seeds of one plant. After flowers are spent, remove flowers but allow flower stalks to remain. Flower stalks that do not contain viable seed usually wither and these should be removed. When seed pods begin to open, remove entire seed stalks and collect seed by gently tapping stalks over a piece of white paper or sprinkle seed directly on a commercial germination medium. Without covering the seed, soak the container in water until the medium is moist. Cover container with a piece of glass or plastic and place near a window receiving indirect sunlight. When seedlings are large enough to handle, transplant them into individual containers.

Cut leaves from plant after bloom and place them on a growing medium such as sterilized sand. Cover parts of the leaves with growing medium to hold the leaf margins in close contact with the medium. Cut or injure leaf margins with a clean sharp knife to initiate the formation of small plants along the margins of leaves. Keep medium moist and cover container with clear glass or plastic. To prevent rotting of leaves and establishment of disease organisms, do not allow the glass or plastic to touch leaves where there will be water condensate. This prevents condensate from dripping on leaves. When a clump of small plants have developed sufficiently to handle, remove them from the leaf. Multiple plants can be planted when a multiple crown plant is desired or separated to obtain single crown specimens.

Cut leaves from plant leaving one and one half inch of each leaf stem (petiole). Place the petiole into a moist sand medium about one half to one inch deep. Roots will appear at the base of the petiole in three to four weeks under good growing conditions. In six to eight weeks, leaves of new little plants will appear at the surface of medium. Separate and pot each plant individually, in single-crown plants are desired; do not separate for multiple crown plants. Discard the original leaf cutting.

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer, Interim Dean.

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