|
 African
Violets
H. C. Jones
The African
violet (Saintpaulia) is an excellent flowering house
plant which will grow and flower under low light intensities
found in the average home. Where there is insufficient natural
light, they can be grown and flowered successfully entirely
under artificial light. Large numbers of different varieties,
types and colors available, and the ease with which they can be
propagated make this an excellent plant for interior decoration
of the home.
African
violets require about 1000 foot-candles of light for 8 to 12
hours per day for best growth and flowering. However, lower
light levels for longer periods of time are also satisfactory.
Often, it is possible to tell from their appearance whether
light levels are satisfactory. If light is too low, leaves are
usually deeper in color and thinner than leaves on plants
receiving higher levels of diffused light. Unless light is
extremely low, plants may grow well but will flower poorly or
not at all. In such instances, supplemental artificial light is
helpful in promoting flowering.
Excessive
light levels cause leaves to be pale or yellowish green, much
lighter than normal and some leaves may show dark areas where
they have been shaded by other leaves. Growth at high light
levels is slowed and plants become more compact, however,
although flowering may continue freely for a while it will
eventually decrease due to chlorophyll destruction.
The length
of time plants are exposed to light also affects growth and
flowering. Plants may receive proper light levels for only
several hours a day and thus insufficient total light while
plants in another location receive light of lower intensity but
for longer periods of the day, and thus more total light.
African violets should not be exposed to direct sunlight.
African
violets can be successfully grown when the only source of light
is from fluorescent lamps. Although incandescent lamps may be
used, fluorescent lamps give better results, are less expensive
to operate, and produce less heat. Plants grown entirely under
fluorescent light should receive approximately 600 foot-candles
of light for about 15 to 18 hours per day. This amount of light
can be provided by suspending two 40-watt fluorescent tubes 12
to 15 inches above plants. Tubes should be mounted in suitable
fixtures equipped with reflectors.
African
violets grow best at a night temperature of 65 to 70°F, but
will grow satisfactorily at 60 to 80° F. Temperatures in
Florida often exceed 80° and under prolonged high temperatures
growth and flowering are reduced. If possible, place plants in
the coolest place in the home during these periods or in an air
conditioned room.
African
violets tolerate dry air, but need higher humidity for best
growth and flowering. Humidity around plants can be increased by
setting pots in water-tight metal or plastic trays filled with
wet pebbles or sand. Care must be taken to avoid placing pots
directly in water to prevent root damage.
Drainage is
one of the most important considerations in preparing a soil
mixture for African violets. An excellent mixture of readily
available materials may be prepared by mixing equal parts (by
volume) of soil, sphagnum peat, and horticultural grade perlite.
Excellent plants can also be grown in mixtures consisting of
equal parts of sphagnum peat moss and perlite. Commercially
prepared packaged soil mixtures are also available for African
violets. Soil mixtures should have a pH of about 6.0 to 6.5 or
be slightly acid for best results.
Sterilize
soil and used pots before planting to kill disease organisms,
insects, nematodes and weed seeds that may be present. If the
suggested soil mixture is used, only the soil need be
sterilized, since new sphagnum peat and perlite are usually
sterile. Most commercially prepared soil mixtures are
sterilized. Soils may be sterilized by placing in a container
and heating in an oven. For best results soil should be slightly
moist before sterilization and heated to 180 degrees Fahrenheit
and held at that temperature for 30 minutes. Old clay pots may
be sterilized by the same procedure used for soil. Plastic pots
will not withstand heat sterilization, but can be re-used after
washing thoroughly with soap and water or a dilute chlorox
solution.
A definite
schedule for watering African violets is not desirable since
frequency and amount of water required varies with soil mixture,
drainage, light, temperature and humidity under which plants are
grown. Type of pot used also has an important effect on
frequency of watering, as plants in clay pots require more
frequent watering than those in plastic pots since evaporation
is greater. Decorative glazed pots without drainage holes are
generally unsatisfactory due to lack of drainage. In general,
water should be applied whenever the surface soil feels dry to
the touch, but before it becomes hard or the plant wilts.
African
violets may be watered from the top or bottom. When watering
from the top, apply sufficient water to surface soil to
thoroughly saturate it and discard excess water which drains
through the bottom of the pot. Watering from the bottom may be
done by placing the pot in a container to which about 1'' water
is added. When the soil surface becomes moist, remove the pot
and pour out of excess water. "Wick'' watering may also be
used.
Temperature
of the water should be the same as that of the room or slightly
warmer to avoid any chance of spotting leaves if water contacts
foliage. Chlorinated or fluorinated water, if satisfactory for
human consumption, is satisfactory for African violets.
Many
completely water-soluble fertilizers containing nitrogen,
phosphorus, potassium and other required nutrients are sold for
use on house plants and African violets. The safest way to apply
dissolved fertilizer is to give the soil a normal watering from
the top, apply fertilizer from the top and then discard excess
water and fertilizer solution that drains from the bottom.
Plant
growth and color often indicate need for fertilizer. A gradual
loss in leaf color combined with a reduced growth rate usually
indicates that fertilizer is needed. If in doubt as to whether
plants need additional nutrients, fertilize one or two and wait
about 10 days to see how they react. If plant growth is evident
and they become darker in color, the rest of the plants may be
fertilized.
African
violets may be propagated easily by leaf cutting, and about 6 to
9 months are required to obtain flowering plants. Any leaf is
satisfactory if healthy and firm. Remove the entire leaf with
petiole (leaf stem) by snapping or cutting it off at the stem of
the plant and trim the petiole to about 1 to 1 1/2 inches in
length. A combination of half vermiculite and half sand, by
volume, makes an ideal propagating medium or the soil used for
growing plants may be used. Insert the petiole into the medium
by pushing it into a hole made with a pencil or similar tool.
Roots normally appear at the petiole base in 3 to 4 weeks under
good conditions and leaves of the new plants appear at the
medium surface 3 to 4 weeks after root formation.
Old
multiple-crown plants may often be successfully propagated by
division. Carefully cut each crown away from the plant so that
each plant has its portion of the root system. Each division is
then potted in the soil mixture.
Old plants
often develop a short stem which cause them to have a ``leggy''
appearance. Usually such plants may be successfully re-rooted by
cutting the plant off at the soil level and inserting the old
stem in the same medium used for rooting leaf cuttings.
New plants
brought into the home should be examined thoroughly for signs of
insects and diseases and kept separated from other plants. If
they appear healthy at the end of about 6 weeks it is usually
safe to set them with the other plants.
Control of
most insects and mites can be obtained with insecticidal soap
sprays. Mealy bugs may be controlled by mixing alcohol with an
equal amount of water and touching each insect with a cotton
swab dipped in the solution.
Cyclamen
mites which causes a severe stunting of plants is difficult to
control and where only a few plants are concerned, they should
be discarded. If many plants are affected, Kelthane sprays may
be used. Be sure to read and follow all label directions on
pesticides used on african violets.
Various
disease organisms may affect african violets from time to time,
but adequate spacing of plants, use of sterilized soil,
provision for good air circulation, prompt removal of faded
flowers and unhealthy leaves, and control of thrips and mites
are all important preventative measures.
Once a
flower or leaf disease is noticed, spraying with captan or
mancozeb will often aid in controlling the disease. Read and
follow all label directions when applying a fungicide to african
violets.
Root
diseases usually result from over watering of plants. Symptoms
may not show up on the leaves until severe root damage has
occurred. In most cases with root diseases or damage the best
control is to discard the plant and purchase new healthy ones.
Some
problems caused by cultural factors include ring or leafspot and
petiole rot. Yellowish rings, spots or streaks on the upper
surface of leaves are caused by cold water touching relatively
warm leaves. This can be avoided by using water at room
temperature or slightly warmer than leaf temperature. Petiole
rot occurs when petioles touch the edge of the pot and develop
brown, sunken areas at points of contact. The injury is
localized and does not cause the petiole to rot unless disease
organisms enter the wound. This trouble is the result of
chemical injury caused by the accumulation of soluble salts at
the pot rim of clay pots. This problem can be reduced by using
fertilizers sparingly and applying sufficient water to
thoroughly saturate the soil. When water is applied to the soil
surface, excess water and the salts will drain out the bottom of
the pot. Petiole rot can also be avoided by waxing the pot rim
or covering it with aluminum foil.
Copyright
Information
This document
is Fact Sheet ENH-17, a series of the Environmental Horticulture
Department, Florida Cooperative Extension Service, Institute of
Food and Agricultural Sciences, University of Florida. First
published: June 1990. Revised: February 1991.
This
document is copyrighted by the University of Florida, Institute
of Food and Agricultural Sciences (UF/IFAS) for the people of
the State of Florida. UF/IFAS retains all rights under all
conventions, but permits free reproduction by all agents and
offices of the Cooperative Extension Service and the people of
the State of Florida. Permission is granted to others to use
these materials in part or in full for educational purposes,
provided that full credit is given to the UF/IFAS, citing the
publication, its source, and date of publication.
http://edis.ifas.ufl.edu/BODY_MG028
|
