Cultivation Of African Violets

The important factors to consider, when growing African violets, are light, temperature, compost,
pots, correct watering, humidity and feeding.

Light

All plants require a good intensity of light to grow and produce flowers.
The action of light upon the chlorophyll in green-leaved plants converts,
by the chemical process of photosynthesis, water, carbon dioxide and
fertilizers into sugar foodstuffs that the plants can use for growth.
Different plant genera require different light intensities, and therefore one
must consider the conditions of their original habitat to be able to provide
them with light of somewhat similar intensity.

Although African violets originated in East Africa close to the equator
and therefore in the tropics, their natural habitat was in rocky areas near
water shaded by trees and not in open, intensely sunny situations.
Another point to remember is that at the equator, day and night are of
equal length and so African violets require periods of light and dark during twenty-four hours.

Knowing all this, we can safely say that during the summer months they
require the intensity of bright diffused light, but not direct hot sunshine; in
fact when exposed to the latter the foliage of the plant becomes exceedingly
pale, stunted in growth, shriveled and burned, so that the plant ultimately
dies. One way to assess the light intensity falling on a plant in summer is to
hold one’s hand between the plant and the sunlight and then to look at its
shadow on the plant. If the shadow is clearly defined, the sunlight is too
strong and the intensity too high, in which case the plant should be moved
to another, shadier position. If the shadow of the hand can just be seen, the light intensity is just right.

During the winter months, the light intensity of the sun is greatly
reduced so that in northern latitudes African violets may be fully exposed
to it and not be harmed in any way. In fact in these latitudes the light
intensity is not sufficiently adequate nor of a long enough daily period to
promote budding, and so African violets are said to rest. It is possible to
increase daylight length in winter with the use of fluorescent light tubes.

Position in the home
Any reduction in light intensity is not appreciated by the human eye as
much as it is by plants; thus what appears to us as a bright position in a
room may well seem to be very dark to a plant. From this it can be
understood that although a table in the centre of a room is a good position
for us to enjoy a flowering African violet, it is not the place for it to stay
for more than a week without it losing some of its beauty; any leaves and
flowers will pale, and budding will cease. Remember that light intensity
falling on a plant at a window is reduced by about 50 per cent when that
plant is moved about 2ft (60cm) in from that window.
Therefore when growing African violet plants on a window-sill, they
should be placed as close to the glass as possible during the daytime. Early
morning and early evening direct sunlight are not detrimental to African
violets, and so plants may be kept safely on east- or west-facing
windowsills all the year round. However south-facing windows, or any that get
full summer sunshine, should be avoided if at all possible unless shaded by
a tree outside to give filtered light. Otherwise either a thick net curtain
should hang between the glass and the plant, or the plant should be
brought further into the room during the hottest period of the day and
then returned to the window-sill in the late afternoon. In winter,
however, south-facing window-sills generally prove to be a good position for
African violets, as any sunlight there is at that time of year will be
beneficial. Windows of northern aspect provide a good position in the hot
summer months, but not during winter, as these window-sills are then
much colder and do not have a long enough daylight period to sustain the plants.
Whenever plants are grown on window-sills they should be turned by
a quarter turn each day in order that they grow evenly, straight upright. If
this is not done, the leaves on the side of the plant furthest away from the
window will grow reaching for the light, and the whole plant will end up
growing at an angle, leaning towards the window.
Growing under fluorescent lighting
It may not be realized that given adequate conditions of light, African
violets are capable of flowering all the year round. These conditions may
be achieved by using artificial light, of which the best source is a
fluorescent tube with a light emission equating closely to the intensity of
natural sunlight. The spectrum of the latter contains all wavelengths from
far red through orange to green to far blue, all of which are either
reflected or absorbed by plants. We see plant foliage as green because the
yellow and green wavelengths are reflected back by the leaves as little
used, whereas red and blue wavelengths are absorbed by the leaves and
used in photosynthesis and other growth reactions.
Fluorescent tubes are normally termed ‘warm white’ and ‘daylight’ or
‘cool white’. Experience has shown that a fluorescent tube fitment
holding one warm white tube and one daylight tube, alongside each
other but 6 to 9in (15 to 23cm) apart, give the intensity and type of light
that produce good growth in African violets. There are also fluorescent
tubes made for horticultural use which appear pink or blue in color to
us when lit. These can give an increase in growth level, although for the
amateur this particular increase does not really merit the extra cost,
which is at least twice as much as the cost of warm white tubes. Today
there are also low-energy tubes available which can be fitted into a light
system; these give good light intensity and useful wavelengths using less electricity.
By comparison with fluorescent light, incandescent light -such as that
from household light bulbs -produces a great deal more heat, it is not as
useful a light spectrum, and such bulbs are much more expensive to run.
However, in the winter months a plant that normally lives on a
windowsill will benefit from a few extra hours of light when placed under a
lighted table lamp during the evening.
The best way of using fluorescent lighting for African violets is to have
it fitted either in individually shelved plant stands, or under shelves built
into a dark corner in a room. Open-fronted bookcases may also be
utilized, providing their shelves are of an adequate size to hold plants
without crushing the leaves, and are far enough apart for the foliage and
flowers not to be damaged by being too close to the tubes.
Shelves housing standard-sized plants should be about 2ft (60cm) apart
so that the fluorescent tubes are approximately 18in (45cm) above the
plant foliage. When growing miniature hybrids, the distance between
tubes and foliage should be reduced to about 6in (15cm). This can be
achieved by raising the miniature plants, placing them on upturned pots
or something similar of a suitable height, and is relevant if a mixture of
African violet plants of different sizes are being grown together on the same shelf.
The best distance to maintain between fluorescent tubes and each type
of plant must be found by experiment. The plants themselves will tell you
whether or not they are happy with the distance between them and the
tubes: their leaves will turn down to hug the pot if they are too close to
the light, or they will reach up towards the light when it is too far away.
For optimum growth, fluorescent lighting should be switched on for a
period of twelve to fourteen hours a day, or for a maximum of sixteen
hours, because African violets grown under artificial light must have a
minimum of eight hours of complete darkness. Again, only by
experiment can you find the exact number of hours of light to give, in order to
achieve the best growth results.
It should also be noted that light intensity differs along the length of a
fluorescent tube. With this in mind, African violets with light-colored
flowers and leaves should be positioned towards the tube ends as they
require a lower light intensity than dark-colored flowers and leaves;
these latter should be placed towards the centre of the tube length.
Variegated foliage plants should also be positioned centrally, as their
optimum growth is encouraged there whether they are light or dark colored.
Plants grown under fluorescent lighting should stand on watertight
trays fitted with capillary matting for ease of movement; gravel would be
too heavy. The matting should be kept moist to create humidity.

Temperature

Although equatorial, African violets do not require tropical temperatures
since all the species have their habitats at altitudes up to 4,000ft (1,200m)
and so are actually growing in cooler temperatures.

The best temperature range for good growth is
65-75°F (18-24°C) during the daytime, with a night-time drop of 10°F
(5°C). During the summer months, high temperatures can be a great
problem and a period of four or five days at a temperature of 85°F (29°C)
and over will almost certainly prove fatal to African violets. It may be
helpful to increase the levels of humidity and ventilation. Then during the
winter months the problem shifts to too cold a temperature: whilst an
African violet will just survive a short period at 55°F (13°C) by ceasing to
grow, once the temperature falls below 50°F (10°C) the plant will collapse and die. It is advisable during such cold spells to reduce watering in
order to prevent damage to the roots as much as possible.

In summer, open windows will provide air circulation that will normally
control room temperature somewhat; it is only when excessively hot
weather lasts for a week or more that African violets suffer heat exhaustion
and collapse. In this situation there is very little that can be done, other than
to keep the air moving by using an electric fan or air conditioning
equipment. Centrally heated homes in winter give the warmth needed to keep
plants in good order, provided that the heating is not tuned off overnight.
However, it must be emphasized that plants should not be left on
windowsills behind drawn curtains, because even if the windows are double glazed,
it will still be much too cold for them overnight.

Compost

Most of the African violet species were found growing among rocks in
very little soil, and this was composed mainly of humus. From this is can
be understood why the root system is shallow, with hair-like roots, and
why it requires an easily draining compost.

Over the years many types of compost have been used, and it is for the
grower to find the compost which is most suitable for growing African
violets in the conditions provided. One very important fact to remember
is that whatever the growing mixture, ideally its pH value should be between 6.7 and 7.0.

Excessive acidity or alkalinity has a detrimental effect on the beneficial
micro-organisms, or bacteria, by reducing their populations in the
compost so that they cannot convert the essential nutritional elements into a
form that the plant roots can absorb for growth. To avoid much of this
problem, standard and large-sized show African violets should be root
pruned and repotted every six months, and miniature and semi-miniature
plants every three to four months.

Correcting pH value in a compost
Fresh potting compost should always be of the correct pH value, and if it
is not, then correction should be made. A compost which is too acidic,
below pH 6.6, may be improved by adding to the potting mixture
dolomitic lime containing magnesium carbonate, rather than
calcium
carbonate -although dolomitic lime does contain some of the latter
compound. Ordinary garden lime contains very high amounts of calcium
compounds, and so should not be used as it will completely burn the root
system, thus killing the plant. Too alkaline a compost can be corrected by
watering the plant with a solution consisting of one teaspoon (5ml) of
distilled white vinegar to one gallon (4.5 liters) of water. This process is
obviously a slow method of correction as it is carried out on a potted
plant. Also for correcting alkalinity there are pelleted, slow-release
sulphur chips; these can be crushed so as to incorporate them
evenly into a batch of compost before it is used.
Whichever way the correction is made, whether from too acid or too
alkaline, the pH value should always be checked frequently using a meter
during the correction.
The constituents of compost
There are many commercial compost mixes, usually based on peat or peat
substitutes, and these have proved successful in use for many growers. However,
some people prefer not to use ready-mixed commercial composts but to make up
their own mix.
Peat – The best type to use is sphagnum moss peat; it is long stranded so
makes an open medium when used alone. Over a period of time it will
break down and become too acidic for good plant growth, therefore
repotting into fresh peat will be required fairly frequently. Garden or
sedge peat is much filler in composition, coming from a grass as it does,
and it readily compacts in use. It is also much more acidic, and correction
of the pH value would be required before use. Peat has no food value, and
plants would need feeding from the time of potting.
Coir – This peat substitute is produced from
coconut fibre and has been
used with varying success for growing African violets. It usually has a
neutral pH value of 7.0, although at times it has been known to have a pH
of 5.3, and so it should always be checked before use. Like peat it contains
no nutrients and therefore plants would need to be fed from when they are
first potted. Coir is preferred to peat by environmentalists as it is produced
from a renewable source, coconuts being an important world crop.
Bark – There are several grades of bark that may be used as a growing
medium. For African violets the pulverized grade should be used, although
at times this may be a little powdery. It is often used with other constituents
in compost mixtures. Again, always check its pH value before use.
Loam – Loam-based composts can rarely be used on their own for
growing African violets because they tend to compact in use so that the plant’s
fine root system cannot penetrate their mass. Normally loam has an
alkaline pH of 7.5 and above which would deter good growth of African
violets. Any loam used in a mixture should be pasteurized before use.
Pasteurization – It is always advisable to pasteurize any peat, peat substitute
medium or loam before use to kill any harmful organisms, insect
pests and
weed seeds that may be present. This can be done by heating the moist
medium in a closed pan in an oven at 180-195°F (85-90°C) for thirty to
forty-five minutes. It should then be stored in a closed container for two
days before use so that any beneficial bacteria that may have been set back
in numbers can re-establish themselves.
Pasteurizing is not sterilizing, which is steam heating in excess of 212°F
(100°C) for a similar period and would eradicate all the beneficial bacteria
present. Ready-mixed commercial composts should also be pasteurized,
especially if your local garden centers keep their stock uncovered in the
open. The unwanted organisms that can penetrate the packaging of
composts can be surprising.
Horticultural Vermiculite – This sterile medium is a mica mineral that has
been exfoliated, or expanded, by being heated to a very high temperature.
It contains no food value. The spongy pieces are made up of individual
plates of mica which hold water between them. It is most useful as a
course grade material to open up composts, and very much less useful as a
fine grade because of its propensity to break down into individual plates
which have no water retention properties. Always use horticultural grades
of vermiculite, as other grades are used for insulation and these are not
cleaned and so will contain substances harmful to plants.
Perlite – This is a white lava rock which has been expanded by treatment
involving great heat. It has excellent water retention properties, and is also
used to open up a compost mix. It is advisable to wet perlite before using
it, because the dust caused from minute fragments breaking away from
the larger particles can be an irritant to some people, especially those
suffering chest problems. Perlite is also a sterile medium and without any food value.
Horticultural Sharp Sand – The most useful type is river-washed sand. It
does not retain water, and is used solely as a compost opener to increase
drainage; there are various grain sizes, and a coarse grade will give good
drainage. Sand from the beach should never be used, as no matter how
much it is washed it will always contain salt and other harmful substances.
Other ConstituentsCharcoal may also be included in small amounts in a
home-made compost mixture. It is known as ‘a sweetener‘ because it is
able to absorb certain unwanted vapors from the mixture. Wood
charcoal pieces about 0.25in (0.75cm) square are a good size to include.
A balanced fertilizer also needs to be incorporated in any made-up
compost mixture that has no food value -although by far the best for
African violets is to use a soluble fertilizer when watering; then there is no risk of root burn.
Compost mixtures
Good general mixture for African violets is one part sphagnum moss peat
or peat substitute, to one part vermiculite or perlite; use a 4in (10cm) pot,
for example, as a measure. This mixture has no nutrients in it and
therefore soluble fertilizers should be given to the plants from when they are first potted.
Another recipe uses one part by volume each of peat and sharp sand,
the latter providing extra weight for pot stability especially when using
plastic pots. This mixture also requires soluble fertilizers to be fed, right
from the start of potting.
Loam-based compost may also be used as a constituent in a potting
mixture of one part loam-based, two parts sphagnum moss peat, and one
part vermiculite or perlite. This recipe has the advantage that feeding is
not needed until about four weeks after potting because of the nutrients
in the loam. The alkalinity of the latter is lessened by the acidity of the
peat, but the pH value should be checked on mixing.
Plants grown on a wick-watering system may need a
compost containing a higher proportion of perlite in order that it does not
become over-wet, even though perlite retains water. An example of such
a mixture is one part sphagnum moss peat, one part vermiculite and two
parts perlite, all by volume. Before using any home-made compost
mixture always check that its pH value is between 6.7 and 7.0, and correct if necessary.
It is by experimenting with various recipes that the best compost
mixture for one’s own growing conditions can be found. When
experimenting, for whatever reason, work with only two or three plants at a
time; never change an entire routine for the whole collection until good results are known.

Pots

As regards the kind of pot to use, clay or plastic pots are equally as good as
each other. Once again it is left to the preference of the grower, although
plastic pots are certainly easier to obtain these days. As to size of pot,
African violets prefer to be slightly pot-bound at all stages of their growth
and so the pot size is important. Plants should never be over-potted
because excess compost causes the leaf and flower growth to slow down
whilst the roots grow to fill the pot. Therefore always use the smallest pot
possible for the size of the plant.

For mature plants, a good guide to pot size is that the pot diameter
should be one third of the diameter across the foliage of a single-crowned
plant. Because African violets are not deep rooted, it is better to grow them
in dwarf or half pots. It is more difficult to decide on pot diameter when
growing trailing hybrids, as nowadays wide, shallow pans are often used so
that the branching stems may be pinned down for a better display. In this
instance it is for the grower to decide on the size of pan for the plant so that
it does not appear to be either over- or under-potted. If pinning down of
the stems is not wanted, always consider the type size of the trailer and
choose a size of dwarf or half pot that complements the plant.

Hanging baskets are currently very popular and may be used for the
growing of trailing African violets, that are not intended for show, by
planting several into and around a basket. However, hanging baskets tend
to be too large for their ideal display, so a single plant in a hanging pot is a
much better idea. These pots are available in sizes from 6in (15cm) in
diameter as against 10in (25cm) diameter baskets. Also available are plastic
hangers that may be attached to ordinary plastic pots of any size from 3in
(7.5cm) diameter upwards, enabling small-sized plants to be displayed to advantage.

It is good practice to root-prune and repot African violets at least once every twelve months; the best
time of year is in the spring as the outdoor temperature begins to rise and light levels increase.

Watering

There is no mystery about how to water, the mystery is in when to water,
and there is no hard and fast rule as to exactly when a plant will need to be
watered.  As a rule of
thumb, most of the root ball should be just moist at all times to allow the
very fine root hairs to carry out their function of taking in water, air and
nutrients. If the compost is either waterlogged or dried out, the root
system cannot carry out its proper function so the plant will wilt and die.
Thus to decide when a plant should be watered, use the finger tips to feel
whether the compost is moist about half an inch (1cm) below its surface.
If it feels dry there, water the plant; if in doubt, do not water but wait
until the following day and test again. Moistness is difficult to describe:
our definition is very damp, but not wet.

There are several ways of watering a plant: onto the compost from the
top; into the compost from the bottom of the pot; by standing the pot on
capillary matting; by a wettable wick from a reservoir.

Top watering
The water is poured onto the compost without wetting the leaves.
Enough water should be given for it to moisten the compost completely
and then drain from the bottom of the pot; the surplus must be discarded.
This is a preferred watering method for African violets being grown on
window-sills. Any water falling on leaves and left there when the plant is
in bright light or in a draught can damage them, and cause unsightly
brown patches to develop. If water does fall onto the leaves it must be
removed using a soft tissue.
Bottom watering
Water is poured into the saucer or dish in which the plant is standing.
More water should be added to the saucer if the plant soaks up all of the
first amount in less than ten minutes. Any water remaining in the saucer
or dish after twenty minutes should be discarded and the pot left to drain.
This method is also suitable for window-sill growing of African violets.
However, it is advisable periodically to water copiously from the top
because excess harmful salts will have collected on the surface of the
compost and this will flush them out. Care must be taken following this
water flushing that thorough draining is allowed.
Capillary matting
Plants standing on capillary matting will take up any water poured onto
the matting provided there is good contact between the holes in the
bottom of the pot and the matting surface. Care should be taken that the
matting does not remain flooded for longer than forty-five minutes at a
stretch. This method of watering has the added advantage of providing
extra humidity for the plants, and is useful when several African violet
plants are placed together on a window-sill tray.
Wettable wick
Wick watering from a reservoir is very useful when African violets are left
unattended for any lengthy period of time. A lidded container, such as a
tub that you would normally throwaway, is easily made into a reservoir.
A hole should be cut in the centre of the lid for the wick to pass from the
bottom of the pot into the water in the reservoir. A narrow wick, no
more than half an inch (1cm) wide, cut from an old pair of nylon
stockings or tights is best, and should be long enough to stretch from inside the
pot to lie along the bottom of the reservoir. String, cotton or wool should
not be used as these materials will rot if kept constantly wet, causing
problems for the plants. The wick should be thoroughly wetted before
one end is inserted into the compost at the bottom of the pot; capillary
action will begin immediately the other end is placed in the water in the
reservoir.

Humidity

There is another important factor associated with watering, and that is to
maintain a state of humidity around the plants. Invisible water vapor
produces a relative humidity, and this creates a beneficial micro-climate
for African violets whereby transpiration of moisture from their leaves is
lessened and the appearance of flowers and foliage is greatly enhanced. A
relative humidity between 50 and 70 per cent would be advantageous,
whereas below 40 per cent is too low -this will cause flowers to be sparse
and small, whilst buds will go brown and drop; also the leaves will lack
their normal lustre, their tips becoming brown in the low humidity.

In living room conditions, low relative humidity is the normal and it must
be rectified for plants to thrive. This may be done by grouping plants,
standing them over water or on capillary matting, and by misting.

Grouping Plants – Placing several plants together is a simple way of
slightly increasing relative humidity. Each plant will help its neighbors
by producing a micro-climate, and thus even less water vapor
will be lost by each plant so the stomata on the leaves will close. In hot
weather, however, and when central heating is needed, grouping plants
does not produce a large enough increase in the humidity. A slightly
higher level can be created by standing the grouped plants in bowls
of moist peat; although it must be remembered to lift the plants out of
the peat periodically so that their roots are prevented from growing into it.

Standing over Water – Another method used to increase humidity is to
stand the plants on constantly wet gravel held in trays. Care must
be taken that the plant pots are not standing in the water: the rule is
above the water, not in it. The water in the tray should be changed
frequently, and the tray and gravel washed so that they do not become
encrusted with lime scale and any small particles of compost falling from the pots.

Capillary Matting – Window-sill trays holding plants may also be lined
with capillary matting; this should be kept constantly moist but not wet to
produce extra humidity for the plants. Again, the matting should be
washed frequently to remove the excess salts left after the evaporation of
water from the matting. Good contact between the pot base and matting
usually means that some fine particles of compost soak into the matting,
and these should also be washed out.

Misting – In very hot conditions, plants may be misted twice a day using a
sprayer: this should contain hand-hot but not boiling water, and it should
be held about 2ft (60cm) away from and above the plants so that a fog falls
on them. The sprayer action which causes the formation of miniscule
droplets drastically cools the temperature of the water; this means that if
the water used in the sprayer is cooler than hand hot the mist or fog falling
onto the plants would be icy cold. In this event the plants would be
severely chilled and brown patches on the leaves would result. Any excess
moisture settled on the leaves or in the centre crown must be removed
using a soft tissue, and the plants allowed to dry out of draughts or direct sunlight.
The difference between misting and spraying should be appreciated.
The difference is in the size of the droplets falling onto the plants. In
spraying the droplets are much larger than in misting due to the sprayer being held nearer to the plants.

Feeding

Sometimes the importance of feeding an indoor plant is overlooked by
many people, who seem to think that a plant will grow without any
help from them; they are then disappointed when it withers away and
dies. It is important to understand what each nutritional element of a
fertilizer will do, the major elements being nitrogen (N),
phosphorus (P) and
potassium (K).

Nitrogen
This element has an essential effect on foliage growth because it helps to
build the green chlorophyll; thus it is greatly involved in the production
of sugars for use by the plant. Shortage of nitrogen results in leaves
turning yellow, and so a plant ceases to thrive. Too much nitrogen makes
for an abundance of leaf growth to the detriment of flower production.
Phosphorus
This element is almost as important as nitrogen in that it is involved in
converting plant starch into sugar; thus it promotes good flowering and
strong stems and roots. To show how effective it is in promoting flowering,
a mature plant that is reluctant to flower may be boosted into bud initiation
by giving it a small amount of super phosphate. Enough to cover a one
penny piece thinly is sprinkled over the compost surface and watered in.
This dose is repeated two weeks later, and it is usual that within six weeks
of the initial dose of super phosphate buds will be just showing.
Potassium
The main effect of potassium is on the root system, helping it to absorb other
nutrients and promoting vigor in the plant. It is also said to make plants
more resistant to disease and to cause them to withstand cooler temperatures.
Trace elements
Other elements in very small amounts also need to be present in a
fertilizer, and they are listed on the label as trace elements. These include
iron,
magnesium, manganese,
boron, copper,
zinc and vitamins, and all these
help to make a plant sturdy and healthy. It is normal for all commercial
fertilizers sold for houseplants to include all the trace elements. When pH
values in the compost are above 7.0, many of these trace elements are
locked in and cannot be absorbed by the root system -another pointer to
the importance of ensuring the correct pH value in growing plants.

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