Orchids
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These very beautiful plants have
tended to suffer from a bad press. There seems to be a general impression that
they are very difficult to grow, requiring dedication, patience and special
growing conditions. Some do but many are easy-going plants that most gardeners
can succeed with.
Probably the most limiting factor
in your choice of orchids is the severity of frost your garden experiences and
the amount of winter rainfall. There are a few very hardy orchids but most of
the more commonly grown genera are somewhat frost tender though few require
sub-tropical conditions.
Winter rainfall is an important
consideration if you intend to grow the hardy terrestrial orchids such as Pleione
or Cymbidium outdoors. Too much rain combined with cold weather will
cause rotting.
The native orchids are seldom cultivated except by dedicated
enthusiasts. They are mainly hardy plants but seldom do well in cultivation.
Some species have very precise growing requirements.
Doubtless you will be able to
grow a wider range and achieve greater success if you can build some sort of
green house or other protective structure. This doesn’t need to be anything
very elaborate. A simple lean-to structure attached to a garage will be
perfectly adequate in most cases.
Orchid Cultivation
Growing Conditions
Orchids vary considerably in
their demands. Some need the conditions that only a heated greenhouse can
provide, others will grow outdoors under normal conditions, most fall somewhere
between the two extremes. Enthusiasts don’t baulk at the power bills that
growing warm temperature orchids bring but most of would find them too
expensive. However a wide range can be grown with minimal heating or even in an
unheated frost free greenhouse.
Cymbidium, Cattleya,
Odontoglossum, Paphiopedilum, Coleogyne and Lycaste are some of the
more tender genera that can be grown without having to use too much extra
heating. They get by perfectly well with winter minimums of 10°C and will
tolerate lower temperatures for short periods. Cymbidium and some Coleogyne
species can be grown outside year round in frost free areas.
In many ways the hardy outdoor
species are more difficult to grow. Not because they can’t tolerate the cold
but because of other seasonal factors, such as humidity levels and rainfall.
The most commonly grown is Bletilla striata but it is seldom a
spectacular plant. Pleione is a more interesting genus. Often grown in
alpine houses these hardy terrestrial orchids may be grown in gardens if
special attention is given to drainage and siting.
Orchids generally require bright
indirect light. Most will tolerate direct sunlight for a few hours a day but
not through glass. Many orchids will tolerate poor light for extended periods
but their flowering will be adversely affected.
Maintaining the humidity above
50% is important, below this orchids will suffer, 65%–90% is preferable. The
easiest way to achieve this in a greenhouse is to spray the floor and other
surfaces with water. The evaporating moisture will raise the humidity. In
winter lower humidity levels are preferable; the plants are not so active at
this time and lower humidity will lessen the prevalence of fungus diseases.
Good ventilation is also
important in preventing fungus diseases. Those inexperienced in greenhouse
growing tend to close all the vents in winter to keep in as much heat as
possible but good ventilation is just as important as maintaining the right
temperature. When temperatures rise in summer adequate ventilation is the best
means of avoiding overheating. As a rule a greenhouse should have a vent area
roughly equal to a third of the floor area.
Greenhouses
There are several styles of
greenhouses available to the home gardener. Which you choose will be dictated
by the conditions you wish to maintain and the price you can afford to pay.
In the long run the commercially
made metal framed glass is house is the cheapest to run but the initial outlay
is high. Plastic skinned tunnel houses are a cheaper alternative but they
require re-skinning every five years or so.
The cheapest alternative is an
entirely home built greenhouse and in many ways it’s also the most
satisfactory. Doing it yourself means that you get the size and design that you
want. The work involved shouldn’t tax even a mediocre carpenter.
The construction doesn’t need to
be anything elaborate. A simple wooden framework will be quite adequate. 100mm ×
50mm timber is heavy enough for the main structure with 50mm × 50mm for
intermediate support and bracing. Anything lighter than 50mm × 50mm is likely
to warp excessively. Use only ground treated timber, H4 grade or better.
Painting the woodwork white will
reflect more light but most greenhouses are bright enough. Painting or staining
will, however, extend the life of the timber.
Very few of us are competent
glaziers so plastic skinning is the preferred covering. Use proper
horticultural film of at least 140 microns but preferably the 200 micron grade.
Rigid fibreglass or polycarbonate sheeting is a longer lasting alternative but
is expensive for all but very small structures.
Secure the plastic with 50mm × 12mm
battening strips. Where the plastic meets the ground either secure it to a
partially buried wooden beam at ground level or leave some surplus that can be
buried. This should eliminate drafts at ground level, which can be very
damaging.
Unless you have a proper double
skinned or double glazed greenhouse you will need to add extra insulation in
winter. The bubble plastic used in packaging is effective but better still are
the horticultural grade infra-red reflecting plastics. These can be stapled to
a wood framed house or taped to a metal frame.
In most parts of the country some
form of winter heating will be necessary. Electricity is the easiest to use and
probably the most economical as electric heaters can be run off simple
thermostats for maximum efficiency. Kerosene, natural gas and coal boilers are
alternatives but they require careful setting and maintenance, are often
expensive to install, and may produce poisonous fumes.
Containers
The traditional terracotta pot
has long been favoured for orchids. These have the advantage of being porous,
which means there are no drainage problems and the roots are kept well aerated.
Unfortunately terracotta pots are expensive when compared to plastic and they are
easily broken, consequently plastic is now the more widely used material.
Most pots are suitable just as
they are but make sure they have adequate drainage holes. Extra holes are
easily made in plastic pots either with drills or a heated metal rod, such as
the tip of a soldering iron.
Hanging baskets made of wire or
interlaced wooden strips are alternatives to traditional pots. Unlike the
hanging baskets used for regular plants these are usually not lined. Instead a
very coarse soil mix that will not fall through the holes is used. If necessary
a thin lining of sphagnum moss will keep the mix in place.
Epiphytic orchids can be often be
grown in pots with very coarse potting mix but are better grown in the hanging
basket type container. This is because their roots can reach the air more
easily. Some epiphytic orchids resent being confined in containers, these are
best grown on slabs of tree fern or other bark. Until the roots gain hold the
plants will need to be firmly tied to the support with a strong but unobtrusive
thread.
Potting Mixes
Orchid mixes are very coarse and
open compared to the more familiar potting mixes. Those unfamiliar with this
type of soil wonder how it can possibly retain enough moisture for plant
growth.
The answer is in the nature of
the orchids grow habit. Most orchids have a conspicuous food storage organ
known as a pseudobulb. The plants can survive for considerable periods on the
reserves stored in the pseudobulb. The roots serve to recharge the pseudobulb
and operate best in well drained and aerated soils. Too much moisture or too
little air will rot the roots and ultimately the pseudobulb.
Orchid roots actually attach
themselves to the soil material and so bind the soil to the plant. Anyone that
has ever tried to clear the soil mix from Cymbidium will be familiar
with the way the roots grasp the larger chunks of bark or fern fibre.
Most modern orchid mixes are made
from composted bark. Regular bark based mixes can be used if they are sieved to
remove the very fine material. The fine sievings can be used as seed raising or
cutting mixes for other plants.
Even this mix may retain moisture
for too long so add some coarse bark or polystyrene bubbles. Experiment with
these materials until you have an extremely free draining open mix.
Watering and Nutrients
The mix should not remain
obviously wet for more than a day or so after watering. Prolonged or repeated
periods in wet soil will lead to rotted roots.
Watering is not so much a matter
of how often to water but how quickly the plant dries out between waterings.
Epiphytic orchids usually need to dry out within a day or two of watering or
they may rot. Terrestrial orchids tend to prefer soils that retain moisture
longer.
Your soil mix consistency will go
a long way to avoiding any rotting problems. Keep the mix open and coarse for
epiphytes and a little more dense and moisture retentive for terrestrials. Once
you have the right soil consistency when to water is generally quite apparent.
This all seems more than a little vague but it’s really a matter of experience.
Although orchid soil mixes may seem to be very lacking in
nutrients most of the common genera will thrive in them, however, like any
plants they will eventually need feeding. There are a number of pre-mixed
orchid fertilisers available and most are quite satisfactory provided the
directions are followed. Do not overfeed orchids; they are quite easily killed
by that sort of kindness.
Enthusiasts will blend their own
fertilisers but most home gardeners would be better to stick to a commercial
formula. If you do want to make up your own mix it pays to thoroughly research
the particular plant’s requirements.
Propagation
The easiest method of propagation is division of the
clusters of pseudobulbs. This eventually has to be done even if you don’t
require more plant as an orchid in an overcrowded pot will eventually cease to
flower.
Some orchids will produce stems
with aerial roots. These can be removed from the parent plant and grown on.
Orchids with rhizomes rather than obvious pseudobulbs can be divided or pieces
of rooted rhizome can be removed and grown on.
Growing from seed is another
method but requires care. Orchid seed is generally very fine and seldom
germinates well if sown on soil in the usual manner. The accepted method is to
sow the seed in sterile flasks on a nutrient enriched agar jelly.
The exact make-up of the nutrient
solution varies from genus to genus. If you wish to try this method contact
your local horticultural society or orchid society for details of some of the
more common formulas.
Tissue culture is widely used in
commercial orchid propagation. Cultured plants are available from specialist
growers.
Pests and Diseases
Orchids grown indoors are subject
to the same pests and diseases as most greenhouse plants. You will probably be
familiar with aphids, slugs, snails, mites and scale insects but mealy bugs are
less commonly seen under normal garden conditions.
Mealy bugs have an unusual
appearance. They are covered with a white powder and fine white hairs. They
feed by sap sucking and leaf rasping and may be quite debilitating if present
in large numbers.
Probably the most common disease
is sooty mould caused by a fungus that grows on the honeydew secreted by
feeding insects. The cure for this involves first removing the insects and then
spraying with a fungicide, such as mancozeb, to halt the mould.
Most other fungus problems, such
as root rots and leaf spotting, can be traced to poor growing conditions,
especially overwatering and poor ventilation.
Orchids may also become infected
with viruses. These often appear as unusually marked patches on the leaves,
flowers or stems or may simply result in stunted growth. Nothing can be done to
cure virus infected plants so if badly affected they are best got rid of.
Orchid Selection
There are hundreds of orchid genera, many very closely allied to one another. The following is a selection of a few of the more commonly grown.
Bletilla
The ‘Chinese Ground Orchid’ (B. striata) is a hardy
deciduous species. Remarkable for its ease of cultivation rather than its
flamboyance. Will grow in any moist garden soil in light shade. Magenta to
purple flowers from spring.
Cattleya
Spectacular and reasonably tough plants. They are easy for
beginners and often represent the next step after Cymbidium. Cattleya
is a mainly epiphytic genus and develops large pseudobulbs that enable the
plants to withstand some drought. They prefer to dry out between waterings and
prefer lightly shaded conditions.
Coleogyne
A large genera many of the species of which are fairly hardy
and may be grown outdoors in genuinely frost free areas. Most need cool summer
temperatures and are an ideal choice for a shadehouse. They prefer light shade
and shelter from winter rain. Usually flowers from late winter.
Cymbidium
Without doubt the most widely grown orchid genera. Tough and
adaptable Cymbidium is the ideal choice for the beginner. Plants are
available in a huge range of colours and flower patterns. Able to tolerate
extended periods with overnight temperatures of 5°C and drought tolerant. It’s
very hard to kill a Cymbidium but they do so much better when looked
after.
Capable of being grown outside year round in many areas.
Medium to high light levels are preferred. The soil should be allowed to dry
between waterings in winter but should be kept moist when the plants are in
active growth. Feed regularly. May flower at any season but usually from late
winter to late spring.
Dendrobium
There are native species but those commonly grown are
exotic. They require reasonably warm nigh temperatures; preferably not below
12°C. Most develop conspicuous pseudobulbs and produce their flowers on long
canes.
Epidendrum
The common ‘Crucifix Orchid’ (E. ibaguense) is the
best known of this genus. Most species will tolerate some frost and are good in
shadehouses. Not spectacular but unusual. The aerial roots are a feature.
Rather tall but excess growth with aerial roots can be removed and grown on. No
pseudobulbs.
Laelia
Mainly epiphytic orchids that will tolerate cool conditions.
Most species will grow outdoors if frost free. Prefers light shade and should
be allowed to dry between waterings. May be grown on bark slabs. Many of the
species flower in autumn and winter.
Lycaste
Easily cultivated epiphytic orchids. Their culture is very
similar to Cymbidium. They prefer cool summer temperatures and will
tolerate winter lows of 5°C. Allow to dry in winter but keep moist in summer.
Some of the species are deciduous. The long strap-like leaves can become untidy
and are easily damaged.
Masdevilla
These epiphytic orchids prefer low to medium light levels
and high humidity. Best in cool even temperatures; winter lows of around 5°C to
summer highs of not more than 23°C. Some species do well outdoors in genuinely
frost free areas. They prefer even moisture throughout the year but must not be
overwatered. This genus does not produce pseudobulbs.
Pleione
Often grown in pans in alpine houses and capable of standing
some frost. The flowers resemble Cattleya but the plants are considerably
smaller. Fully dormant in winter. Plant in gritty soil and water and feed once
actively growing.
Odontoglossum
Not too demanding but intolerant of very bright conditions.
Able to tolerate overnight winter temperatures of 8°C or slightly lower. They
like cool daytime temperatures. Often better in a shadehouse over summer. Allow
to dry in winter but keep moist when growing. May be grown on bark slabs.
Oncidium
A very complex grouping of related genera. They require
bright conditions and winter lows of not less than 10°C. The flowers are
spectacular and freely produced on healthy plants. Miltonia is a closely
related genus. Many intergeneric forms exist.
Paphiopedilum
Commonly known as the slipper orchid due to the flower’s
prominent pouch. Easily grown but many require warm conditions with
temperatures above 15°C. The tougher species will tolerate 8-10°C for short
periods. Day temperatures should be below 25°C. This narrow temperature range
is the main barrier to success. They prefer low to medium light and should be
kept moist throughout the year.
Phalaenopsis
The ‘Moth Orchids’ demand warm temperatures with winter
minimums of 15°C although they will tolerate 12°C or lower for brief periods.
They prefer low to medium light and high humidity. They need plenty of air at
the roots and are best grown in baskets in a very coarse mix.
Vanda
Often tall plants with very prominent aerial roots. Some
species will tolerate winter lows down to 8°C but most are more tender. They
prefer bright light and plenty of summer moisture but they should be allowed to
dry over winter. High humidity is preferable. Stems with aerial roots may be
removed and grown on as new plants. The best known species V. coerulea
is autumn to winter flowering and one of the hardiest.
Copyright Geoff Bryant
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