Growing orchids at Kew

Growing Orchids

how it is done at The Royal Collection

It is the aim at Kew to maintain a selection of orchids that is as large and diverse as possible. The plants are in constant use for display and research of various kinds and their role in conservation and in the propagation and reintroduction of rarities is becoming increasingly important. In this chapter some features of the greenhouses, processing introductions and composts relating to the orchids at Kew are recorded.

Glasshouses Introductions and Accessions Composts

The Reserve Collection of orchids presently occupies 862 square meters of glasshouse space in the Lower Nursery, a complex of greenhouses that is not open to the public. It is used for holding and propagating the tropical plant collections, and within it the orchids fill five large glasshouses and a separate seeding house. Some of these houses are partitioned, so there is a total of eight different growing environments. They have been controlled, since 1985, by a Van Vliet CR90 Environmental Computer System which was installed at the suggestion of Sir Robert and Lady Sainsbury. This generous donation provided Kew with one of the first computerized systems in use for orchid growing. It allows for very precise control of temperature, relative humidity, ventilation and air movement throughout the day. A sensor in each glasshouse constantly monitors the temperature and relative humidity and, if these vary from the values required, the computer brings into play the equipment needed to change them. Back-up, in case of a breakdown of any of the equipment, is provided by a system of alarms which ring if the temperature in any glasshouse drops below the acceptable minimum.

Heat is provided by piped hot water from natural gas-fired boilers. There is a separate, oil﷓fired system for use in emergency or if the gas supply should fail. All the glasshouses are shaded in summer, either with slatted exterior or interior blinds or shade cloth as well as with 'Summer Cloud 'painted on the glass. Additional cooling is effected by the use of ventilators. Under-bench mist lines and overhead humidifiers are used to keep the relative humidity high. They need to be used more often when the temperature rises, especially if the ventilators are open, as humidity would otherwise drop rapidly. Air movement in each house is maintained by fans and ventilators. The speed of the fans is linked to the temperature and they are programmed to switch off when the vents are wide open. Computer control of these variable factors in the glasshouse environment saves growers' time and, by enabling more precise control of the growing climates, effects a saving in energy consumption even when the nursery is not manned. Regular printouts and graphs of the features of each glasshouse climate enable fine adjustments to be programmed into the system to achieve exactly the climate that seems to suit each group of plants. A summary of the different glasshouse environments at Kew is presented below. The minimum temperatures given refer to winter nights; a day lift of 5º C (8-10ºF) is always given.

1   Warm (House 31, warm, wood and glass).
   18ºC (64ºF) minimum, 32ºC (90ºF) day maximum,
   ventilated at 26ºC (79ºF). Very light.
   For low altitude monopodial genera, Vanda
   Angraecum and others, also low altitude Dendrobium
   species in sections Ceratobium and Phalaenopsis and
   the warm-growing Cymbidium species.

2   Warm (House 39, aluminum and glass).
   17-18ºC (64ºF) minimum, 28-30ºC (82-86ºF) day
   maximum, ventilated at 25ºC (77ºF). Shady and
   humid.
   Used for Paphiopedilum (warmer growing species),
   Phalaenopsis, tropical terrestrials and some African
   epiphytes.

3   Warm-intermediate (House 36, warm,    wood and glass).
   15-16ºC (59-61ºF) minimum, 27-30ºC (81-86ºF) day
   maximum, ventilated at 21-23ºC (70-73ºF).
   For most low and intermediate altitude tropical
   epiphytes, such as Coelogyne, Maxillaria,
   Bulbophyllum and many others.

A mixture of Disa species and hybrids flowers well in the Lower Nursery in mid summer

4   Cool-intermediate, warm day (House 35, aluminum and glass).
   15ºC (59ºF) minimum, 32ºC (90ºF) day maximum in
   summer, ventilated at 25ºC (77ºF). Very light and
   airy. For Cattleya , Laelia and allied genera,
     soft cane Dendrobiums and a wide variety of African
     epiphytes and terrestrials.

5   Cool-intermediate, cool day (House 36, cool, wood and glass).
   14ºC (57ºF) minimum, 25ºC (77ºF) day maximum,
   ventilated at 18ºC (64ºF).
   For mountain species, high altitude terrestrials and
   epiphytes from the tropics particularly Central and
   South America, including Odontoglossum , Lycaste ,
   Coelogyne and Pleurothallids.

6   Cool (House 31, cool, wood and glass). 11ºC (52ºF) minimum,
ventilated at 16ºC (61ºF). For Cymbidium hybrids and Zygopetalums.

7   Cool (House 42, cool, aluminum, glass and melanex).
   13ºC (55ºF) minimum, ventilated at 19ºC (66ºF). 40%
   shade in summer.
   For epiphytes and terrestrials of cooler latitudes
   including some Cymbidium species, cool-growing
   Paphiopedilums, winter-growing Australian and
   South African terrestrials including Disa species and
   hybrids.

8   Cold (House 42, cold, aluminum, glass    and melanex).
   5ºC (41º F) minimum, ventilated at 12ºC (54ºF).
   Most of the terrestrial species from southern Europe
   are grown in this house which has less shading (40%
   in summer) and more ventilation than the others. It
   is also used for cool-growing orchids from Asia,
   including Pleione, Calanthe and Cypripedium.

Many of the orchids will grow and flower well in more than one of these environments, but others have been found, by trial and error, to be quite specific in their requirements.
The orchids are cared for by the Supervisor of the Orchid Unit, who has a staff of three to maintain the collection and at least one student of horticulture. The student receives three months of training in orchid culture as part of a three-year diploma course at Kew and is an invaluable addition to the team.

Glasshouses    Composts Go to the top

Introductions and Accessions

On average about 1,000 orchid plants arrive at Kew each year, some from nurseries or other collections within Britain but most from overseas. First, the documentation is checked. Sometimes the necessary papers become separated from parcels in transit and strenuous efforts are made to ensure the relevant permits or certificates are available or can be traced. No accessions are made until the required documents are available when details are entered in the computer records for each item.
Unpacking boxes of new plants is done with eager anticipation. First the plants are inspected carefully by the specialist Quarantine Officer at Kew, who looks for any signs of pests, such as scale insects, or disease damage, such as the mottling caused by Cymbidium Mosaic Virus. This is a necessary precaution to avoid the introduction of pests and diseases, possibly new to Britain, into the collections at Kew. If any insects are found they are removed and sent to laboratories of the Ministry of Agriculture, Fisheries and Food for identification and advice. (A significant number of invertebrates are forwarded by MAFF to the Natural History Museum for inclusion in its collections. just like the plants, the associated creatures are of scientific value, and several come into Kew each year which prove to be undescribed or little-known species.) Diseased leaves or roots are removed and may also be sent to MAFF laboratories for identification of the pathogen. Subsequently, plants are treated effectively or destroyed. The majority of orchids sent to Kew are clean, healthy and in good condition, but if they are desiccated or damaged when they are received this is noted before they go any further. It may be useful information if the plants do not establish well.
Detailed provenance data is always requested for incoming plants and consulting field notes enables the horticulturist to establish and maintain the plants in the most suitable way. The notes are often vital to scientists who study the orchid collection and need to know the origin of a particular plant.
After inspection and any necessary period of isolation or treatment, the orchids are passed to the staff in the Orchid Unit. Here it is decided how best to treat them, whether they should be grown mounted on cork oak bark or, if potted, which kind of compost to use. The staff also decide which of the different glasshouse environments would best suit the new plants, depending upon their country of origin and the altitude and conditions from which they were collected. The new orchids are potted up, labeled, placed in the environment that is anticipated will be most suitable and looked after carefully. Within a short time, signs of growth are apparent, usually new roots, but if the plants do not respond well to one set of glasshouse conditions they are moved to another in which they may grow better.
Careful record﷓keeping is very important at Kew. All the information about each plant is stored and must be accessible to all who may need to use it. Each new plant introduced is given a number (its accession number), and entered, first into a book recording all new plants for each year and then on to the computer database. Along with the accession number and the 1 name of the plant, additional information such as the field notes, flowering season and whether herbarium specimens were collected at the same time is recorded. More details can be added at any time in the future, as information about the plant is acquired. Access to the computer database is quick and easy for anyone who needs it in the course of their work.
Every orchid at Kew has a plastic label on which essential and clearly summarized information is recorded. It is inserted in the pot or attached to the medium or mount. Across the top of the label is a three-part accession number. The first part, a three figure number, is the batch number and is common to all the plants collected by the same collector and sent to Kew at the same time. The second, two figure number records the year in which the plant was received at Kew. The third, with five figures, is called the sequence number and is unique to each individual plant within the batch and to any plants which may be propagated from it. Underneath the accession number is the collector's name and number, or the name of the person who donated the plant to the Kew collection.
In due course another line of information is added below the collector's number, the letter W' followed by a date. This refers to the date when the plant, in flower, was taken to the Herbarium for a botanist to identify it or to check its name - a process known as verification, hence the abbreviation. When a plant has been identified or verified, the computer record is updated and information supplied by the botanist, such as the known geographical range of the species and whether it is endangered in the wild, can be incorporated.
The full name of the plant is written on the label as well as the country from which it comes and possibly the altitude at which it was growing.
The back of the label may be used by each grower to record facts and observations which they find useful, such as when the plant was last repotted or whether the flower is a particularly fine form.

Glasshouses Introductions and Accessions Go to the top

Composts

Composts for growing orchids are a subject of great interest, and individual growers enjoy experimenting with slightly varying mixes to find the ones that work best under their particular glasshouse conditions. The style of growing will determine composts to some extent; a very coarse mix is suitable for those who like to water frequently, while a finer mix holds moisture much longer. At Kew the compost mixture is prepared or chosen to suit the size and habit of each plant.
Temperate terrestrials, such as the winter-flowering Australian and South African terrestrials, are grown in a mixture of: 3 parts grit, 2 parts fine bark, 1 part leaf mould and 1 part unsterilised loam.

For the European terrestrials this is modified by adding an extra part each of unsterilised loam and leaf mould to make the proportions: 3 parts grit, 2 parts fine bark, 2 parts leaf mould and 2 parts unsterilised loam.

Rather more leaf mould is added to the mixture for growing plants originating from woodlands, such as Cypripedium calceolus, the lady's slipper orchid, and
Goodyera repens, the creeping lady's tresses. A high content of organic matter is vital for orchids which grow symbiotically with fungi throughout their life, and these include many of the terrestrial species. The fungi live by breaking down organic matter in the soil, and if this is exhausted, or the compost becomes too dry, the fungus will not grow and the orchid cannot thrive.

One group of South African terrestrials, species and hybrids of the genus Disa, is grown in a simple mixture consisting of: 1 part peat and 1 part perlite. Disas grow in or close to running water and this compost not only allows good water-retention but also good drainage. Disas are repotted at least twice every year, as this very peaty compost would otherwise become rather stagnant.

For tropical terrestrials, the grit and loam content of the compost is lower than that used for the temperate terrestrial orchids and the leaf mould and peat content is higher. Many forest and woodland orchids in the tropics have a shallow rooting system, which is limited to the layer of litter overlying the soil. Good drainage is essential.

The genus Paphiopedilum is an important feature of the orchid collection at Kew. For all the species and hybrids the mix contains: 5 parts medium grade bark, 2 parts perlag, 1 part charcoal and 1 part peat. This mixture is modified by the addition of crushed dolomite chippings for Paphiopedilums which grow on limestone in their natural habitats, and by the addition of chopped sphagnum moss for those which are known to enjoy moist conditions.

The Cymbidium compost is rather similar and consists of: 3 parts bark, 3 parts coarse sphagnum peat, 1 part perlag, 1 part perlite, 1 part charcoal, plus a dressing of hoof and horn meal or 5 oz per bushel of Vitax Q4, a balanced general plant food.

Epiphytic orchids are grown either mounted on bark or in one of a variety of pots. Smaller epiphytes are often grown by tying them on to a block of rough cork oak bark with transparent nylon thread. The piece of bark can then be suspended from a wire mesh framework against the wall or from a rafter in the glasshouse and, if misted daily, the orchid will soon put out new roots over the surface of the bark. Firm tying is essential; if the plants are not held tightly against the bark, new roots do not easily adhere to it.

Many epiphytes grow well in pots filled with a standard epiphyte compost made up of: 5 parts bark, 1 part perlag and I part charcoal.
Three epiphyte mixes are used, all having the same ingredients, but in different degrees of coarseness. For small plants a mixture of fine bark, fine perlag and fine charcoal is used. For a very large plant a rather coarse mixture is more suitable. Medium-sized plants are
potted using a medium grade compost. The epiphyte compost is the subject of endless variation as growers like to experiment with a standard compost to make it more suitable for each individual plant. Peat or chopped sphagnum moss may be added to make the mixture more moisture-retentive, while the use of coconut husk fiber makes the mixture more open and fast-draining.

Seedlings which are being weaned from sterile culture need a fine compost which will give their roots good anchorage quickly and also hold just a little more moisture than a standard compost until the young root system grows larger. The ingredients for the typical seedling mix are: 3 parts fine bark, 1 part perlag, 1 part peat and 1/2 part fine charcoal.

This range of orchid composts is subject to change as new products become available. For example, rockwool, a synthetic product used as an insulating material, has been tried for a number of different genera. Many different pots, baskets, wire containers and mounting surfaces are also tried. Ultimately, it is the combination of container, compost and environmental conditions which ensure5 success or failure with orchids in cultivation. At Kew, as in other collections of these specialised plants, there are always some failures, but continuous observation of new accessions and plants which are becoming established, ensures that most of them survive to become permanent additions to the collection.

Glasshouses Introductions and Accessions Composts Go to the top

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