Paphiopedilum - A Guide To Their Culture by Ian Dorman
Paphiopedilums are subtropical plants from South East Asia and are predominantly humus epiphytes, which means that they essentially grow on detritus and mosses in the top layer of the forest floor, lithophytically on rocks and cliff faces, or epiphytically directly on trees. This should be recognised when attempting to cultivate this choice and very diverse genus of orchids. Due to this diversity the following cultural advice can only be of a general nature and it is prudent to research where a species grows in the wild to be able to create optimum conditions for a particular species and its hybrids. There are several good reference books available (listed at the bottom of this page) and the internet is an excellent and quick source of information. See the Links section of this website for many online resources.
The images below give an example of the main subgenus groups of Paphiopedilum. Each type has not only varying growth habits and flower form but may require slightly different culture to truly flourish.
The following cultural notes are primarily aimed at greenhouse growers but also included is advice regarding how some of these plants can be grown in the home. It is important to appreciate that the various conditions for successfully growing Paphiopedilums are interrelated so any changes to one element, for example, light may also have an impact on another, for example, humidity.
There are many recommended substrates or composts which can be used but still by far the most common is a bark based mix. A suitable compost is a mix of bark (60%), large perlite (20%), foam (10%) and sphagnum moss (10%) with some dolomite lime added where the species is known to grow in limestone areas. All these elements should be of horticultural grade and purchased from a reputable supplier. Those new to growing Paphiopediums should initially consider using a proprietary orchid compost available from most garden centres , however as more plants are acquired this becomes prohibitively expensive and unsuitable for some plants.
Although many Paphiopedilum species can experience very low temperatures for relatively short periods in the wild this mainly occurs at altitude in a much more rarified atmosphere than we experience at sea level so there are no truly cool growing species. Often a good rule of thumb is the temperatures we experience in our homes which makes certain Paphiopedilums extremely suitable for home culture.
In order to grow the full range of Paphiopedilums in a greenhouse it is usually necessary to divide the available space into 2 sections; the first section being classed as intermediate with temperature ranges of 14C to 21C in winter and 16C to 25C in the summer months. The second section is classed as warm with a range of 17C to 30C with a warmer minimum temperature in the summer months if possible. The minimum temperatures should only apply at night with a significant uplift during the day required to promote growth and flowering.
Light levels and air movement
Plants should be positioned to receive sufficient light to ensure optimum growth. This will vary according to the species; for example forest floor plants will require much less light than multi- florals which makes them more suitable for home culture. Trial and error is usually the only way of establishing optimum conditions, however it is important to err on the side of caution for all Paphiopedilums which generally require more shade, particularly in the summer months. In a greenhouse suitable shading material should be applied in February or March, preferably externally to provide approximately 70% shade on a warm sunny day.
Where possible gentle air movement should be applied to the growing environment by the use of suitable oscillating fans
Appropriate humidity levels are fundamental to successfully growing Paphiopedilums given the provenance of these plants in nature. In a greenhouse 70% to 80% is required all year round with only a slight tolerance allowed on hot days in Summer. Plants will thrive where light, air movement, temperature, humidity and water at the roots are successfully controlled. It is therefore vital to consider the overall impact of changing one of these elements on the others. There are various ways of maintaining required levels of humidity available to greenhouse growers.
Water, water quality and feeding
Paphiopedilums should be frequently watered during the growing months when light levels and day length are at their optimum levels. Frequency of watering will depend on cultural conditions including pot size. For average size plants these should be watered about once per week in the growing period and about every 2 weeks in winter. Smaller plants in small pots may require more frequent watering. Water quality is important; if using tap water this should be checked for dissolved salt levels and pH. Total dissolved salt levels after the application of feed should be around 500 to 600 microsiemens in the growing months (less in Winter) and pH levels should be less than 7.5. If tap water is not appropriate rainwater can be used instead.
There are numerous proprietary fertilisers available for Paphiopedilums which should be used as per the instructions. Depending on cultural conditions Paphiopedilums can be fertilized all year round with less in the darkest months of the year.
Repotting and dividing
Paphiopedilums can be repotted having outgrown their current pot or when it is decided that the current compost has deteriorated to the point where the health of the plant may be adversely affected. Where repotting is necessary aim to repot the plant into the same size of pot or slightly larger if it has outgrown its current pot. Never over pot a Paphiopedilum. This usually results in the eventual death of the plant due to root loss. After repotting keep the plants much drier for a couple of weeks until it is evident that the plant is growing well again. Some Paphiopedilums, particularly those which grow on rocks strongly resent repotting and special care is required. Paphiopedilums as a rule of thumb and again depending on cultural conditions should be repotted every 2 years. Smaller plants or those which are growing more vigorously may require more frequent repotting.
Paphiopedilums generally resent dividing and may not thrive in the future unless the original plant is mature and at least consisting of 3 large adult size growths prior to division.
Pests and diseases
The 2 main problems affecting Paphiopedilums are mealy bug and bacterial rot. In small collections mealy bug can be eradicated by close inspection of individual plants and the use of rubbing alcohol and a cotton wool bud. In larger collections a suitable insecticide can be applied on a regular basis. Unfortunately systemic insecticides are not always as effective on orchids due to their slower growth cycle or metabolic rate.
Bacterial rot can be extremely dangerous to Paphiopedilums, particularly Erwinia and it is important to take action at the first sign of attack. Removal of affected leaves with a clean knife is the first step, followed by spraying with a suitable fungicide. Many growers use ground cinnamon on affected areas as it seems to have a cauterizing effect.
Paphiopedilums in the home
Certain Paphiopedilums are extremely suitable for home culture mainly those with low light requirements and compact size. Plants should be positioned in a north
east facing window but if this is not possible should be protected from direct sunlight with suitable sun shade. In a home low humidity is usually a problem for growing orchids so this must be supplemented by placing the plant on an upturned saucer inside of a larger saucer containing an aggregate topped up with water. The plant must always sit proud of the water level in the saucer which should be continually topped up as required.
Recommended Beginners Plants
The following species and hybrids are recommended for their relative ease of growing in both greenhouse and home environments - from easiest on the left, to more difficult on the right. However, as any experienced grower will tell you, you may find your experience the total opposite!
Recommended Reference Books
'The Paphiopedilum Growers Manual' by Lance A.Birk
'Paphiopedilum' by Braem & Chiron
'Tropical Slipper Orchids' by Harold Koopowitz
'The Genus Paphiopedilum' by Phillip Cribb