Description & Interesting Facts:

Paphiopedilum, often called “Lady's Slipper” is a genus of the orchid subfamily Cypripedioideae, of the flowering plant family Orchidaceae. The genus is native to the tropical forests of Southeast Asia, the Indian Subcontinent, southern China, New Guinea and the Solomon and Bismarck Islands. In their natural habitat they grow as terrestrials on the forest floor, flourishing among the layers of humus, and some are lithophytes and attach themselves to rocks. 

Due to their popularity, Paphiopedilums have been ruthlessly gathered and poached from the wild, making them very rare or extinct there. As soon as a new species or population is discovered, poachers will take the plants and sell them to orchid collectors for large sums of money. Habitat destruction also contributes to their rarity.

The flowers are waxy and long-lasting, and are usually yellow, orange, red, or purple with contrasting spots. They are considered to be highly collectible by orchid growers due to the curious slipper-shaped lip (labellum) of the flower which serves as a trap for pollinating insects seeking nectar by forcing them to climb past the reproductive structures to fertilise the flowers. Unlike most other orchids, the flowers characteristically feature two fertile anthers (male, pollen-producing structures) instead of just one.

Depending on the species, the blooming season for Paphiopedilum orchids can start in autumn and goes through spring, or from spring to midsummer. Some produce new growths year-round and flower as each growth matures. Lady’s slipper orchids make excellent pot plants that are attractive even out of bloom and the flowers can last for up to three months.

Most species have rhizomes and fibrous roots that are thick and fleshy; and potted plants will form a tight clump of roots that, when untangled, can be up to 1m long.

Paphiopedilum orchids are divided into two main groups. The first group is called “mottled-leaf” and the second is called “strap-leaf multiflorals”.

Lady's Slipper Orchid Image by Isabela Cocoli from PixabayMottled-leaf Paphiopedilums

Mottled-leaf species have beautiful foliage that is sometimes compared to a marble-like pattern. These are the warm-growing lady’s slipper orchids which prefer warmer conditions, and can happily spend the summer outdoors in a suitably shady spot.

Strap-leaf Multifloral  Paphiopedilums

Strap-leaf multiflorals have solid green foliage and also have the ability to produce many flowers all at once. These cool-growing species and their hybrids should not be placed outside in the summer unless the temperatures are always cool.

There are thousands of hybrids in a range of colours, shapes, and sizes, all of which have the characteristic slipper-shaped lip.

Cultivation:

Although the different species identify as either warm or cool growing, and their care differs slightly, many orchid growers successfully grow both the warm and cool species under the same growing conditions. To be safe, ask your grower for specific advice for your lady’s slipper.

How much light do lady's slipper orchids require?

Indoors:

Because these orchids are tolerant of low light and shade they are easy to grow in lower light areas of the office or home. If you need some extra light, grow lights or fluorescent lighting works well. Suspend lights about 30cm above the foliage.

An east facing window where the plant receives some early morning sun would be perfect.  A warmer north or west facing spot could also work as long as the plants are protected from strong sunlight by sheer curtains.

If the leaves of your plant are too pale or yellowish, the plant could be getting too much light.

Outdoors:

Outdoors, some varieties of these terrestrial orchids prefer full sun in the morning with afternoon shade. Other varieties prefer only dappled sun throughout the day.

Because lady’s slipper orchids are woodland plants they prefer cool sites which do not become too dry and hot during summer. Semi-shade, with no direct sun at midday is ideal, and places on the south side of the garden, where ferns would also thrive would be perfect.

Don’t plant your slipper orchids to close to trees or big shrubs because their roots will be competing for water and nutrients.

Are lady’s slipper orchids hardy to cold?

Some species of lady’s slipper are completely hardy and no protection during winter is required, as they have adapted to temperate climates by becoming deciduous and dormant during times of inhospitable weather.  Many of these species require several months at near-freezing temperatures to become "vernalized," i.e., brought to the condition they are normally in at springtime, so that they can produce leaves.

However, once they have started growing, the leaves are sensitive to frost. Protect the plants by covering them with pots or buckets if there is any danger of late frosts or snowfall once growth has started.

What are the optimal temperatures for growing lady's slipper orchids?

The warm-growing lady slippers with mottled foliage thrive in daytime temperatures between 23 and 30°C, and night time temperatures from 15 to 18°C.

The solid green-leafed types come from higher, cooler altitudes, and require temperatures between 22 and 27°C during the day and 10 to 16°C at night.

These are recommended temperatures, but many growers are successful at growing both types in the same temperature range.

Modern hybrids are typically easier to grow in artificial conditions than their parent species, doing well indoors with temperatures between 13 and 26°C.

How much humidity do lady's slipper orchids require?

Outdoors most species thrive in moderate to high humidity of 40 to 70%. Indoors a moderate humidity of 40 to 50% is adequate.

Why do orchids require humidity?

Humidity is the percentage of water vapour in the air and you have most likely observed that humidity is lowest during the day and highest in the evening and morning. Orchids, like all plants have stomata or pores on their leaves that allow them to breathe by absorbing carbon dioxide and releasing oxygen. So, when orchids open their stomata to breathe they lose water, and in their native rainforests, humidity compensates for the water lost when opening their stomata.

If humidity levels are too low this means that the water loss through the stomata is greater than the water absorbed through the roots, resulting in a drought situation. In response to low humidity levels, the orchid closes its stomata and stops absorbing carbon dioxide. In essence, it stops breathing!

Orchids require water vapour in the air, and you cannot compensate for a lack of humidity in the air by increasing water to the roots.

If you live in our humid subtropical regions orchids will thrive indoors or outdoors with little effort. However, in colder, less humid regions of the country will they need some extra TLC.

Lady’s slipper orchids require a minimum of 45 to 50% humidity indoors, and if you live in an arid summer rainfall region, it may be best to increase the humidity level in your orchid room year-round.

How to increase humidity indoors and outdoors

It’s easy to increase humidity outdoors and in a greenhouse by turning on misters, and in a greenhouse you can just spray down the floor for higher humidity.

Group plants together

Grouping pot plants together indoors increases humidity around the plants, creating a mini microclimate, but take care not to overcrowd the plants, giving them sufficient space so air can move freely around them.

Make an orchid humidity tray

One popular way to increase humidity is to make a humidity tray for orchids. Simply find a drip tray or any watertight bowl that you can fill with small pebbles or gravel. Pour water into the tray until it is about halfway full and the orchid pot can stand safely on the gravel above the water line, and not in the water.  If an orchid’s roots sit in water they will rot and die. This method allows the water to evaporate and creates a small microclimate around the plant.

Does hand misting increase humidity

Orchids and particularly those that are mounted will benefit from regularly misting of their roots, but not really their leaves. In fact, misting orchid leaves to frequently indoors can lead to infection if there is little or no airflow.

Hand misting around the plant is also only a temporary fix and will not raise the humidity levels around the plants for long.

Use a Hygrometer and Humidifier

If you live in a dry region purchasing a digital indoor hygrometer which measures both temperature and humidity would be a worthwhile investment if you wish to grow orchids indoors. You can purchase these at any local home goods store or online.

When using a humidifier, follow the manufacturer’s instructions to ensure that undue moisture does not accumulate. If your windows and mirrors have condensation this is a sure sign that the humidity is too high.  To reduce fungal and bacterial growth, keep your humidifier clean. Follow the manufacturers’ instructions as regularly cleaning your humidifier will reduce the amount of fungus and bacteria in the air. Purchase a humidifier with the largest water tank that you can afford. This will reduce the number of times that you will have to refill the tank.

Why orchids need good air flow

If you are serious about growing orchids you need a fan, as airflow is the counterbalance to humidity. Orchids need humidity to breathe and, just as importantly, orchids need good air movement to stay healthy. Disease, mould, fungus, and bacteria all have a harder time taking hold of your orchid with a steady, yet gentle airflow around them. Together, humidity and airflow will create a healthy climate for orchids.

If you only have only one orchid, opening a window may be sufficient, but a small fan is your best option if you have a few orchids. Simply turn the fan to the lowest setting and face it away from the plants as pointing a fan directly at the orchids can be too drying.

What growing medium is best for lady's slipper orchids?

Indoors:

The potting medium must be a special mix for terrestrial orchids. A well-draining orchid mix containing materials like bark, sphagnum moss, and perlite would be perfect.

Avoid using regular potting soil.

Outdoors:

Basically, these orchids and their hybrids prefer a well-aerated, crumbly soil structure that is at least 10cm deep, and with medium moisture conditions. Dense and loamy soils have to be improved with mineral materials such as crushed clay pebbles or crushed lava (available from bonsai growers and aquarium stores). If the planting site is too wet, a drainage layer with crushed clay pebbles or crushed lava should also be added.

In winter rainfall regions the plants will need protection from constant winter dampness with a well-ventilated rain cover, or by planting into a pure mineral soil mix. Otherwise, there may be losses due to rot.

In sandy soils, which dry out rapidly, it is recommended to increase water retention by mixing in perlite. 

Mulching the soil regularly with a layer of organic material like fallen leaves and small twigs will have a favourable effect on the structure of the soil.

How to plant slipper orchids in garden beds?

Spread out the roots in the upper 10cm of the soil, with the rhizomes about one inch below the surface and the shoot buds facing upwards. Fill in the remaining substrate without compressing it, and water thoroughly.

How to water lady’s slipper orchids

Lady’s slipper orchids don't have pseudobulbs that store moisture, so they must be kept constantly moist throughout the year, but not soggy. The growing medium for potted specimens, and for those growing in garden beds,  should never be allowed dry out completely, therefore in dry summers careful watering is recommended.

Always use tepid water as freezing cold water will shock the plants. Avoid hard or heavily chemically treated tap water, or allow it to sit out for several days before using. Rainwater is best and for indoor specimens filtered water would be good.

How to fertilise lady’s slipper orchids

Good results may be obtained by using a general purpose fertiliser as well as fertilisers high in nitrogen all year round. In garden beds you can use any granulated commercial garden fertiliser, but slow-release fertilisers are best for their long-term effect.  After flowering the need for nutrients is much lower.

Beware of over fertilising as their fleshy roots are sensitive and easily burned if too much is applied.

To prevent the build-up of salts, flush out the growing medium with filtered water after every fourth fertilising.

Leaf colour is a good indicator of plant health and they should always be a bright green. A yellowish green indicates nutrient deficiency or too much sun.

How often must slipper orchids be re-potted?

Lady’s slipper orchids fare best when not too pot bound, however they do not need large pots, and 15cm pots are ideal. They are intolerant of broken-down potting medium, so repot every two years or so after blooming.

If you do have a lady slipper orchid that has matured to reproduce new stems, it's recommended to keep no more than three stems in one pot.

Gently remove the orchid from its current pot and examine the roots, trimming away damaged or rotting roots with sterilized tools before repotting.

Place the orchid in the pot adding planting medium in and around the roots. Paphiopedilums do not like their roots exposed, so be sure to cover the rhizomes. If aerial roots are present, allow them to grow in their natural direction and avoid trying to force them into the pot.

Water gently but thoroughly and give the orchid several days to a week to recover before continuing regular fertilisation.

Lady's Slipper Orchid Image by Peter Franke from PixabayWhen to cut the dead flower spike

Do not cut the flower spike until all flowers have finished blooming and the spike turns brown.
Some species and hybrids are of the sequentially flowering paphiopedilums and can be in bloom for over a year! After your orchid has completely finished flowering cut the spike off where it emerges from the plant.

Propagation:

The species and their hybrids are extensively cultivated, but orchids of this genus are notoriously difficult to propagate by tissue culture and today commercial cultivation is almost exclusively seed-based. This means every plant is unique.

Problems, Pests & Diseases:

Slugs

Slugs can wreak havoc within one night, and particularly during springtime, so special protection is indispensable. The safest methods for controlling slugs are a slug fence or a barrier consisting of a vertically mounted copper plate.

Mealybugs

Mealybugs are the most common pest of lady’s slipper orchids, identified by small, white, cottony webs on the undersides of leaves. Gently swab affected areas with a cotton bud dipped in isopropyl alcohol.

Botrytis petal blight

Small dark spots or patches that develop on flowers indicate botrytis petal blight. This is usually the result of too much humidity or poor air circulation. Remove affected parts and try installing a fan or relocate the orchid to a brighter location.

Yellowing leaves with black spots

This problem can crop up when the orchid is exposed to cold or wide temperature fluctuations.

Dry or dark leaf tips or edges

The orchid may be sunburned. Be sure to place it where it receives only dappled, indirect light.

Stunted growth or sudden flower loss

Always use lukewarm or room temperature water. Cold water can damage roots.

Toxicity:

Paphiopedilum and their hybrids have no reported toxicity to birds, cats, dogs, horses, livestock or people.