Phalaenopsis: How to Grow Moth Orchids in Australia

What are Phalaenopsis?

Moth orchids, the common name for Phalaenopsis, make up a genus containing around seventy species of flowering orchids. Every plant in the genus is either an epiphyte or a lithophyte, meaning they cling to rocks, crevices or tree bark for stability, while feeding from humidity and rainfall.

As the plants develop, they can create divisions of themselves from their roots, or by rooting from old flowering stems (if you grow orchids at home, this is the easiest way to propagate new ones, as the new rosettes of foliage usually begin to root into the air).

Some moth orchids, like Phalaenopsis philippinensis, have dense flowering stems, with over thirty flowers, all in bloom at once. Others have as few as two or three flowers at any one time, but tend to flower over a long period, and repeat flower more reliably after deadheading.

Natural Habitat of Moth Orchids

Phalaenopsis are native to Australia, New Guinea, China, Taiwan, India and Southeast Asia, but the densest and most varied habitats are found in Indonesia and the Philippines. 

In all cases, they have tropical or subtropical levels of humidity. Providing that at home can be difficult, particularly in southern Australia, but it is very much possible, and if you get it right, moth orchids are actually pretty simple plants to grow.

Main Groups and Types of Moth Orchids

There are seventy species of moth orchids, and most are sold as true species varieties, rather than cultivated or hybridised plants. Those seventy species fall into four subgenera; 

• Phalaenopsis subgen. Phalaenopsis
• Phalaenopsis subgen. Parishianae
• Phalaenopsis subgen. Hygrochilus
• Phalaenopsis subgen. Ornithochilus

Each group is distinct in flower shape, stem length, colouration and in how it roots, but there is some confusion about how and where to place each subgenera in relation to each other, with multiple former subgenera now grouped in with the main four.

When it comes to identifying moth orchids, it’s generally simpler to stick to the species, as even within groups, colourings can match other subgenera more closely.

Native Moth Orchids

There are over seventy species of moth orchids and many have naturalised in Australia, but only one is truly native. Phalaenopsis rosenstromii is the Australian native moth orchid, and is easily recognisable thanks to its unique petal structure, and vividly crisp white colouring. 

The two true petals (the forwardmost petals on either side) are distinctly diamond shaped, with sharply pointed triangular sepals beneath them. The top sepal is indistinct, with a simple curved shape, but the lip (which guides pollinators to the bright yellow throat) is often loosely curled inwards.

P. rosenstromii is found in the wild in north-east Queensland, and should only ever be grown from cultivated stock, not collected from the wild in any form. Over collection does threaten the species in nature, so make sure you find your native moth orchids from reputable sources.

Best Moth Orchid Varieties to Grow in Australia

The native moth orchid, P. rosenstromii, is the best choice for any Australian home, and any tropical-subtropical gardens, but we thought we’d give you some further inspiration for other tropical and subtropical moth orchids that will do well indoors in any part of the country.

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How to Grow Phalaenopsis in Australia

Moth orchids need tropical conditions, so growing them outdoors in most parts of southern Australia simply isn’t a possibility, but they can be grown in glasshouses, conservatories, and in hot summers, do seem to benefit from a few weeks outdoors.

Our guide focuses on how to grow moth orchids indoors, but we’ll share some tips on how to adapt your outdoor growing conditions to give moth orchids the best possible chance.

Growing Moth Orchids Indoors

Moth orchids grow best indoors, as it’s simpler to control their light, temperature and humidity, but it’s important to avoid common mistakes, like overheating, or over ventilating them. 

Essentially, you just need a good free-draining orchid potting mix (usually made up of bark with some crushed charcoal to prevent bacteria) to grow moth orchids successfully. However, finding the right conditions in your home can be tricky.

As long as you provide your moth orchids with bright light throughout the day, and protect them from direct sun from around midday to 4 pm, in a room with just above average humidity, they will grow and flower well.

Moth Orchid Pots

In nature, moth orchids grow with their roots exposed to the light, hanging from trees, or clutching onto rocks, so clear pots are essential to grow them well. If you can get your hands on perforated pots, that’s better still as this will allow the roots of your moth orchid to breathe, and make sure there are never anaerobic conditions for water to stagnate. 

Best Potting Mix for Moth orchid

The best potting mix for moth orchids is bark and charcoal. They don’t need any special treatment or amendments, so you can buy any bark-based orchid mix and use it straight from the bag whether you’re planting a cutting or potting up a mature moth orchid.

Humidity Requirements

Moth orchids can cope with a relative humidity of just 40%, but do best in higher humidity paired with ventilation. Ideally, an open window with humidity between 60-80% should be provided.

In closed rooms, 60-65% is the average relative humidity in most homes, so either a ventilated bathroom, or ventilated room with a humidifier is best. (See our review of the best humidifiers here.)

Light Requirements

Moth orchids need bright light and reasonably high temperatures, but don’t cope well if they are exposed to direct afternoon sun. Either place them directly in an east-facing window, or 1-2 m from a bright North facing window. 

Wherever they are planted, you can protect moth orchids from afternoon sun by placing them amongst other house plants for dappled shade (this will also help to hold more humidity in the air around them).

How to Grow Phalaenopsis

Growing moth orchids outdoors is much trickier, as they require temperatures of at least 19-20°C all year round, and can just about cope down to 16°C at night. Through summer, they prefer much warmer temperatures of 25-30°C.

That means that for anyone in southern Australia, and most of Central or Western Australia, they will need to be grown in a greenhouse, under glass, or in a conservatory, where their temperatures are properly regulated.

In those conditions, humidity should be reasonably high anyway, but leaving a few buckets of water around, and occasionally wetting the floor will help to maintain humidity.

Other than that, their growing conditions are the same as if you grow moth orchids indoors; bright, indirect light; allow the potting mix to dry between watering; reasonable humidity; occasional feeding.

Propagating Phalaenopsis

There are, in theory, three ways to propagate moth orchids, but all require some degree of patience. Patience while waiting for divisions to be possible; patience waiting for pollination and germination; or patience waiting for flowering, which can take over three years when propagating from seed or keiki.

How to Propagate Moth Orchids from Division

Personally, I prefer propagating moth orchids from simple divisions, as they flower faster and it helps the overall health of the parent plant to make sure it has space to continue in its current pot. 

This method is really simple, as division means taking a young plant that has generated itself from the base of an existing orchid, usually with roots already in place.

1. Start by gently teasing the roots of the new set of leaves away from its parent (try not to damage the main plant or its roots).
2. Plant the divided moth orchid into a small, clear, pot, filled with a bark-based orchid mix.
3. Water and feed both plants as normal.
4. Position the divided plant next to its parent for a few weeks to reduce any additional shock.
5. Avoid changing its environment until its roots have established well.

Propagating Phalaenopsis from Keiki Cuttings 

Keiki are asexually produced orchids. Where flowers aren’t pollinated, if there is sufficient heat and humidity, the flowering stem can produce a clone of the parent plant. This clone will develop with a small rosette of leaves before putting out its own aerial roots. 

This can be cut from the main plant, and planted into a bark-based orchid mix to create new plants instantly. Once you’ve separated the keiki and planted it in its own pot, it can take over three years before it flowers, so patience is a must!

Note: Leaving these plants on your moth orchid won’t harm the parent plant, but it does make it look messy unless it’s a drooping variety of moth orchid, and it will need very regular misting to provide it with a separate water supply.

Propagating Moth Orchids from Seeds

You can buy moth orchid seeds from most garden centres these days, and you can thank the unquenchable desire for experimentation of houseplant growers for it. Seed germination will, however, take between three and nine months, and generally requires sterile orchid compost, agar gel, and very specific nutrients.

To germinate orchid seeds the proper way, you’ll need to understand what each ingredient is for:

• Agar gel: Extracted from seaweed as a vegan substitute for gelatine. Agar gel provides a sterile and stable growing medium for orchid seeds, which require naturally occurring but established mycorrhizal fungi to germinate in the wild. Agar gel also provides zinc, copper, iron and manganese to support germination.
• Boiled water, cooled: The seeds are very susceptible to infection, rot, bacteria, and fungi, so sterile or distilled water is essential.
• Petri dish: This allows germination in a controlled space (you can buy orchid agar already in petri dishes).
• Hydrogen peroxide: A safe way to sterilise the seeds. This is simply dropped (literally, maximum of two drops per petri dish) into the agar before or during sowing.

Basically, as long as your moth orchid seeds are sown directly onto the surface of the agar gel, in a sterile container, and are swilled with hydrogen peroxide first, they should germinate. After sowing, swirl the petri dish around so seeds are well distributed, and then seal to keep humidity in it (tape the edges if it’s not airtight).

After about three months in a warm spot with indirect sunlight, there should be signs of germination, but wait until the roots are about 1 cm long. Then fill a tiny pot (maximum 4 cm diameter) with a fine orchid bark and crushed charcoal. 

Rinse the roots with cooled boiled water or distilled water, then plant them gently into their growing medium. For the first few months, keep them somewhere bright with protection from any afternoon sun, and water them with clean water.

These young plants can take up to three years before flowering for the first time, but considering each orchid flower can produce thousands of seeds, it’s well worth it for the amount of new plants you can potentially make.

Caring for Phalaenopsis

Once you’ve got the right spot for your moth orchids, the rest is pretty straightforward. Maintain the light levels and humidity, and respond to the plant. If you can do that, there’s very little that can truly go wrong.

Watering Moth Orchids

Water your moth orchids about once a week, either by dipping the pot into water and draining it or by watering until it runs out of the base. In the right conditions, that means doing the same again next week, and the week after that, but if light levels are low, or seasonal changes affect the temperature, your orchid may dry out faster, or slow.

Avoid watering orchids when their potting mix is still moist.

What Fertiliser to Use

When you feed moth orchids is determined by their flowering cycle. Some moth orchids will flower just once a year, so feed them from spring to late summer, or until they finish flowering. Others flower repeatedly when grown indoors, so will need feeding at least monthly with a diluted orchid feed.

Pruning Moth Orchids

Moth orchids don’t technically require pruning, but once the flowers have dropped, the stem will either die back, or develop a new set of leaves from where it flowered, also known as a keiki (an asexually produced baby orchid).

Unless you plan on building a collection, and have several years to wait for your keiki to grow into a flowering orchid, it's best to prune old flowering stems right down to the base as they will just fade and look untidy.

Cutting spent flower stalks back can also encourage repeat flowering on new stems in a few weeks’ time (though in our experience, this is 99% luck and 1% skill).

Repotting 

Moth orchids root quickly into their new pots, and as soon as you get a young moth orchid home, you should plant it straight into a bigger pot. For any other moth orchids, if their roots are expanding the pot, or growing in rings around the base or sides of the pot, they need repotting. 

Usually orchids need repotting every two years, but some slow growing varieties can be quite happy in the same pot for a decade or more, so just keep an eye on the roots, and pot them on into a new, slightly larger clear pot when they need it, using the same potting medium they were in originally.

Common Moth Orchid Pests and Diseases

Moth orchids are very resilient plants, and if you grow them in the right growing medium with proper watering they shouldn’t ever suffer from pests. Spider mites and mealybugs can be a problem for overly damp, or overly dry orchids, but you can fix that by rinsing your moth orchid and its roots gently in the sink before repotting into a clean orchid medium.

Moth orchid diseases are limited to common viruses and fungal problems like botrytis and anthracnose. Proper care will prevent this entirely, and planting in a perforated clear container should stop any possibility of collar rot or root rot.

Phalaenopsis Frequently Asked Questions

What to do when a moth orchid has finished flowering?

When a moth orchid has finished flowering, you can cut right back to the nearest unopened bud. This will trigger repeat flowering in most cases. If the entire stem has finished flowering and shows no sign of new growth, cut the stem right back to the base.

How long do moth orchids last?

Moth orchids last for years, and can be with you for your whole life with proper care. Their flowers last for around three months, making them an ideal houseplant for beginners, who can simply water and feed them once blooming is over until a new flowering spike shoots up.

Do you water moth orchids after the flowers fall off?

You should water moth orchids even after flowers fall off. The orchid will continue to grow and develop, and its roots and leaves are still actively growing. If the temperature drops through winter, they may enter a brief dormancy, so reduce watering slightly then.

How do I get my moth orchid to flower again?

A few weeks with cooler nights will trigger a moth orchid back into flower. This is because the cooler evenings and nights will trick the orchid into thinking it has experienced a winter, triggering new growth and flowers when it returns to its normal warmer position.

Will moth orchids grow if all their leaves fall off?

Moth orchids need some leaves to continue growing, as they develop new shoots, and new leaves, from the old ones. If all leaves are lost they will simply stop growing, so act quickly if young leaves begin to drop from moth orchids.

Should moth orchids be watered from the top or bottom?

Moth orchids can be watered from the top, from the bottom, or even by placing ice cubes in their pots to water slowly as they melt. I prefer to submerge moth orchids in perforated pots entirely in water once a week, then drain them. 

Is tap water OK for moth orchids?

Tap water is fine for mature moth orchids, but water in some areas has chemicals and salts that can harm them. Any damage from tap water will be visible within a week, so if you try it once and your orchid responds badly, boil or freeze your water before use to sterilise it.

Looking for more orchids to grow? Check out our guide to growing Cooktown orchids for more options.