Article by David Marks
This guide to Phalaenopsis Orchids (Moth Orchids) covers watering, feeding, humidity, light levels, what to do when the flowers fade, how and when to re-pot, where and when to buy for best value and health then finally pests and diseases. It is specifically about Phalaenopsis orchids which have different care needs from other orchid types.

 

To navigate around this article about Phalaenopsis Orchids, click the “DETAILED MENU” button above.

All the pictures are of our own orchids. All the information in this article is based on over seven years experience of growing Phalaenopsis orchids in the UK.

INTRODUCTION TO PHALAENOPSIS ORCHIDS

Sometimes also called Moth Orchids, Phalaenopsis Orchids are the most commonly grown of all the orchids by amateurs in the UK. As well as being the easiest to grow, they are also readily available and come in a huge choice of stunning colours. If you are new to orchid growing then this is the one to choose.

Typical flower of Phalaenopsis Orchid

They are only suitable to be grown as a houseplant. If grown in the ground in the UK, the roots and the crown of the plant will rot in a very short time. Neither are they suitable for growing in a greenhouse. The levels of direct sunlight will be too high and the leaves will be scorched. The glass of the greenhouse will only make matters worse.

To identify a Phalaenopsis orchid, first look at the leaves. They should be wide and leathery. Now look at the surface of the compost and you will see the trademark root tentacles randomly growing above the surface. As a final check, there should be no bulbous swelling at the base of the plant.

Click to enlarge. Identify Phalaenopsis orchid

Those new to orchids are often tempted to cut back the roots above compost surface because they look unruly, but this is a mistake. In nature, the roots are used by the orchid to anchor themselves to tree branches. The health of the plant can be significantly affected if the roots are trimmed or cut off. There appears to be a natural balance between the size of the roots and the size and health of the plant overall.

All the care notes in this article are aimed at providing Phalaenopsis Orchids with growing conditions which are similar to those in their natural habitat. These are the conditions which the plants have adapted to and in which they thrive best.

They are native to many areas in topical Asia. They grow on tree branches under the top canopy of trees, out of direct sunshine. They grow best with lots of sunlight but not direct sunlight which will scorch the leaves.

In the times between rainfall, the atmosphere is generally humid, slowly drying out before the next downpour. Because they naturally grow on the branches of trees they have adapted to low levels of nutrients, hence their need to only be fed lightly.

For a detailed and pictorial description of how flower stems, roots and new leaves are formed on Phalaenopsis Orchids, click here. You will see a very detailed step by step growth guide throughout the season which is invaluable for better understanding how the plants grow and can be cared for.

WHEN DO PHALAENOPSIS ORCHIDS PRODUCE FLOWERS?

This is a key question when looking after Phalaenopsis orchids because it has a bearing on when the plants are actively “growing” and when they are “resting”. As can be seen from the sections below, watering, feeding and light requirements differ between the two growth stages. Phalaenopsis do not have a set flowering time of the year, much depends on the heat and humidity in their environment. In general though, they tend to start producing small flower stems (when grown indoors in the UK) in October to November time and start to produce flowers around March time. Flowering can last for a couple of months up to five months.

The start of flower stem production is caused by a drop in daytime temperatures in September, after flowering finishes, but prior to the central heating being turned on in most households. The new flower stem becomes clearly visible (see picture below) a few weeks later.

Difference between flower and root stem
on Phalaenopsis Orchid

New flower stems have a point on the end whereas new roots are rounded. If either appear, it indicates that the plant is actively growing.

HOW AND WHEN TO WATER PHALAENOPSIS ORCHIDS

The key point to note about watering Phalaenopsis orchids is that overwatering will kill  them far quicker compared to under-watering them. They make ideal plants for the forgetful house plant owner! If you forget to water them occasionally they are very forgiving, if you give them too much water the crown and roots will quickly rot.

The rule of thumb is to water them once a week when they are actively growing (see above) and once every ten days when they are “resting”. Our watering method is to fill a large container (about 15cm / 6in deep) with tepid (room temperature) water, place the potted plant in it and leave it there for 5 minutes to soak up some water.

Take the pot out of the water and leave it where any excess water can easily drain away. Don’t let the plant stand in water. Rain water is the best for orchids although untreated tap water is fine. Water that has been softened is definitely not good for them. A small water butt is the ideal solution to collecting rainwater for houseplants.

The alternative is to water thoroughly from above making sure that none remains in the centre of the plant or on the leaves where it can cause rotting.

If you lift a Phalaenopsis Orchid, which is potted in a plastic container, just before it is due to be watered, it will feel very light, it will have exhausted the majority of the water supply in its compost. This is as it should be.

To help understand how Phalaenopsis orchid roots absorb and retain water (and why they do not need a constant supply of water) see the picture below. To avoid damaging our plants we show a rather shriveled root but a healthy root has the same structure.

The picture shows two parts to the root. First the outer sheath which is normally a light grey-green colour. If this is stripped away you will see the thin inner strand of the root. The outer sheath is the part which absorbs and retains water. The thin inner root allows this water to be transferred from the roots up to the main plant.

This is quite a different structure compared to most plants which also have main roots but it is the fine hair-like growths off them which absorb water. Those fine hair like structures have very little ability to retain moisture compared to the fleshy roots of a Phalaenopsis orchid.

HOW AND WHEN TO FEED PHALAENOPSIS ORCHIDS

Orchids need slightly more plant food when they are actively growing compared to a “rest period” which many have for a month or so each year. See here for information on how to determine if  your plants is actively growing.

There is no need to buy special orchid plant foods, normal house plant food will do just fine. Indeed, looking at the NPK (nitrogen, phosphorous, potash / potassium ) ratios in the various orchid feeds available, none of them agree on what is best. Not surprising really, because as far as we are aware, there is no reliable data which indicates that liquid house plant feeds are not fine for orchids, nor is there any solid research to indicate that orchid foods are formulated any better than standard houseplant food.

However, orchids definitely do have low requirements for feeding and we suggest you use one third (33%) of the recommended dose of normal plant food. The best time to add the plant food is each time you water the plant. Water as described above then add the plant food into a small amount of water (half a cupful) and pour it into the plant pot (not into the centre of the plant).

Once every two months when watering your orchid, don’t add any houseplant feed. This will have the effect of washing out any excess salts left by previous feeding and help keep the plant healthy.

LIGHT AND POSITION FOR PHALAENOPSIS ORCHIDS

Your aim as far for light levels is to mimic, as far as possible, natural conditions. Lots of natural light but no direct sunlight between 11.00am and 4.00pm. Direct sunlight onto the leaves of a Phalaenopsis orchid during the middle of the day, especially through windows, can cause them to burn and turn brown.

The best positions for your plant when grown in the house is an east or west facing windowsill. An east facing position will receive light in the morning, turning to shade around mid day onwards. A west facing windowsill will receive sunlight from mi-afternoon onwards. They can be grown all year round in both of these positions.

They also grow well on a north facing windowsill where they will receive no direct sunlight. In this position ensure that the windowsill is fully open to the light and not shaded. We would advise though that you take care to avoid low night temperatures below 8°C / 47°F which can often occur on windowsills in winter. Move the plants away from the windowsill at night if necessary. A combination of cold and draughty conditions is the worst for Phalaenopsis orchids.

The plants will benefit from being moved to a sunnier east / west facing position when the flower stems are fully growing. South facing windowsills can receive too much direct sunlight in late spring to early autumn. Net curtains will reduce the amount of sunlight considerably and are often useful.

CORRECT HUMIDITY FOR PHALAENOPSIS ORCHIDS

Phalaenopsis orchids are probably the easiest type to grow in the dry air found in most centrally heated homes. This is not their condition however and a small amount of additional moisture in the air you can provide will greatly help.

The easiest solution is to permanently stand the potted plant in a tray of water on a sauce or similar which prevents the base of the pot from touching the water. Evaporating water water from the tray will increase the humidity around the plant.

A more attractive solution is to place a layer of pebbles in the base of the tray and add water to just below the top of the pebbles. The potted plant can be placed on the pebbles without touching the water.

INCREASE FLOWERING OF PHALAENOPSIS ORCHIDS

The picture below shows a Phalaenopsis orchid where the flowers are dying. The are slightly limp and in a week or so they will begin to drop off.

At this point you have two choices. The most common action, and probably the most likely to benefit the plant in the long term, is to cut off the flower stem to 5cm / 2in or so above the base of the stem. In this case the plant will not produce any more flowers for four months or more, the natural course of events. Typically, the cooler day time temperatures in September to October will trigger the plant to start producing a new flower stem.

The alternative is to try to force the plant to flower again from the existing flower stem. It won’t produce any more flowers from nodes (see picture above) where flowers have previously appeared but if there are three to four nodes on the lower part of the stem which have not yet produced flowers

To do this, cut the stem just above the highest node where no flowers have yet appeared. This may force the plant into producing more flowers from the existing stem. Sometimes it works, sometimes it fails, but it doesn’t do the plant any harm to try.

There appears to be no obvious reason why some plants produce flowers, at the same time, from almost the nodes (as is the case in the picture above) and others, which produce flowers from only the top nodes, leaving non-flowering nodes lower down.

HOW AND WHEN TO REPOT PHALAENOPSIS ORCHIDS

After a couple of years the growing material in the pot of a Phalaenopsis orchid will have become compacted and it’s a good idea to repot them every two years using new orchid compost. The size of pot is important, about 12cm / 5in wide and deep is the ideal size. If your orchid is in a smaller pot then repot into the recommended size, if it is already in a pot of that size, re-pot into the same size (using the same pot is fine).

For re-potting, use orchid compost not normal compost. Orchid compost has an open structure with larger, woody parts in it. This allows good drainage and is similar to the natural growing conditions. If the compost is dry, wet it a little, squeezing out any excess water.

You are trying to achieve a pot size where the roots are restricted but large enough for them to be able to absorb sufficient moisture when watered. The roots will naturally wander over the top of the pot and this is natural.

Plastic pots are ideal, often they are clear see-through plastic to allow you to see the root system but this is really irrelevant. You can see from the top roots if they are in growth mode or not. Ensure the pot has several drainage holes in the base.

To make them look more attractive the pot can be placed in an attractive outer pot. Just ensure that when you water them they are not standing in water.

The best time to repot a Phalaenopsis orchid (not all orchids are the same) is immediately after it has finished flowering. Cut off the flower stem and then begin to re-pot as follows:

1. Choose a time when the compost is dry, just before you would normally water it is ideal.
2. Gently tease the plant out of the pot by turning it upside down and gently pulling it out by holding the central stem.
3. Shake off the old compost from the root system using you fingers. It should come away easily.
4. Look at the roots, if any are brown then cut them away to healthy growth near the base of the plant.
5. Trim half the roots to a length of 15cm / 6in using a sterilised sharp knife or scissors.
6. Place the plant in the new or existing pot to the same depth as in the original pot. Any surface roots should be left on the surface as they were previously.
7. Add the compost slowly into the pot around the roots. Tap the pot frequently to encourage the compost to settle into the pot. When halfway full, firm the compost down to start anchoring the plant. Fill with more compost to just below the top and firm down the compost gently a
8. gain.
9. Water the plant as normal (see here). Mist the leaves and any surface roots with water. If any leaves are brown and / or dying, remove them.

BUYING TIPS PHALAENOPSIS ORCHIDS

In their natural state Phalaenopsis orchids have no particular season for flowering and this is the same when they were raised by plant growers in artificial conditions. They can be grown to flower at any time of the year. Over time, in a normally heated house they will normally settle down into a rhythm of producing new flower shoots in September / October and flowering around March time.

It’s best to buy them when they have just begun to flower so that you see what the flowers look like. Choose ones with a few flowers on the stems plus a few buds. The leaves should be a glossy green and clean with little dust on them.

Garden centres have large displays of them for much of the year and are a good, if costly, place to buy them. Some of the larger supermarkets and diy stores also sell them at a discount. The other alternative is took for specialist orchid plant nurseries in your area.

As a generalisation it’s not sensible to buy orchids online because they do not transport well and postage costs are very high.

PROPAGATING PHALAENOPSIS ORCHIDS

Orchids can be grown from seed and from dividing existing orchids. Both methods are very difficult to achieve for the amateur gardener and can take anywhere from three to eight years before a flower is produced. It is not something we would recommend except for the hardened orchid enthusiast who wants to experiment/

PEST AND DISEASE PHALAENOPSIS ORCHIDS

Often Phalaenopsis orchids are grown for years without any signs of pests or diseases, these are relatively healthy house plants. Where trouble strikes it is likely to be caused by one the problems below. Use the comments / questions section at the end of this article if you want further advice.

LIMP LEAVES

The picture below shows a Phalaenopsis orchid with limp leaves. In this particular case they also have a shriveled appearance and are becoming brown in some areas. The saving grace for this orchid is that it also has a new, very healthy looking leaf shoot. Limp leaves are one of the commonest problems with orchids.

Your Phalaenopsis may have leaves which are limp but in a slightly better condition. The important thing to remember is that the limp leaves are caused by a problem which occurred a month or two earlier. Orchid leaves take some time before they begin to show signs of a problem.

The two most common causes are under-watering or over-watering. If you have under-watered the plant, it is simply suffering from a lack of water. Over-watering can have the same effect because it causes damage to the roots and they are then unable to absorb water and transfer it around the plant.

ACTION PLAN
This is the same for over and under watering.

1. If the plant has not been repotted over the last year, first repot it as described above. Remember that newly bought plants may well not have been re-potted for a year or more. re-potting will restore the correct level of moisture at the roots and also remove any compacted compost.
2. Using a sharp pair od scissors, trim off two or three of the worst affected leaves. Cut the leaves away near the main stem, it’s fine to leaves a stub of the leaf. If only part of the leaf is limp, cut away only the limp portion. Removing limp leaves (or parts of them) will reduce the risk of fungal and bacterial infections.
3. You need to leave at least two leaves on the plant to allow the plant to photosynthesise and grow new healthy leaves.
4. Re-read the watering instructions above and follow them carefully for the future. It is very likely that your orchid will recover however it may take a year for it to re-establish and produce new flowers.
5. Do not make the mistake of giving your orchid a “boost” feed. Stick to recommended feeding instructions above.

APHIDS ON ORCHIDS

Aphids are tiny green or brown insects which feed on the sap of orchids. New shoots are the most tender and often the first area which these pests attack. Often the aphids are visible on the plants but sometimes they are so tiny and camouflaged that you don’t see them. In this case the only sign may the white skins they shed.

They spread rapidly and are often introduced on new plants which are already affected. The best solution is to spray with an insecticide although non-chemical solutions are available. In our experience only the insecticides provide long term cure.

For more detailed advice on identifying and treating plants with aphids see the page here dedicated to this pest.

MEALYBUGS

These appear as white, slightly fluffy areas especially around the joint of leaves and stems, also around the growing area of new shoots. You may well also notice a sticky liquid over affected areas. This can attract black moulds.

If it isn’t all over the plant, treat specific areas by dipping a cotton bud in methylated spirits and wiping the fluff off and cleaning away any sticky liquid.

If the problem has spread then the chemical spray Bug Clear Ultra is your best option. Mealybugs have scales on their exterior and contact insecticides are only partially useful. Bug Clear Ultra however is a contact and systemic insecticide so much more likely to be effective.

BLACK SPOTS ON LEAVES

Almost always this is caused by a fungus, normally Pythium ultimum or Phytophthora cactorum. The fungus thrives in damp conditions. The affected leaves may also turn yellow.

Cut any affected leaves back to remove the areas affected by black spot. It’s fine to cut the ends of leaves off if only the end part is affected. The cut will quickly heal over. Then treat the plant exactly as for “limp leaves” as described here.