Repotting Orchids - A Primer Of Potting

Fir bark is the most common potting mix for nearly all epiphytic orchids. It is not only inexpensive but also available in various sizes and disintegrates gradually. The orchids absorb nutrients from the bark as it breaks down slowly, somewhat like a time-release fertilizer capsule let loose its nutrients over a period of time.

In fact, the finer the bark particles are, the quicker the nutrients are released. Since the bark particles also decompose, they have a propensity to pack together, thereby decreasing the air spaces in the potting mix and slowing the drainage process.

Fine quality of fir bark is generally used for small orchids having fine roots or seedling. In addition, they are used in combination with other materials to prepared mixes or growing terrestrial orchids like cymbidiums. The larger particles of fir bark are always used for potting mature orchids.

The large air spaces that exist between the bark pieces allows for excellent drainage of water. Nevertheless, as the bark decomposes very slowly, it provides very little nutrients to the plants. Therefore, it is important to feed the plants very often. If you do not use fir bark for potting, you may use coconut fiber chunks, which are rather similar.

However, coconut fiber is capable of retaining water for a longer period compared to fir bark. Moreover, unlike fir bark, coconut fiber is not used commonly for potting orchids. However, compared to fir bark, coconut fiber is available in plenty in the tropical regions, while people in other parts of the world may avail it through mail.

In some places, orchid growers use coconut fiber as a substitute of sphagnum peat moss, which is gradually more scar and, at the same time, a commodity that threatens the ecology.

Some of the commonly used materials for potting orchids include charcoal chunks, coconut-husk fiber, cork, fir bark, charcoal, lava rock, man-made mediums, osmunda, peat moss, perlite, rock culture, polystyrene foam, red wood bark, sand, tree fern fiber, soilless mixes and sphagnum moss.

Charcoal chunks

These are useful as they absorb surplus fertilizer and even contaminants. At the same time, charcoal chunks also help in improving movement of air inside the potting mix. However, charcoal chunks are rarely used alone.

Generally, they are added to other potting materials in a proportion of 1-to-10 or 2-to-10. Another plus point of using charcoal chunks is that they also help in maintaining a healthy growing medium.

Coconut-husk fiber

Coconut-husk fiber is actually a by-product obtained after processing coconuts. It is available in plenty compared to many other medium and when they are dry, they are fairly lightweight, making it easy to ship them.

Coconut-husk fiber has a light, reddish brown hue that contrasts well with the green color of orchids and makes the plants more attractive whether they are grown in clay or plastic pots.

This medium can be used independently for potting epiphytic orchids and it decomposes gradually releasing its nutrients slowly. Coconut-husk fiber works well with any balanced fertilizer for instance 23-19-17 or timed-release 14-14-14.


It is a partially deteriorating organic material and retains little water. When you use cork as potting material for orchids, you need to water the plants twice every week and repot the plants once in every three years. The cork mounts last for several years. Ideally, you need to use 20-20-20 fertilizers along with other trace elements.

It is worth mentioning here that cork is the most well accepted slab material used in orchid mounts. To prepare this medium, chunky, lightweight bark of the Mediterranean cork oak is boiled in water and used in the form of "nuggets" for potting orchids. However, cork is an inert substance and it does not provide the plants with any nutrient.

If you are using cork as the primary potting material, you must always add charcoal in the ratio of 60:40. Sometimes cork is also used in the form of an additive. While cork decays much slower than fir bark, it is prone to infestation of millipede, thereby turning it into slush very quickly.

Fir bark

This is an organic growing medium that deteriorates very fast. It is capable of holding water about 80% of its weight. If you are using fir bark for potting your orchid, you need to water it at least once a week and repot the plant once in a couple of years.

When you are using fir bark ensure that you use a 20-10-20 fertilizer whose pH level is 5. It is worth mentioning here that among all the potting material used for growing orchids, fir bark is the most common. Being a timber product obtained from the American evergreen firs, it is readily available too.

Generally, orchid growers prefer the deeply furrowed Douglas fir variety. The pieces of fir bark are sized differently - coarse, medium and fine qualities. The smaller the size of the medium, the more water it retains and also decays more rapidly. In order to get rid of resins, fir bark is first treated with steam and subsequently dried in kilns.

In fact, this process makes it difficult to wet fir bark in the beginning. So before using it for potting your orchid, you need to soak it in warm water for about 24 hours until they particles start floating. As you use fir bark in the pot, it starts decaying and after two years the potting mix turns into mush.

People who are just beginning to grow orchids often make mistakes while using fir bark. They wait for too long before repotting a plant grown in fir bark. Repotting the plants at the right time actually helps to avoid several problems. When you are using fir bark as potting medium, additives may prove to be helpful.

At the same time, it is advisable that you keep the potting mix open. A commonly used potting mix comprises fir bark, wool or redwood bark, perlite and peat in different ratios - for instance 7:1:1:1. Using expanded shale or stones may also be helpful in avoiding compacted decay.

Many growers erringly believe that it is necessary to use a fertilizer high in nitrogen content when you are growing orchids irrespective of which potting mix they are using. However, this is an erroneous perception. This is only for orchids grown in potting mix containing bark. This is because a common wood-rotting fungus decomposes bark.

This fungus also consumes plenty of nitrogen. Hence, orchids grown in pots with bark as a potting mix require a fertilizer with high nitrogen content. For instance, you may apply a nitrogen 20-10-10 fertilizer which will provide the fungus with additional nitrogen.

Although many have advocated using 30-10-10 fertilizer for orchids that are grown in bark, this fertilizer is also very high in nitrogen content and using a fertilizer in this ratio will encourage leaf growth, while the plants will bear fewer flowers. At the same time, the plant will be soft and grow very rapidly, which may invite pests. Therefore, you should ideally use 20-10-10 fertilizer.


Very often hardwood charcoal is added to redwood bark or cork, as they produce plenty of acid. However, the charcoal used for growing orchids is different from the pressed-powder briquettes that are used for barbecuing.

Moreover, charcoal is a common ingredient in commercially available potting mixes. Similar to lava, charcoal also collects salts. Therefore, you should not use it if you have hard water.

Lava rock

Both lava rock as well as gravel does not disintegrate ever, as a result they help in improving the air circulation around the roots. However, they cause drainage at a rapid pace and, hence, it is important that you water the plants at regular intervals.

In fact, lava rock and synthetic rock nodules are capable of retaining water better that gravels. However, these substances do not have any nutrient or food value. Therefore, if you are growing orchids in them, you will need to feed your plants more and frequently.

The advantage of using lava rock and gravels is that their weight keeps the container/ pot more stable and they are unlikely to fall or be blown over. Moreover, since these materials do not decay, you may sterilize them before reuse.

Man-made mediums

Man-made or artificial mediums include a range of products that are made from shale or clay and they have been treated with fire to take the shape of nuggets of any porous material, something comparable to a lava rock. In Hawaii, orchid growers widely use expanded clay along with a balanced fertilizer, for instance 20-20-20.


There was a time when people preferred using the knotted, matted roots of various species of ferns as a medium for growing epiphytic orchids. However, these days they are scarce and, at the same time, also expensive. Osmunda disintegrates very slowly and retains some amount of moisture.

At the same time, it allows free circulation of air. It also has some nutrient value for the plants. While many experts favour the use of this medium even today, people who are just beginning to grow orchids may find it difficult to deal with osmunda.

Peat moss

Compared to sphagnum, the water retaining capacity of peat moss is more, but this medium decomposes more quickly. There was a time when coarse peat was a preferred ingredient in potting mix for growing orchids.

Over the years, this medium has become scarce as well as expensive and hence it is seldom used by orchid growers now. There are some basic rules when using peat moss and these include - never mix this medium with tree fern, osmunda fiber, or cork.

However, you may blend peat moss with charcoal or fir bark. Coarse peat moss encloses some amount of nutrient and it also breaks down slowly, hence, when you are growing your orchid in this medium, you need to provide the plants a balanced fertilizer. You should avoid using horticultural peat since it is very fine and also dense for growing orchids.


It is also known as sponge rock. This medium is rarely used alone and often found in blended potting mixes. Perlite is lightweight and it is excellent for retaining water and promoting air circulation to the roots.

The water retention ability of vermiculite is too high and, hence, it also cannot be used alone. However, vermiculite is helpful in some potting mixes, especially those used for orchids that love moisture.

Polystyrene foam
(StryofoamTM, Packing Peanuts, Aerolite)

This is an organic material which is neither porous not does it deteriorates. Its pH level is neutral. Polystyrene form is basically a lightweight, white solid plastic that is very durable. It is composed of closed foam pores.

Occasionally, it is used as a substitute for perlite, particularly when it is crushed with the intent of aerating and opening up a potting mix. It is generally placed at the bottom of the pot with a view to promote drainage.

You may often mistake other foams for polystyrene - for instance, porous varieties like polyurethane and polyethylene that absorb salts which are damaging for the plants. A number of foams are treated chemically and they release toxins.

Then again, cornstarch is used for making packing peanut-shaped tiny binoculars and they are dissolved into disease-ridden, obstructive sludge when they are used for potting orchids.

Redwood bark
(Redwood Wool, Palco Wool)

This is again an organic material that deteriorates and holds about 50% its weight in water. The pH level of this material is 3.5. When you are using redwood bark as potting medium for your orchid, you need to water the plants once every week and repot them once in a couple of years.

It is advised that you use 20-10-10 or 20-20-20 fertilizer along with redwood bark. Redwood bark is heavily furrowed and this reddish fibrous bark is obtained from the sequoia tree in California. Different from fir, redwood bark does not enclose resin, its pH level is comparatively lower and it disintegrates more slowly.

When you are using redwood bark to pot orchids, it requires less nitrogen and, hence, adding 20-20-20 fertilizer is enough. Since redwood bark is quite expensive, it is mostly used in the form of an additive generally to fir bark.

In addition, this material is also available in the form of more absorptive fibrous "wool". In places where the heat as well as light is high, orchid growers use redwood bark as the principal ingredient in potting mix - especially, in Florida, where redwood bark performs better than fir. Usually, charcoal is added to redwood bark potting mix.

Rock culture

In situations where decaying or over watering are a problem, using inorganic rock culture for potting orchids may prove to be a more flourishing alternative to using bark. The three basic ingredients of rock culture comprise lava rock, stones and expanded shale pebbles.

When you add these to any decomposing potting mix, they help to promote air space within the medium. To attain best results, you may use plastic pots. The materials that comprise rock culture never decompose. Therefore, an orchid will require repotting when the plant has overgrown its pot.

However, when you are using rock culture, it means that the orchids should be grown virtually hydroponically. In addition, you need to provide the plants a complete and balanced fertilizer along with trace elements. In such a situation, the quality of water as well as the pH level is also vital.

(Builder's Sand, Sharp Sand)

This inorganic material does not deteriorate and it is capable of absorbing about 20% its weight in water and its pH level varies from neutral to 4.3. In fact, sharp sand is the silica or quartz part of soil that is present in gravel pits. However, it is not found in beaches.

The coarser (1/16 inch or more) the sand particles are, the better. Sand it an excellent terrestrial mix additive, especially for promoting aeration and drainage. It is worth mentioning here that sand is never used as the main ingredient in a potting mix.

Soilless mixes
(Premier Pro-Mix BX, Fisions Sunshine Mix #4, Metro-Mix, "Mud")

This material may be organic as well as inorganic and is semi-deteriorating. When using soilless mixes for potting your orchid, you need to water the plant twice every week and report the plant every year.

Moreover, you need to provide the orchids with a balanced fertilizer. Usually, the pH of soilless mixes is between 5.5 and 6.0 and it keeps changing over time. This potting mix is available commercially in various pre-packages and they comprise a blend of some vermiculite, sphagnum peat moss and at times even perlite.

The granular nutrients enclosed in soilless mixes include super phosphate, dolomitic limestone, potassium nitrate and calcium nitrate. It may be quite tricky to learn how to water this potting mix in the right way.

These potting mixes also decompose quickly and are, therefore, better when you use them for seedlings that love moisture and Phalaenopsis. The soilless mixes perform better for orchids in clay pots, especially those that require additional drying - for instance, Cattleya.

Sphagnum moss

Whether sphagnum moss is alive or dead, it is particularly for maintaining the surface moisture for the growth of delicate roots. This is the main reason why sphagnum moss is frequently used for wrapping the orchid roots that are mounted on bark slabs or on trees.

It seems that live (green) sphagnum moss contains some antibiotics and possesses fertilizing worth. Orchid growers have a preference for the Chilean or New Zealand sphagnum moss.

Here is a word of warning - using chlorinated or hard water will kill the live sphagnum moss. Therefore, it is advised that when using sphagnum moss as potting mix, you should always use rainwater or deionized water.

Tree fern fiber

This is a dark colored, porous and spongy material that is used in the form of "totem poles" to support philodendrons and other house plants similar to it. This growing medium is capable of retaining moisture and is well-aerated.

You may slice the tree fern fiber into slabs to pack them around the roots. Alternatively, you may also attach orchids to large pieces of tree fern fiber and subsequently their roots will either penetrate or cling to the tree fern fiber. In places where you find tree ferns in plenty, often the entire segment of the tree is hollowed out and utilized in the form of pots.


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