Tips & Care: Basic Tools and Equipment for Orchids (Part 2: Potting Media)

Potting Media:

Fir Bark:  

Today, sterilized fir bark is probably the most commonly used orchid potting material.  Its ease of use and comparatively low cost make it an excellent choice for growing orchids of most genera.  Sterilized fir bark comes from several species of western US trees including white fir and Douglas fir.  It is cleaned and graded before being offered for sale as a potting medium.  Fine grades are suitable for seedlings, whereas coarser grades (pieces up to 1 1/2 inches) (2-3cms) may be used for large pots.  As with other materials, fir bark may be enhanced with additives, such as perlite, charcoal, aggregates, or redwood chips.  These are often sold as proprietary bagged mixes.

Potting orchids with fir bark is easier than potting in most other media; the relatively uniform pieces readily fall into place among the orchid roots.  Because fir barck may be resistant to water at first, many growers prefer to soak it before use.  This also serves to remove some of the dust generated in shipping, which will sink to the bottom.

Bacteria that feed on the bark and bring about its eventual decay use considerable availabe nitrogen, which may leave orchids nutritionally deficient. Therefore, it is necessary to use a high nitrogen fertilizer, such as 30-10-10 for orchids grown in fir bark.

In a controlled environment, fir bark may last two years in a pot.  It has a tendency to break down much quicker in warm subtropical conditions and therefore is not used in these areas as frequently as tree fern or aggregates.

Tree Fern: 

Also known by its Hawaiian name Hapuu, it is the fibrous trunk of various species of tropical tree ferns.  It is available as logs, slabs, or other solid shapes that may be used to mount orchids directly.  It is also available in shredded form in several grades of coarseness.  Chunks of tree fern may also be found at times and they are useful for larger pots and specimen plants.  Fine tree fern may be used alone or mixed with other ingredients for compost and seedlings.

Tree fern has excellent properties as an orchid potting medium; it is easy to use and provides good drainage and aeration to roots.  However, growers with tender hands may want to use gloves when potting with tree fern, because it can be abrasive.  It provides minimal nutrition to plants and lasts about two years under normal growing conditions.

Occasionally, tree fern is mixed with additives such as redwood bark, which is thought to discourage snow mold.  Coarse aggregates can also be mixed in to "stretch" the tree fern and improve drainage.  Orchids grown in tree fern are best fertilized with a balanced fertilizer, i.e. 20-20-20.

Aggregates:

The term aggregates refers to non-organic media such as lava rock and gravel. For the sake of convenience, we include expanded mineral products such as Aliflor and Solite as well as mined products such as Australian diatomite.  Like other potting media, these materials are available graded by size, with the smaller sizes being used for specimen plants and large pots.  The larger sizes are also useful as drainage for other potting media.  

Being inorganic, these materials do not break down and are ideally suited for warm climates and outdoor growing in rainy areas.  Heavier aggregates, in concert with clay pots, can provide the firm footing needed by top-heavy orchids in windy tropical areas.  Their quick drainage also allows orchids to withstand considerable rain during wet summer months.

Aggregates are easy to use; the uniform pieces readily fall into place among the orchid roots.  Keep in mind that large pots tend to get heavy, especially if the pot is clay.  Although Solite is reported to hold up to 30% of its weight in water, these materials generally require more frequent watering than organic media.  As with other media, additives such as sphagnum may be used to modify the moisture holding properties.  Aggregates provide excellent drainage and aeration to orchid root systems and will last indefinitely. Although they can be reused, this is not advisable unless the used media can be sterilized.

Complete nutrition must be supplied when potting with aggregates;  use a balanced fertilizer such as 20-20-20. It is also recommended to thoroughly flush potted orchids with clean water monthly to avoid fertilizer salts from building up.  Many growers like to prerinse their medium prior to use to remove dust and fine debris.

Sphagnum moss:

This has become increasingly popular as an orchid potting medium in recent years, particularly with the introduction of high-quality, long fibered New Zealand sphagnum.  Comparable quality is also available from select Chilean sources.  There are different grades of sphagnum available from locations throughout the world;  choose the one that fits your budget and quality requirements.

Sphagnum is easy to pot with; however, you should presoak it overnight in a bucket of warm water.  Many growers like to add a teaspoon of an algicide such as Physan or RD-20.  Squeeze it out gently before packing it around the roots, taking care to not pack too tightly.  A rhizome clip or stake may be used to stabilize the orchid.

Sphagnum moss is difficult to rewet once it has dried out so it is best to keep the plants evenly moist but not soaking!!!  Adjust your watering schedule accordingly.  As a result, this medium is not for orchids that like to dry thoroughly between waterings.

Although it is thought that the moss supplies some minor nutrition, it is best to fertilize plants potted in sphagnum with a balanced fertilizer such as 20-20-20.  Additives such as charcoal and perlite are often used to prevent the moss from compacting and keep the mix open.  Sphagnum can last up to two years but in practice, plants are usually repotted yearly, especially phals.

The moss can harbor the fungus that causes the lymph infection Sporotrichosis.  Although cases of infection are not especially common among orchid growers, the fungus can enter the body though a cut or other opening and cause symptoms from mild to severe.  As a precaution, wear rubber gloves when working with sphagnum moss.

Osmunda:

Until the early 1950's, osmuda was the potting media used for growing orchids.  Its increasing scarcity and consequently high price has caused it to fall out of favor.  It also requires some skill to be able to successfully pot with osmunda.  Other potting materials available today are much easier to use.  There are certain instances when this medium might be just what is called for to coax a recalcitrant orchid into growth. It is also useful to put a small pad of osmunda beneath the rhizone when attaching a plant to a mount; this provides a little extra moisture while the plant gets established.

The fibrous roots of the osmunda fern provide a higher quantity of nutrients than most other potting materials, therefore they require more dilute fertilizer application.  Use one-half the strength used for other media.  Despite the fine texture of osmunda, it does not break down quickly and will generally last in excess of two years.  Additives such as charcoal can be used to maintain the openness of the mix and keep it from souring.

Potting with osmunda requires some practice; chunks are torn into appropriately sized pieces and forced into the pot and around the roots with a "potting stick" or similar tool (you can use a sushi chopstick), creating enough pressure against the roots to hold the orchid firmly firmly in place.  An orchid that has been properly potted in osmunda usually requires no clips or stakes unless it is top-heavy by nature.

Coconut husk chips (CHC):

Graded chips, or chunks of coconut husk have enjoyed some popularity as an orchid growing medium.  Indications are that it may offer better aeration and stay less wet than coconut fiber.  Some growers have had success using the fine grade on its own as a seedling medium.  It seems to provide a constant, even source of moisture without the dry to wet problems of sphagnum, yet does not stay soggy.  It is common practice with this medium to provide an overnight soaking prior to rinsing with water to leach out any accumulated salts that may be present on the coconut husk, depending on its source.  The chunks may be used on their own or mixed with charcoal, Aliflor or lava rock.

There are also many formulated potting mixes available at garden supply  stores that are suitable for growing a wide range of orchids.  We have not included those here because we do not endorse any particular proprietary potting mix and the types and availability vary regionally.

Thanks Ned Nash