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Sphagnum moss

Also known as Long-fibre sphagnum, Orchid moss, Live sphagnum

Growing mediumDepends
Living sphagnum moss in a bog Photo: Agnes Monkelbaan · CC BY-SA 4.0

In short

Sphagnum moss is a bog moss sold dried as long strands (or grown live) for orchids, carnivorous plants, propagation and air layering. It holds huge amounts of water, so it is excellent for keeping roots moist but can easily cause rot if kept constantly wet.

How it looks

Live sphagnum forms soft, green to red cushions of small tufted stems with whorls of branches. Dried long-fibre sphagnum is pale tan to golden brown strands several centimetres long that become soft and spongy when soaked. It is different from peat moss, which is the decomposed material from deeper in the bog.

Signs

Moss that stays dark, compacted and slimy is breaking down and holding too much water; roots may become mushy. Dried-out moss turns crisp and is hard to rewet. Green growth on the surface is often live sphagnum regrowing, which many growers of carnivorous plants welcome.

What favours it

Special hyaline cells let the plants hold about 16–26 times their dry weight in water. Sphagnum acidifies its surroundings by taking up calcium and magnesium and releasing hydrogen ions.

Prevention

  • Wear gloves and long sleeves when handling sphagnum; the CDC notes the Sporothrix fungus that causes sporotrichosis lives on sphagnum moss and enters through cuts.
  • Pack moss loosely, not tightly; the AOS warns that tight packing markedly reduces aeration.
  • Keep it evenly moist, as it is hard to rewet once it dries completely.

Treatment

Start with the first step and move down only if the problem persists.

  1. Repot orchids out of old, compacted moss after flowering, trimming any rotted roots.
  2. Soak dried moss in water before use and squeeze out the excess.

Pros and cons

Pros

  • Holds a very large amount of water while staying airy when loosely packed.
  • Useful for propagation, air layering, rooting cuttings and reviving orchids with few roots.
  • Strongly acidic (the AOS gives pH 3.5); sphagnum bogs are natural habitat for many carnivorous plants.
  • The AOS rates it an excellent additive for helping a mix retain moisture without standing water.

Cons

  • Easily causes root rot if kept constantly wet, which is why many home growers do better in bark.
  • Hard to rewet once completely dry.
  • Harvesting affects wild bogs; New Zealand research found some sites need 11–32 years to fully recover, and Chile has regulated harvesting.
  • Can carry Sporothrix fungus that infects people through skin cuts.

Look-alikes

Peat moss
Peat is dark, fine and decomposed, dug from deeper layers of the bog; sphagnum moss is whole dried or living moss strands.
Coco coir fibre
Coir fibres are stiff, straight coconut husk strands, not soft branched moss stems.

Typical uses

Orchids (including Phalaenopsis in commercial production), Nepenthes and other carnivorous plants, propagation of aroids and other cuttings, air layering.

Sources

  1. Sphagnum — Wikipedia
  2. Beginner’s Series — Part 2: Media Mania Revisited — American Orchid Society
  3. Repotting Your Orchid — Clemson Home & Garden Information Center
  4. About Sporotrichosis — US Centers for Disease Control and Prevention
  5. What are the alternatives to using peat-based compost? — RHS

Written in our own words from these sources. Check a product label before using any treatment.