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Repotting and potting media for orchids

Maxillaria huebschii
Photo: Jardin botanique de Montréal (Gilles Murray)
Maxillaria huebschii

There may be several reasons for repotting an orchid. Generally speaking, these plants should be repotted every 2 or 3 years or if:

  • the potting medium has decomposed
  • the plant has outgrown its pot
  • the medium does not have enough drainage
  • there is a problem with root rot

Most orchids can be grown in containers in a variety of potting media. The materials chosen should be light and well aerated, retain moisture well and offer good root support. The organic components should decompose slowly. The container must have drainage holes. Clay marbles or styrofoam “peanuts” may be placed in the bottom of the pot to improve drainage.

Some orchids are grown as epiphytes, attached to plaques made from cork, tree fern fibre or synthetic materials (Bulbophyllum sp.). Vandas are usually planted in slatted baskets, in coarse pieces of bark.

Finally, a number of orchid species do well when grown semi-hydroponically in inert potting material (expanded clay marbles) with natural fertilizer.

You may choose a single material (fern fibre or coconut bark) or combine different materials: redwood, Douglas fir or coconut bark, tree fern fibre, cubes of rock wool, perlite, diatomite, volcanic rock and charcoal. Sphagnum moss is not essential. It can be replaced with rock wool or diatomite (diatomaceous earth). These materials are very porous and retain water well, in addition to being well aerated. They also cut down on watering and repotting because they do not decompose.

Choose the particle size (fine, medium or coarse) according to the size of the roots and the plant’s stage of growth. Finely crushed, water-retentive materials are suitable for plantlets and orchids with fine roots (Miltonia sp.). Medium-textured materials are used for most medium-sized plants. Coarser materials ensure better drainage for mature orchids in large pots.

Recommended proportions and sizes of potting media materials
  Fine (2-7 mm) Medium (7-15 mm) Coarse (15-25 mm)
Tree or coconut bark 1 1 1
Rock wool; diatomite; fern fibre 1 1/2 1 1/2
Perlite 1/2 1/2 1/2
Charcoal 1/4 1/4 1/4

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