"Most orchid plants need to be repotted either when they outgrow the existing pot or when the potting media begins to break down, generally every two to three years," according to Kent Kobayashi of the Tropical Plant and Soil Sciences Department of the University of Hawaii. Successful repotting involves the correct potting mixture, removal of damaged roots, providing a sterile pot and drainage, and correct placement of the orchid in the new pot.
Potting Soil Mixture
Orchids do not thrive in typical potting soil, because their roots cannot dry out in soil. Air must be able to travel through the potting mixture to help dry the roots between watering days. Effective potting mixtures for orchids consist of any of these materials: a commercial orchid mix; sphagnum moss; redwood bark; fir bark; peat moss; tree fern fiber; coconut fiber; or Perlite. A combination of these can also be used for re-potting orchids.
When choosing the potting mixture, consider its moisture content. Smaller fibers or chips retain more water than larger chips. It is essential that the orchid roots are allowed to dry out between watering to prevent soggy roots.
Carefully remove the orchid from the pot after it has finished blooming. Clean off the roots under room temperature water. Inspect the roots, and remove any that are soggy or dried up and brown. Healthy roots are white and solid with green tipping. Trim off any orchid leaves that are yellow or brown.
Remove dried up flowers and soggy pseudobulbs. Pseudobulbs are enlarged parts of the stem where the leaves grow. They store water for when the orchid is in need of extra moisture.
Many orchid pots have side slits for proper drainage. If the pot has bottom drainage holes, make sure they are large enough for sufficient water drainage. Most orchid containers are constructed of clay or plastic.
Plastic pots often cause root rot in the orchid, because the plastic prevents the roots from drying completely. Clay containers allow the roots to dry out quickly, requiring the orchid to be watered more frequently.
Re-pot the orchid into a sterile new pot on a clean work surface. Use sterilized potting tools to prevent the transfer of diseases, insects and bacteria from old pots or pruning shears.
Place the orchid into the pot with the crown a little below the rim of the pot. Cover the crown with potting mixture to the same height on the plant as when it was previously planted. Press down firmly to set the orchid in the pot. Stake any parts of the orchid plant that are drooping.