Orchids do not grow in soil. Soil does not allow enough air to flow around orchid roots. There are many materials which can anchor orchid roots while still permitting air to move around them. Ground tree bark and moss are two of the most common. They are often combined with perlite, vermiculite, or charcoal to keep the mix open and permit air flow. Do not use barbecue charcoal since it contains chemicals that will kill the plant.
- Most orchids are air plants -- In the wild orchids are epiphytes, or air plants, growing with their roots exposed to the elements. In a pot with moss or bark, orchid roots don't enjoy the same air movement. When the potting media starts to decompose, even less air can move through it. Some plants, like Paphiopedilums, are sensitive to decomposing potting media and need to be repotted annually. Others, like Cymbidiums, dislike repotting and do not need to be repotted often.
- Repot after plants finish blooming -- This is when they begin a cycle of leaf and root growth, and it is the ideal time to repot.
- Use plastic, ceramic, or clay pots -- Only use clean pots with drainage holes in the bottom. Clay pots are porous, which means that water and air can pass through the sides. While the roots will enjoy the added circulation, they will also dry out faster, especially on hot summer days. Over time, clay pots may also become discolored and unattractive. Plastic and ceramic pots will retain moisture much better, but do not allow as much air circulation around the roots. Plastic pots weigh less and are more likely to tip over when an orchid is top-heavy with flowers.
- Select the correct pot size - Most orchids prefer to be somewhat cramped in small pots. Pots that are 8 inches/20 cm or larger may remain very damp in the center, causing the potting media to decompose quickly and blocking essential airflow to the plant's roots.
Steps for Repotting Orchids
- Wash your hands with soap and water first.
- Remove the orchid from its pot and clean off the potting media - Water the plant to soften the roots. Give the pot a firm bang against a solid surface. Gently pull out the plant, and remove as much of the potting media from the roots as possible. Rinse away any remaining bark or moss.
- Inspect the plant -- After you remove the plant from its pot, examine the roots. How deeply did they grow into the pot? Are they fine roots or thick roots? Are they firm and healthy, with new, light-green growth? Or are they brown and squishy, which means they are dead and should be removed?
- Remove dead roots and leaves - After washing off the roots, it should be easier to see which roots are firm and alive, and which have become soft and squishy. Remove any dead roots by gently pulling at them, or cutting them off with a sterile knife or scissors. You may feel like you are harming the orchid, but if you leave the dead roots attached, they will rot and possibly spread disease to the rest of the plant. In their natural habitats, dead roots would typically be worn away by wind and rain. While there are some orchids with delicate roots which must be treated carefully, most can handle a thorough cleaning. After removing the dead material, rinse the entire plant again.
- Pick an appropriate size pot -- Always use a clean pot. If the orchid roots fill the pot, use a new pot that is 1 inch/2.5 cm wider. If the roots have not grown deeply into the old pot, use a smaller pot. Extra bark in the bottom of a large pot will rot quickly, and can choke off oxygen flow. If the pot is too deep, fill the bottom with a layer of clean rocks, marbles, or styrofoam peanuts. These help ensure good drainage and air movement.
- Choose the new potting material -- Never reuse old potting material. Premixed potting media can be found at many stores. You can also make your own by combining shredded bark, moss, charcoal, perlite, or vermiculite. For thick roots, use coarser bark, and for fine roots, use small bark. Use plant or aquarium charcoal, not barbecue charcoal.
- Think about good drainage -- Orchids require excellent drainage to prevent water from standing around the roots and causing rot. Make sure pots have drainage holes at the bottom. Many orchids are top-heavy, especially when they are blooming. Placing rocks in the bottom of pots helps prevent them from tipping over, and can also help improve drainage (make sure the rocks do not block the drainage holes!)
- Position the orchid in the pot -- If the plant's new growth comes from one central stem, place the plant in the center of the pot. If the plant's new growth comes out sideways from the older growth, place the old growth against the sides of the pot so that the new growth has room to expand out.
- Place the plant in the pot - Do this before you add the potting media.
- Fill in the potting media around the roots - Pour it around the roots. Tap gently on the pot to help the media settle. Keep adding more until the media is 1 inch/2.5 cm below the top of the pot. Check that the plant is stable and positioned well. Gently tying the plant to a stake can help to anchor it.
- Keep the newly repotted plant in the shade - Give it 2-3 weeks recovery time, and then slowly move it back up to its normal light level. Water regularly.