Orchids should not be replanted without compelling reasons. However, the measure is necessary, if the plant material decomposes too much and is therefore impermeable to air. When in doubt, be aware of it, that it must remain in good shape for another year, if one does not decide to transplant. Similar considerations apply to growth. The new shoot to be expected should definitely still find space in the vessel and not grow beyond its edge. Neglected plants, whose shoots protrude freely into the air and have formed many aerial roots, are usually difficult to fix again.
There are some rules for the frequency and timing of transplanting, have general validity. However, they are modified individually depending on the opinion and experience of the respective carer, without damaging the plants, if it is done sensibly.
Should be transplanted annually: Calanthe, Dendrobium phalaenopsis and its hybrids, Paphiopedilum, Phaaenopsis u.a.
Every two years: Cattleya, Dendrobium Oncidium, Odontoglossum u.a.
Every three years: Cymbidium, Vanda u.a..