Dendrobiums orchids range from tiny to very large (sometimes, overhanging) stems. Whatever the size, dendrobiums are considered as delicate orchids, needing extra care. These orchids can be evergreen as well as deciduous. Repotting dendrobiums can be tricky; frequency of repotting depends upon the species and requirement of the time.

How to know when to repot the dendrobe
. Dendrobiums mostly grow in tight bunches, with new growth (keikis) emerging close to the old stems. They can peacefully grow even in a small pot, but if the orchid seems to have outgrown the pot and there is no space left for new growth to emerge, then it is time to repot.
. Repotting should be done after flowering is over and the next growing season is about to start.

When not to repot
. Dendrobiums detest being disturbed. Infact, the orchid may fail to recover if frequently repotted.
. Deciduous type of dendrobiums need only be repotted when the growth medium had degraded and needs to be changed. In these orchids the previous year's leaves and stems die off and new shoots emerge from the base or internodes of the shrivelled stems (aka pseudostems).

How to repot
. Place all the materials required in one place. You will be requiring new containers like pots/baskets etc., growth medium, tools and separate the plant material.
. Select a clean place like a table top where you have sufficient space to work.
. Using clean the tools prevents spread of viral and bacterial infections, which are easily spread through dirty tools. Before using all trimming tools, clean with soap and water then wipe with alcohol.
. Select the size of the container in which you want to place your orchid. Dendrobiums do not require big containers; however it should have sufficient area for the orchid to grow undisturbed for at least three years. Miniature dendrobiums can also be grown in shallow trays/mounts. The container should have an adequate drainage outlet so that there is no water stagnation inside the container when you water the orchid. I grew my dendrobiums on foot long branch pieces. These are easier to manage those dendrobiums which have long stems.
. Choose the growth medium wisely. Do not reuse the old medium, to avoid spread of disease and remember orchids also derive some nutrition from the degrading growth medium. Most dendrobes are epiphytes, so the growth medium should be able to dry quickly after watering. You can use orchid specific commercial growth medium. Other options are coconut chunks, moss, bark pieces etc.
. Now to repot the dendrobium. Remove the orchid from the container and discard old growing medium. If growing in a pot, hold the base of the orchid firmly remove it from the old pot (slightly tap the pot if the orchid is struck). Place it on a clean paper. Clean the clean and check for any rotting or disease parts. Remove the diseased, rotten or dead parts with clean cutting tools. If the orchid has grown in volume and one container cannot take all the stems (or pseudostems), then separate the stems in such a way that each group (of stems) carries new growth or at least healthy stems.
. If you planning to repot your dendrobium in a pot, then prepare it by adding some of the growth material at the base. Place the orchid inside the container in such a way that any new growth has good amount of area to grow into. Cover the base with rest of the medium. The newly potted dendrobe does not like to be disturbed or shaken, so you can tie the dendrobium stem to a stalk placed in the middle of the pot. If you are mounting your orchid, then tie some of the growth medium (like coconut husk or chunks) before tying the orchid to it.
. Do not cover the aerial roots (air roots).
. Water it sparingly and place it in warm shaded place for a week or so, to let it get accustomed to the new setup. Shift it only when your see new growth emerging.

Notes:
. You can also use stems to generate new plantlets by removing the leaves from healthy stems and place them horizontally on the growth medium. Keep watering to minimum. Young plants or keikis will grow from the internodes of the stem in about forty to fifty days.
. It is advisable to label your orchid. It will help in identifying the needs particular to that orchid.