Gadenin日本語Get the appWhy crowding is deliberate
A cymbidium in a snug pot flowers. The same plant moved into a generous pot with plenty of fresh mix around it spends the next two seasons filling that space with roots and leaves and produces nothing. This is not a myth about orchids liking to suffer; it is that a plant with room to run puts its energy into rhizome and root, while a plant that has filled its pot has nowhere to put that energy except into fattening the growths it already has, and fat growths are what carry spikes.
So the default answer to whether a cymbidium needs repotting is no. Repot when there is a reason, not on a schedule. Most plants need it every two to three years, and a well-grown specimen in a large pot can go longer. Every repot costs you at least one flowering season, because cutting and disturbing roots in spring means the growths that summer are weaker than they would have been.
There are only three good reasons to do it: the mix has decomposed into a dark, soggy, fine material that no longer drains; the plant has pushed itself up over the rim so the new growths hang off the edge with nowhere to root; or the pot is so tight that it has cracked or you can no longer wet the root ball at all. Pretty much everything else can wait.
| Sign | What it means | Action |
|---|---|---|
| Bark still chunky, water runs straight through | Mix is intact | Leave it alone, however full the pot looks |
| Mix dark, fine and slow to drain, smells sour | Bark has decomposed | Repot into fresh coarse bark at the next chance |
| New growths hanging over the rim in mid air | Plant has walked out of the pot | Repot or divide after flowering |
| Pot bulging or split, roots lifting the plant | Severely root bound | Move up one pot size only |
| Water sits on the surface then runs off the side | Root ball is compacted or hydrophobic | Soak to rewet now, repot in spring |
| Plant flowered well, pot is crowded | Exactly what you want | Do nothing |
When to do it, and what to pot into
The window is right after flowering finishes, as the new growths are just starting to move in spring, and before they have made new roots. Roots that are already extending get broken by handling, and a growth that has begun to root and is then disturbed stalls for months. Aim for the point where you can see the new shoots at the base but they are still short.
The mix is coarse bark, and coarse means pieces roughly a quarter to half an inch (6 to 12 mm) across, larger than the medium grade sold for moth orchids because cymbidium roots are thick and want big air spaces. A good general mix is around three parts medium-to-coarse bark to one part coarse perlite or grit, with a handful of charcoal if you have it. Some growers add a little coir or fine bark for water retention, which suits a hot dry position but shortens the life of the mix.
Do not use ordinary potting mix, and do not use fine seedling bark. Both hold too much water around thick roots, break down within a year, and produce exactly the sour black sludge you were trying to escape. Plastic pots are preferred over terracotta because cymbidiums are usually root bound and a clay pot has to be broken to get the plant out.
Go up one size at most, to a pot that leaves about an inch and a half (4 cm) of space in front of the newest growth and almost none behind the oldest. Heavy pots or a slab under the pot help, because a big cymbidium in a plastic pot is top heavy and blows over.
Repotting step by step
Work somewhere you can make a mess and have a sterile blade, a pruning saw or an old bread knife, fresh bark, and the new pot ready before you start. Roots dry out fast once the plant is out of its pot.
- Get the plant out Squeeze a plastic pot all round to break the grip, then invert and pull the plant out by the base of the bulbs, not by the leaves. If it will not move, run a long knife around the inside wall or cut the pot away. Do not tug repeatedly; you will snap the rhizome.
- Wash the old mix off and look at the roots Tease the root ball apart with your fingers and rinse with a hose so you can actually see what you have. You cannot judge roots or find a place to divide through a solid block of old bark.
- Cut away every dead root Healthy roots are firm and white to cream inside. Dead ones are brown or gray and collapse to a hollow sleeve when squeezed. Cut them back to living tissue with a sterile blade. Shorten very long healthy roots to about six inches (15 cm) so they coil into the pot without kinking.
- Divide, or do not Only divide if the plant is genuinely too big or you want another plant. Cut the rhizome with a sterile saw into pieces carrying at least three or four pseudobulbs with a leading growth on each. Smaller divisions survive but take two or three years to flower again.
- Pot with the oldest bulbs against the rim Set the plant off center, with the back of the oldest pseudobulb almost touching one side and the growing front facing the open space. Hold it at the depth where the base of the bulbs sits just at the surface, not buried.
- Fill and firm hard Trickle bark in around the roots, tapping the pot on the bench and pushing the mix down with your fingers or a blunt stick until the plant is genuinely tight. A wobbling cymbidium makes no new roots, so firm it far more than feels polite.
- Stake it if it rocks, then water sparingly Tie the plant to a cane if it still moves. Water once to settle the mix, then keep it barely damp and out of strong sun for two to three weeks until new roots take hold, and hold off feeding for a month.
Backbulbs: the leafless bulbs behind the plant
Behind the leafy growths sits a row of older, leafless pseudobulbs called backbulbs. They are the plant's savings account. Three or four of them behind a division are worth keeping, because they carry the reserves that push a new growth through after repotting. Beyond that they take up space and can be removed.
Removed backbulbs will grow into new plants. Snap or cut them apart singly, dust the cut with cinnamon or leave it to dry for a day, then half bury each one in damp bark or perlite in a warm shaded place. A dormant eye at the base breaks within a couple of months and makes a shoot. It is a slow route, since a plant started this way takes three to four years to flower, but it costs nothing and it is how you replace a plant you have divided too hard.
Discard backbulbs that are soft, hollow, or blackened inside when cut. A shriveled but firm bulb is fine and will still shoot. A squashy one is rotten and will infect the bark it sits in.
Sterilize the blade between every plant, not just between sessions. Cymbidium mosaic virus spreads on sap through cutting tools and there is no cure. Flame the blade, or soak it in a fresh household bleach solution for a minute, before you touch the next plant.
After the repot, and what to record
Expect the plant to sulk. New growths often come up smaller in the first season after a repot, and a plant divided into small pieces may not flower for two or three years. That is normal and not a sign the job went wrong. Feed and water normally once new roots are running, put the plant outside for the summer as usual, and let it rebuild.
Label each pot with the date it was potted and the grade of bark used. Bark life varies enormously between mixes and climates, and after two cycles those labels tell you whether your mix lasts two years or four, which is precisely the information that stops you repotting on guesswork.
If you divided, note how many pseudobulbs went into each piece and where each division came from. When one piece flowers two years ahead of another, the size of the division is nearly always the reason, and having that written down settles the argument about how hard to split next time.