Gadenin日本語Get the appThe window is the new roots, not the calendar
Cattleya roots do their growing in one concentrated burst, usually just after a new growth begins to expand, and they will not restart on demand. A root that is cut or broken outside that burst simply stops, and the plant then has to wait until the next growth comes around before it can build a new root system. That is why a badly timed repot costs a full year, even though nothing looks wrong at the time.
So the trigger is visual. Look at the base of the newest pseudobulb or the new growth coming from it. When you see stubby root initials pushing out, green or white nubs a quarter to half an inch (5 to 12 mm) long that have not yet dived into the mix, you have a window of roughly two to four weeks. Root tips that are already six inches (15 cm) long and locked into the bark have passed the easy point, and breaking them costs the plant more than waiting does.
For most cattleyas that window falls just after flowering, as the next growth starts, and for many plants that is in spring. But plants vary and some flower on a different rhythm, so watch the plant rather than the season. If in doubt, wait. A cattleya will sit in old mix for an extra six months far more comfortably than it will recover from an untimely repot.
| What the plant is doing | Repot now? | Reason |
|---|---|---|
| New root initials just emerging at the base of the new growth | Yes, this is the window | Roots restart immediately into fresh mix |
| New growth swelling but no roots showing yet | Wait a few weeks | Roots follow the growth and will appear shortly |
| In bud or in flower | No | Buds blast and the flowers are lost |
| Bulb fully hardened, nothing moving | No | Cut roots will not regrow until the next cycle |
| Mix collapsed and sour, roots rotting | Yes, whatever the season | Rot costs more than bad timing |
How often it actually needs doing
Most cattleyas need repotting every two to three years, and the trigger is the mix rather than the plant. Bark breaks down into soft brown crumbs that hold water and exclude air, and once that has happened the roots start to die whatever you do about watering. Squeeze a piece of bark from the middle of the pot: if it is soft enough to crush between thumb and finger, the mix has gone and the plant needs it changed.
The other trigger is the rhizome. Cattleyas creep sideways, each new growth appearing a couple of inches in front of the last, so the plant marches steadily towards the edge of the pot. When the newest growth is at the rim and the next one will be over the side, it is time, regardless of how the bark looks.
Resist repotting for any other reason. Annual repotting on principle, common with houseplants, is actively harmful here. A cattleya in sound mix with room to run should be left alone, and a plant that has been left alone for two years usually flowers better than one handled every spring.
Doing it: pot size, mix and the steps
Work quickly and keep the plant out of the mix for as little time as possible. Have the new pot, the mix and a sterile blade laid out before you tip the plant out. Sterilize cutting tools between plants with a flame or fresh single-use blades, because several orchid viruses travel on sap and there is no cure for an infected plant.
Choose a pot that leaves about two inches (5 cm) of space in front of the newest growth and very little behind the oldest. That is roughly two years of forward march. Anything larger holds a mass of wet unrooted mix and rots the plant, and it is the most common mistake made at this stage.
- Free the plant from the old pot Squeeze a plastic pot or run a knife round the inside of a clay one to release roots stuck to the wall. Tip the plant out rather than pulling it by the leaves. If roots have cemented themselves to a clay pot, break the pot rather than tear the roots off it.
- Clear away the old mix Tease out every crumb of broken-down bark with your fingers or a blunt stick. Soaking the root ball in tepid water for a few minutes softens it and makes this far easier. Leftover decayed mix in the middle of the root ball will stay wet and start the same problem again.
- Cut out dead roots Trim off every root that is brown, hollow or papery, back to firm white tissue. Keep all the living white roots, even long ones, and coil them gently into the pot rather than shortening them. Dust large cuts with cinnamon or a horticultural fungicide if you have it.
- Divide only if you want to and the plant is large enough Cut the rhizome with a sterile blade so that each piece keeps at least three or four pseudobulbs with a leading growth. Smaller divisions survive but sulk for years before flowering again. If you do not want more plants, leave it whole; the plant does not need dividing.
- Position and pot up Set the oldest bulb against the back rim with the growing end facing the open space, and hold the rhizome level with the surface of the mix rather than buried. Trickle coarse bark in around the roots, tapping the pot to settle it, and firm it just enough that the plant does not move.
- Stake it so it cannot rock Clip a rhizome stake or a wire clip over the rhizome and into the mix. A plant that wobbles snaps its new root tips as fast as it makes them, and this single step is the difference between a plant that establishes in a month and one that takes a season.
Do not water for three to five days after repotting. Cut root ends need time to seal, and water on fresh wounds in a warm room invites rot. Keep the plant in slightly reduced light and steady humidity in that period, then resume normal watering once new root tips start moving into the mix.
Backbulbs and what to keep
The leafless old pseudobulbs behind the leading growth are still useful. They store water and starch and support the front of the plant, so leave three or four of them attached even though they will never make leaves again. Removing them to tidy the plant up weakens the growths that follow.
Bulbs beyond that, shriveled and hollow, can be cut away and discarded, or potted up separately in damp moss in a warm shaded spot. A firm backbulb with a dormant eye at its base will sometimes push a new growth within a few months and become a plant, though it is several years from flowering size. Treat that as an experiment rather than a plan.
Write down the date and the pot
Note the day you repotted, the pot size, the material and the mix grade, and mark the pot itself if you can. In two years those notes are the only reliable way to know whether the mix is due for replacement, because bark that is halfway through breaking down looks much the same as fresh bark on the surface.
Also record which end of the pot the leading growth faced when you put it in. When the growth reaches the rim two years later, the record tells you at a glance how much the plant advanced in a year, which is a better measure of how well it is being grown than the number of flowers on any single spike.