Gadenin日本語Get the appCrown rot: the one that kills in a week
The crown is the tight cup at the center of the plant where the leaves meet the stem, and it contains the single growing point from which every future leaf will come. Water that sits there overnight, especially in a cool room with still air, lets bacterial soft rot in. Once the growing point is destroyed, the plant cannot make another leaf, and a moth orchid that cannot make leaves is finished no matter how good its roots are.
The first sign is a leaf that turns a translucent, water-soaked yellow-brown at its very base, right where it joins the stem. Press it gently and it feels soft and slimy rather than firm, and it will pull away from the plant with almost no resistance, often with a distinctly bad smell. This can go from nothing to a lost plant in three or four days, which is why it is worth glancing into the crown every time you water.
Act the moment you see it. Take the plant somewhere dry and warm, cut away every soft, discolored, wet-looking piece of tissue with a sterile blade until the cut surface is firm and clean, and blot the whole crown dry. Keep it dry, in good air movement, for a week, watering only the bark and only from the side. If the growing point survived, a new leaf will appear. If it did not, keep the plant anyway for a few months: some will throw a basal keiki from the stem below the damage.
Prevention is entirely about technique. Water in the morning, pour at the edge of the pot rather than into the middle, tilt and blot the crown after watering or after any shower or misting, and give the plant enough air movement that a splash dries within an hour.
Root loss: the slow version of the same problem
Root rot kills far more moth orchids than crown rot, but it does it invisibly over months, so the owner blames something else. A root that has been kept wet with no air dies, turns brown and hollow, and squashes flat and papery between finger and thumb. A healthy one is firm and plump, and white, silver or green depending on how much water it holds.
The confusing part is that the symptom above the pot looks like drought. Leaves go soft, wrinkled and leathery and droop over the rim, exactly as they do when a plant is bone dry, because in both cases the plant is short of water. The owner waters more, kills more roots, and the leaves go limper. If your plant has limp leaves and the bark is wet, the problem is drowning, and more water will finish it.
Check by lifting the plant out of its pot. If most of the roots are brown and hollow, repot immediately into fresh coarse bark, cut every dead root away, and use a pot small enough that the surviving roots fill it. Then water sparingly, letting the medium go properly dry between soakings, and support the leaves with humidity while new roots grow. A plant with even three or four live roots will usually recover over a season.
The commonest single cause is a decorative cover pot with no drainage hole, quietly holding an inch (2.5 cm) of water in the bottom that the owner never sees. Look inside yours before you look anywhere else.
Mealybugs, scale and the pests that hide
Mealybugs are the classic moth orchid pest: small, soft, oval insects covered in white waxy fluff, clustered where the leaves overlap the stem, in the crown, under the papery bracts on old flower spikes, and among the roots at the surface of the bark. They suck sap, deform new growth, drop sticky honeydew that goes on to grow black sooty mold, and they can transmit virus between plants.
Scale insects look completely different: flat or domed brown or tan discs, three-sixteenths of an inch (4 mm) or less, stuck fast to the undersides of leaves along the midrib and to the flower spike. They do not move and are easily mistaken for a blemish on the leaf. Scrape one gently with a fingernail: if it lifts off and leaves a damp mark, it is scale.
For a light infestation of either, treat by hand. Dip a cotton bud in rubbing alcohol and touch every insect you can find, which kills them on contact by dissolving the waxy coat. Go over the whole plant, including the undersides of every leaf, the crown, the spike, the bracts and the top of the bark, and repeat every five to seven days for at least three rounds, because eggs hatch after you treat. Isolate the plant from your others while you do it.
For a heavy infestation, wash the plant thoroughly and use a horticultural soap or oil spray, testing on one leaf first and keeping the plant out of direct sun while it dries. Do not spray open flowers, which mark easily.
Bud blast: buds that yellow and drop before opening
A spike full of fat buds that turn yellow, shrivel and fall without opening is called bud blast, and it is not a disease. It is the plant reacting to a sudden change in its conditions while the buds are at their most sensitive, and it usually happens within a week or two of something in the environment changing.
The usual culprits are a sharp drop or rise in temperature, a cold draft from an opened door or window, the hot dry air of a radiator or heating vent, letting the plant dry out completely at the wrong moment, moving the plant to a much darker spot, or ripening fruit in the same room. Fruit gives off ethylene, and moth orchid buds are markedly sensitive to it; a bowl of apples or bananas next to a spike in bud will cost you the flowers.
There is no cure once the buds have gone; they will not be replaced on that spike. The response is to settle the plant in the position where you want it to flower before the buds swell, and then to leave it strictly alone until the flowers are open and set. Keep it away from doors, heat sources and the fruit bowl, and keep watering steady rather than letting it swing between soaked and bone dry.
A moth orchid that drops the lowest one or two buds on a long spike while opening the rest is not blasting. That is normal, and it usually means the plant simply set more buds than it had energy to open.
Reading the leaves: a quick diagnostic table
Most complaints about a moth orchid come down to one of a small number of causes, and the leaves are where you read them. Use the table as a first pass, then check the roots to confirm, because so many symptoms above the pot are caused by what is happening below it.
| Symptom | Most likely cause | What to do |
|---|---|---|
| Limp wrinkled leaves, bark wet | Roots rotted from overwatering | Repot into fresh coarse bark, cut dead roots, water less |
| Limp wrinkled leaves, bark bone dry | Genuinely underwatered | Soak thoroughly and shorten the interval |
| Lowest leaf yellowing slowly and evenly | Natural ageing of an old leaf | Nothing. Let it drop on its own |
| Leaf soft and brown at the base, bad smell | Crown or stem rot | Cut back to clean tissue, keep dry, improve airflow |
| Dry bleached papery patch on a leaf | Sunburn from direct sun | Move back from the glass or add a sheer curtain |
| Black or brown spots with a yellow halo | Fungal or bacterial leaf spot in still damp air | Cut out the spot, keep leaves dry, add air movement |
| Sticky leaves, black sooty film | Honeydew from mealybugs or scale | Find and treat the insects, then wash the leaves |
| Dark green floppy leaves, no flowers for years | Not enough light, and no cool night trigger | Move nearer a window, give cool autumn nights |
What to write down
Record the date you first see any problem, not the date you finally act on it. The gap between the two is usually where a plant is lost, and seeing it written down changes how quickly you respond next time.
For pests, note the date of every treatment. Mealybugs need three or four rounds a week apart to break the hatching cycle, and it is remarkably easy to do two, decide the problem is gone, and find a full colony a month later. A written treatment log is the difference between clearing an infestation and living with it permanently.
For rots and bud blast, note what changed in the fortnight before: a move, a cold night, a missed watering, the heating going on for the season. The cause is nearly always in that window, and after a couple of years your own notes will tell you which of your positions and habits are the risky ones.