Question: The leaves of my orchid are turning yellow and falling off. Is it dying?
Answer: Not necessarily. It’s normal for an orchid to lose its old leaves, especially after it moves froma commercial greenhouse with very humid air to the extremely dry air of the average home in winter. Also, as new leaves appear in spring, the plant often loses a corresponding number of old leaves.
You also have to take into consideration the type of orchid. Sympodial orchids, like cattleyas, oncidiums and miltonias, produce swollen stems called pseudobulbs and each one flowers only once, although the pseudobulbs can remain green for years. They will eventually lose their leaves once they have bloomed and there is nothing wrong when that happens.
Some dendrobiums react even more dramatically. Their pseudobulbs take the take the form of a thick cane with leaves on alternate sides. After a cane blooms, all the leaves of some deciduous dendrobiums drop off one after the other… and that too is normal!
Let’s assume though that your orchid is a phalaenopsis (Phalaenopsis), also called a moth orchid, simply because it is by far the most widely sold orchid. If so, here are some other causes that might explain the yellowing of its leaves.
- Lack of light over a long period of time can cause the lower leaves to turn yellow. So move the plant closer to a bright window. Ideally it would need bright light with a few hours of morning sun much of the year. In upper latitudes, full sun in winter is not too much.
- Too much sunlight can cause the leaves to turn yellow, but this time it will be the upper leaves or those closest to the window that are effected. If this happens, move the plant to a spot less intensely lit or draw a sheer curtain between it and full sun. This is not likely to be a problem for phalaenopsis grown indoors in northern regions, where sunlight indoors is never very intense, but can occur on plants that spend their summer outdoors.
- Excessively cool temperatures, only likely to be a problem in winter, may also cause leaf yellowing. Phalaenopsis are tropical orchids and don’t appreciate temperatures that fall regularly below 60˚ (15°C). In fact, they’ll be happier at around 70˚F (21˚C) year round except for a short period of cool nights in the fall to help stimulate bloom.
- Dry air, a major problem in homes during the winter months, can also be a factor. You really should grow orchids on a humidity tray (pebble tray) at that season.
An insect infestation, especially of mealybugs or scale insects, can cause overall weak growth accompanied by the yellowing of lower leaves. If you see small brown “shields” on the leaves or the flower stalk, the problem is scale insects, whereas white cottony growths, especially in leaf axils, are actually mealybugs. Both exude honeydew, a clear sticky liquid that falls on the lower leaves and nearby furniture. Both insects can be controlled with insecticidal soap or rubbing alcohol. And put your infested plant in isolation, away from any other plant.
- A chronic lack of water may result in limp, dangling leaves and eventually to yellowing of the lower leaves. Learn how to properly water your orchid, applying water gradually over the substrate until surplus water drains out of the plant into an ample saucer below. (Beware of overly small saucers: you then tend to underwater in order to avoid their overflowing and thus fail to adequately water your orchid. Saucers should be at least 1 inch/2,5 cm) wider than the bottom of the pot).
If you have difficulty watering an orchid, try soaking the whole root ball, pot and all, in the sink or a pail of tepid water for 10 to 15 minutes to make sure the roots have really gotten the moisture they need, then letting the excess water drain away before you put the plant back in its place.
- Root rot, curiously, has the same symptoms as lack of water: the leaves become limp and droopy. It’s caused by overwatering, by never draining the cache-pot after you water by watering with ice cubes or by degraded growing mix that holds too much water. If so, in addition to the limp, yellowing leaves, you’ll see that most of the plant’s roots are brown and either dried up or rotting rather than being thick and silvery gray with a green tip like healthy phalaenopsis roots. To be sure, sniff the growing mix: it if has a rotten potato smell, some roots are certainly rotting. If so – and if the plant still has several healthy roots – you may still be able to save it. Unpot the plant, cut off the rotten and dead roots and repot in a fresh orchid growing mix. That said, root rot is often fatal and indeed kills more phalaenopsis than any other cause.
You should by now have some idea as to why your orchid has yellowing leaves. Try to correct the problem you think is most the likely culprit and, with a bit of luck, your orchid will soon start growing and blooming again!