Why do old Phalaenopsis orchids need repotting to survive?

Those of you who grow Phalaenopsis orchids have surely run into this question: your old plant at home has been growing for a year or two, looks fine on the whole, so does it still need repotting? Is it really true that it won't survive without repotting?

Why do old Phalaenopsis orchids need repotting? The first reason is that the potting medium has "worn out." As we all know, Phalaenopsis orchids generally use bark, sphagnum moss and the like as potting medium. Over time, this medium becomes like an old worn-out rag: the bark crumbles into bits, the sphagnum moss rots into mud, and it completely loses its air permeability and drainage. After watering, the medium becomes stuffy and wet inside, and the orchid's roots simply can't breathe; over time, problems like root rot and black rot all come knocking.

The second reason is that the roots have "nowhere left to live." Phalaenopsis orchid roots grow especially fast; in an old plant grown for two or three years, the roots may have already packed the pot completely full, and may even poke out through the drainage holes in the bottom and the ventilation holes in the sides just to get some air. With no new space for the roots to grow and nutrients unable to keep up, the plant naturally gets worse and worse.

There is another easily overlooked reason -- nutrients are used up. Although you fertilize as usual, after a long period of absorption the nutrients in the potting medium have long been eaten clean by the orchid. Even if you fertilize, the effect is greatly reduced; repotting with fresh medium is like moving the orchid into a new home, and preparing a table full of rich food for it too.

So can an old Phalaenopsis orchid not survive without repotting? Actually, it's not absolute. If your old orchid is in especially good shape, with glossy leaves and normal blooming, and the potting medium hasn't completely compacted or rotted, then it can keep living for a while without repotting. But this is only lingering on; over time the problems will definitely show up: fewer and fewer flowers, and leaves that go soft and floppy.

For an old plant, repotting is like giving it a "health treatment" that lets it regain its vitality. But repotting also requires the right timing and method. It's best to choose spring or autumn after the flowering period ends, and to repot when the temperature is 18 - 25°C; at this time the orchid has strong recovery ability and is unlikely to run into problems. When repotting, don't yank the roots by force; gently clean off the old medium, trim away the blackened and rotted roots, then soak them in a carbendazim solution to disinfect them, and finally plant them into fresh medium.

Repotting an old Phalaenopsis orchid is not a "mandatory death order," but for it to stay healthy and bloom year after year, repotting is absolutely a wise choice! Don't be lazy -- hurry up and check whether your old plant needs repotting, and get to work on it.