Why do old Phalaenopsis (moth orchid) plants need repotting, and can they survive without it?

Anyone who grows Phalaenopsis knows that after a year or two the plant becomes an old specimen, the leaves are no longer so perky, and it blooms less. At this point some people say"it's time to repot," while others think "leave it alone, what if moving it kills it?" So why do old plants really need repotting? Can they truly not survive without it?

Why do old plants have to move house? The roots of a Phalaenopsis have grown in the pot for a year or two, and long ago have tangled the sphagnum moss or potting medium into a dense mass; the roots have no room to spread out, so their ability to absorb nutrients declines.

Then there is the problem of the potting medium aging. Sphagnum moss rots after long use, turning into a sticky clump that holds water but does not let air through; bark medium breaks down into dregs over time, clogging the pot so it feels stuffy. At this point the roots either rot from being smothered or cannot take up water, and old plants are weak to begin with, so after such an ordeal they easily get yellow leaves and root rot, let alone bloom.

There is also a hidden reason: some old plants sprout small side shoots at the base, that is, small plantlets, and these plantlets crowd into one pot competing for nutrients, until in the end the old plant grows weaker and weaker and the plantlets cannot grow large either. Separating them when repotting lets the old plant catch its breath and lets the plantlets become independent plants, killing two birds with one stone.

So someone asks: my old plant still looks alright, can it survive without repotting? In fact it can survive in the short term, but its condition certainly will not be good.Someold Phalaenopsis plants have not been touched for three years, the leaves dropped from6 to3, last year they barely opened two flowers, this year there is simply no movement, and half the leaves have turned yellow, so getting them to bloom again is even harder.

But repotting also depends on timing; it cannot be done just anytime. It is best to choose spring or autumn, when the temperature is15-25°C, because then old plants have a strong ability to recover. Summer is too hot and easily causes root rot, winter is too cold and will cause cold damage, so by no means mess around with it.

When repotting, remember to strip off all the aged medium, cut away rotten roots and hollow roots, dab the wounds with carbendazim and let them dry for half a day. Do not make the new medium too wet: squeeze the sphagnum moss until it no longer drips, or soak the bark through and let it drain. When potting, do not bury it too deep; let part of the roots stay exposed to breathe, which is a little habit of Phalaenopsis.

Put plainly, repotting an old plant is like moving an elderly person into a roomier house: clear out the useless clutter, swap in some new furniture, and once they are comfortable they naturally perk up. If you really cannot be bothered, then at least scrape off some of the old surface medium each year, add a little new, loosen the medium and let air in; that is still better than leaving it stuffy all the time.