How to water a Phalaenopsis orchid

To water a Phalaenopsis orchid, soak the bark thoroughly, let every drop drain away, and only water again once the mix is nearly dry and the roots have turned silvery. At an east-facing window, in a 16 cm pot, Verdejar reckons on watering every 6 days in July and every 8 in January.

Why can’t you water an orchid like other houseplants?

The moth orchid (Phalaenopsis) is an epiphyte: in the tropical forests of Asia it grows on trees, its roots exposed to air and to rain that dries off quickly. That’s why it’s sold in pine bark or moss rather than soil. The roots wear a spongy coating that soaks up water in moments but needs air straight afterwards. Missouri Botanical Garden and the American Orchid Society agree on the core of it: the orchid likes steady moisture, but rots if the mix stays waterlogged.

The potting mix changes the sums too. Bark dries far faster than sphagnum moss, which holds water for a long time. If your orchid arrived in a tightly packed plug of moss, expect longer gaps between waterings than in loose bark.

Light and season do the rest. Here are Verdejar’s numbers for the same orchid, in the same pot, in four spots around the home:

Where it lives	In July	In January
South- or west-facing window	5 days	7 days
East-facing window	6 days	8 days
North-facing window	9 days	13 days
Hallway or corner with no window	13 days	18 days

How do you know when a Phalaenopsis needs water?

Orchids have one advantage over almost every other houseplant: in a clear pot, you can see the roots. According to several guides, the American Orchid Society’s among them, plump green roots still hold water; once they fade to a whitish silver, the supply has run out. Michigan State University Extension puts it another way: the roots should dry slightly before they’re wetted again.

Other clues help:

• The weight of the pot. Just after watering it feels heavy; once the bark has dried, it lifts with almost no effort.
• The bottom, not the top. The surface bark dries first and fools you. A wooden skewer pushed to the bottom tells the truth: if it comes out damp, it’s not time yet.
• The leaves. Limp, wrinkled leaves can mean thirst, but also rotten roots that can no longer drink. Always check the roots before deciding.

How to water a moth orchid, step by step

• Water thoroughly. Take the pot to the sink and run water through the bark for a few seconds, or let it soak in a bowl for a few minutes so the bark can take it up.
• Let it drain completely. An orchid should never sit in water at the bottom of a decorative pot or saucer. This is where most of them are lost.
• Use room-temperature water. Very cold water doesn’t suit a plant from warm climates.
• Water in the morning. That way any water that lands between the leaves has all day to evaporate.
• Keep the crown dry. If water pools in the centre of the rosette, where new leaves emerge, blot it with kitchen paper. Standing water there invites crown rot, which both Missouri Botanical Garden and the American Orchid Society warn about.

Should you water orchids with ice cubes?

It’s the advice printed on many orchid labels, and the sources don’t agree. An Ohio State University study found that three ice cubes a week, given to a Phalaenopsis in bark, neither harmed it nor shortened its flowering. Others, Missouri Botanical Garden among them, prefer ordinary watering: ice doesn’t flush out the salts that build up in the mix, and it can damage the leaves or roots it touches.

If you do use ice, set it on the bark, away from the leaves and aerial roots, and every so often give a proper watering to rinse the pot through. Given the choice, a good soak with lukewarm water is simpler and leaves no doubt.

Too much water or too little?

Overwatering is by far the more common mistake. The signs are brown, mushy, hollow roots that fall apart between your fingers, and bark that never quite dries. If that’s what you find, take the orchid out of its pot, trim the rotten roots with clean scissors and repot it in fresh bark. Then leave longer between waterings.

Underwatering shows as roots that stay silvery and dry for a long time, or turn stiff and shrivelled, alongside limp leaves. A good soak fixes it, along with fresh bark if the old mix has broken down and no longer holds anything. For a very different kind of thirst, the soil kind, see how often to water a pothos: it’s the opposite, quick to droop and quick to recover.

At a glance

Situation	What to do
Green roots, heavy pot	Wait
Silvery roots, bark dry at the bottom	Water thoroughly and drain
Water in the centre of the leaves	Blot with kitchen paper
Water in the decorative pot	Tip it out straight away
Brown, mushy roots	Trim the rot and replace the bark
Winter or low light	Leave longer between waterings

Quick questions

Should I mist the leaves? There’s no need, and water lingering between the leaves is exactly what you want to avoid. Watering happens in the bark.

What about the roots climbing out of the pot? They’re aerial roots, normal for an epiphyte. Don’t cut or bury them; when they turn silvery, wet them too.

Should I water less when it isn’t in flower? Go by the roots and the bark, not the flowers. It’s in winter and in low light that the mix takes longest to dry.

Can I use a pot without drainage holes? Only as a cover: the orchid lives in a pot with holes inside it, lifted out for watering.

A plant you water by its roots

Orchids have a reputation for being difficult, but the hard part is resisting the urge to water when the top of the bark looks dry. Plants that prefer to err on the dry side, like the ZZ plant or aloe vera, follow a similar logic. Verdejar does the sums with your light, your pot and the month, and lets you know when it’s time to check the roots. See also the moth orchid page.

Sources: Missouri Botanical Garden · American Orchid Society · Michigan State University Extension · The Ohio State University. The days between waterings come from the Verdejar watering engine.