How to Water a Cymbidium: A Thirsty Orchid in a Coarse Bark Mix

Forget everything you know about watering a moth orchid

A phalaenopsis is an epiphyte that clings to a branch, dries out completely between waterings, and rots if it stays wet. A cymbidium is a semi-terrestrial plant that grows in leaf mold and grit with a huge root system, and it is thirsty. In a hot outdoor summer a mature plant in a ten inch (25 cm) pot can need watering every day, and that is normal rather than a sign that something is wrong.

The mix is what makes this safe. Cymbidiums are grown in coarse bark with grit or perlite through it, so water pours straight out of the base and air comes in behind it. In that kind of mix you cannot easily overwater a growing plant by watering too often; you overwater it by leaving the pot standing in a saucer of water, or by using a fine peaty compost that stays sodden. The frequency is not the problem, the drainage is.

The other half of the rule is the winter half. When the plant is cool and either in bud or in flower, growth slows and so does water use. The same pot that needed water daily at the peak of summer growth may need it once every ten to fourteen days in a 50F (10C) room. Keep watering at summer frequency through a cold winter and the roots turn brown and hollow. Cut water back to nothing at all and the buds blast and the pseudobulbs shrivel. Neither extreme is right.

Deciding when to water

There is no fixed interval, because the answer depends on the season, the pot size, the weather and how root-bound the plant is. Judge it from the pot rather than the calendar. Push a finger an inch or two (3 to 5 cm) into the bark: if it feels cool and damp, wait; if it is dry and the bark chips feel light and papery, water. Lifting the pot works even better once you know what a freshly watered plant weighs.

A wooden skewer pushed to the bottom of the pot and pulled out is the most honest test in a deep pot, because the base can still be wet while the surface has dried in the sun. A skewer that comes out dark and damp means wait. One that comes out dry and clean means water now. Leave it in place and check it whenever you pass.

Watch the pseudobulbs as your longer-term gauge. Fat, smooth, firm bulbs mean the plant has enough water. Bulbs with fine vertical wrinkles are running short, either because they are not being watered enough or because the roots have died and cannot take water up. Wrinkling on a pot that is constantly wet is a root failure, not thirst, and the answer there is to unpot and look rather than to water more.

How to water so the whole pot gets wet

Coarse bark in a root-bound pot channels water down the sides and out of the holes without wetting the middle, so a quick splash leaves the core of the root ball dry. The cure is volume and repetition rather than a longer trickle.

1. Water in the morning Morning watering lets the foliage and the leaf axils dry through the day. Water sitting in the crevices between leaf bases overnight in cool weather is how bacterial and fungal rots start.
2. Pour slowly over the whole surface until it runs from the base Use tepid or ambient temperature water and cover the entire surface of the mix, not one spot. Keep going until water flows freely out of the drainage holes.
3. Wait a minute, then do it again The second pass is what wets the center of a root-bound pot. Dry bark repels water on first contact and only absorbs it once it has been dampened, so a single pass regularly leaves a dry core.
4. Let it drain completely before it goes back Stand the pot up on feet or on a grid until dripping stops. Never leave a cymbidium standing in a full saucer or a cover pot with water in the bottom.
5. In hot weather, soak the pot instead Once a fortnight in summer, stand the pot in a bucket of water up to the rim for twenty minutes, then lift it out and drain. This rewets a badly dried root ball that surface watering can no longer penetrate.

Water quality, feeding and flushing

Rainwater is ideal, and outdoors in summer a plant standing where it catches rain waters itself for much of the season. Tap water is acceptable in most areas; where it is very hard, the visible risk is a white crust of lime on the bark and the pot rim and a gradual rise in salts around the roots. Softened water run through a domestic ion-exchange softener is the one to avoid, because it swaps calcium for sodium, which builds up in the mix.

Cymbidiums are hungry as well as thirsty, and feeding rides on the watering. Use a balanced orchid feed at every second or third watering from the start of growth in spring through midsummer, then switch to a low-nitrogen, high-potassium feed from late summer through autumn to harden the growths and support the spike. Stop feeding almost entirely while the plant is cold and in flower, and start again when new growths move.

Because you are feeding often, flush the pot with plain water every fourth or fifth watering, running two or three pot volumes through until it pours out of the base. That washes out accumulated fertilizer salts, which otherwise burn the fine root tips and show as blackened root ends and brown, dead leaf tips.

Brown, dry leaf tips on an otherwise healthy cymbidium usually mean salt build-up or a spell of drought at the root, not disease. Flush the pot thoroughly, correct the interval, and watch the newest leaves. The damage on old leaves stays, but new growth should come up clean.

Reading the difference between too dry and too wet

The two failures look alike at a glance, because a plant with rotted roots cannot drink and so shows the same wrinkled bulbs and limp leaves as a plant that has been left dry. The difference is in the pot. Tip the plant out and look: healthy cymbidium roots are thick, white or cream, and firm, with a solid core you can feel. Dead roots are brown or gray, collapse when squeezed, and pull apart to leave a wiry thread inside the sleeve.

If the roots are sound and the bulbs are wrinkled, the plant is simply thirsty and the interval is too long. If the roots are hollow and the mix smells sour or feels like wet sawdust, the mix has broken down and stayed saturated, and the plant needs repotting into fresh coarse bark rather than a change to the watering can.

Keep a rough note through the year of how often you actually watered in each season and what the weather was doing. A cymbidium's needs shift enormously between a hot exposed summer and a wet one, and a season of notes turns watering from guesswork into something you can repeat. It is also the fastest way to spot the year a pot's mix has collapsed, because the interval suddenly stretches out for no visible reason.