Watering and feeding your moth orchids – an expert guide

From overwatering to underwatering, I’ve been there, done that, and my poor orchids have come along for the rollercoaster ride. I learned the hard way.

Unlike many of the other 100 or so plants in my indoor jungle however, I find orchids one of the easiest to read once you know what to look for.

When to water your moth orchids

One trait orchids do share with other houseplants is that watering on a schedule won’t always work. However, Greg Barnes – a member of the New Zealand Orchid Society, Greg Barnes also runs a plant products business called Bio Leaf – finds that, “as a rule of thumb, during summer and active growth, water two to three times a week if your orchid’s in a good quality, free-draining, bark-based mix. As substrate holds water longer in winter, that may change to every 10 days or so in cooler months.”

Grace Cattermole from Gellerts, an Auckland-based commercial nursery who have been growing and selling orchids for over 20 years (they specialise in the Phalaenopsis with more than 100 varieties imported last year alone from growers and breeders worldwide), finds overwatering or underwatering the biggest issue beginners struggle with.

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“The roots of a Phalaenopsis are always a great indicator of how the plant is doing,” she says. “If they’re plump and green you’ve got the watering just right. If they’re starting to go silver then your orchid wants a drink. If they’re a silvery-brown and starting to shrivel, they need a really good drink!”

One of many orchid tips I learned from my mother is to use fish tank water for my plants. A huge 260-gallon tropical aquarium has pride of place in my parent’s home. Fish tank water naturally accumulates nitrogen, phosphorus, potassium and other minerals, plus has the added benefit of already being warm. Although it doesn’t replace the need for fertiliser, it gives plants a gentle dose of some of the many essential minerals they need.

Temperature is also important when it comes to watering. The most common orchid myth I remember from the early days is to water with ice cubes. This myth came about from good intentions to reduce overwatering and is still doing the rounds today.

One problem is it leads to underwatering. The other is the shock of ice cold water on the roots can damage or even kill them. Best to stick to warm water and save the ice for your drinks, not theirs.

I no longer have a fish tank myself, but have always found regular tap water fine for my orchids where I live.

However, one exception is water softened with salts. Orchids tend to be more salt sensitive than other houseplants, and some genera are especially sensitive (for those, I’d avoid tap water).

My orchids would envy yours if you use rainwater, but if that’s not an option for you, you can use tap water left to stand uncovered overnight. This not only helps regulate the water temperature to match the ambient temperature, reducing temperature shock for the roots, but also allows the chlorine added to tap water to gas off.

Lois Dougherty is the President of the Wellington Orchid Society and has kept orchids for 50-plus years with around 3000 orchids in her collection. She suggests bottom watering by “filling a basin with water that reaches the top of the pot and leaving it for a while, so the bark soaks up the water.”

If there’s one thing orchids dislike, it’s wet feet. When bottom-watering, I soak mine for about 30 minutes, but whether you water from above or below, I always make sure my orchid is fully drained, and never leave water sitting in the saucer or cover pot.

It’s not just the roots that signal when to water. As well as changing colour in response to different light levels, Phalaenopsis leaves also show you when the plant is thirsty. Like roots do, leaves will also start to wrinkle and look leathery when thirsty, or even go soft and start to wilt if left dry too long.

As well as roots and leaves, the trifecta for knowing when to water Phalaenopsis is to wait until the substrate has almost fully dried out. I prefer to water before the leaves wrinkle so you’re not drying the plant out too much, but you’ll quickly get a feel for the right timing. If in doubt, I’d wait a bit longer. Watering again too soon is much worse and caused me to lose more than one orchid to root rot in the early days.

Another tip to help avoid the dreaded rot is to water in the mornings. This allows time for excess water to evaporate during the day. Even with watering at the right time of day, it’s best to avoid water sitting on the leaves or in the crown too long. I inevitably manage to wet the crown when I water, so I keep paper towels or cotton buds on hand to wipe away stray water droplets, especially in winter when water takes longer to evaporate, and the risk of rot goes up.

Give the pot a little lift when you pass your orchid and before long you’ll get used to the “wet weight” of the pot and will know just by lifting it when it’s time to water again.

I wish clear pots had been available when I first got into orchids. I wouldn’t be without them now. Not only can you see the roots and substrate change colour as they dry out, but you can also see condensation droplets on the inside of the pot. Once there’s almost no condensation, that’s another sign your substrate has almost dried out and it’s time to water your Phalaenopsis.

Once you know the many signs to look for, getting watering right becomes easy.

What to feed your orchids, and when

Don’t be like me. At first, the fear of fertiliser burn caused me not to feed at all, but water, warmth and light were not enough. Failing to fertilise turned out to be the cause of my ongoing battle with yellowing lower leaves in the early days.

Specialist orchid fertilisers are now available that reduce the risk of fertiliser burn.

I used to give my orchids a thorough top water drench with plain water every month or so to help flush out excess salts, which can otherwise build up over time and scorch the plant. Like limescale spots on your shower glass, one sign salts are building up is a white or brownish crust on the substrate and around the pot. Over time, those excess salts from tap water and fertiliser can burn roots and cause brown leaf tips. Left too long, the damage can be fatal.

These days, I use a fertiliser that avoids burning the roots, so I don’t have to do a flush like I used to. I feel like I’ve tried them all over the years, and brands I recommend are Dyna-Gro and Growth Technology. Both have specialist orchid formulas.

You’ll often find brands make a formula for foliage, and one for flowers. Shift your orchids onto a flower or bloom fertiliser around autumn, before the flower spike appears, and keep feeding until flowering finishes, then shift to a foliage formula to support root and leaf growth.

Wellington Orchid Society’s Lois Dougherty fertilises her 3000 orchids every time they’re watered, often called the weakly-weekly method. Although not literally weekly, it simply means to feed lightly, every time you water. That’s weekly in summer and less in winter, but as Phalaenopsis don’t go dormant in winter, do keep feeding them lightly all year round. This reduces the risk of both excesses and deficiencies.

A deficiency in an essential mineral can cause problems such as bud blast, where buds form but fail to bloom; one cause being not enough calcium – another ingredient to research when choosing your orchid fertiliser. Not all fertilisers include calcium which is essential for orchids.

Anna Gervai runs an online one-stop-shop for houseplant hobbyists, Love That Leaf.