I was wrong and (some of) you were right!
For years, I’ve been telling home gardeners not to water their orchids with ice cubes, mostly based comments by orchid experts, but also on the logic of the situation. It just didn’t seem to make sense to me to water a tropical plant that hates the cold with melted ice cubes. However, the first ever (as far as I know) scientific study has been carried out and it turns out you can!
According to Ice Cube Irrigation of Potted Phalaenopsis Orchids in Bark Media Does Not Decrease Display Life, a study done for the American Society for Horticultural Science by Kaylee A. South, Marc W Van Iersel, Paul Thomas and Michelle L. Jones and released in September, 2017, no harm came to potted phalaenopsis by watering them with ice cubes and they remained in excellent condition throughout the test. This was compared to watering from above with an equivalent volume of room-temperature tap water, which gave similar results.
Their tests show that, by the time the water has permeated the growing mix (here, only bark was tested, but one can assume the same would occur with other substrates), it has warmed up enough not to cool it to any great degree. The study showed the lowest temperature in the orchid bark media was more or less 11˚ C. Also, even when aerial roots were in direct contact with ice cubes, their core temperature did not drop below 4˚ C. They studied how much cold phalaenopsis roots could survive and found they could resist as low as -7 ˚ C when plunged rapidly into an antifreeze bath.
Watering with ice cubes was not without its risks, though. The researchers cited other studies showing ice cubes damage phalaenopsis leaves if they remain in contact with them. One study showed permanent leaf damage at only 10˚ C, suggesting the leaves are much more sensitive to cold than the roots. The authors of the ASHS study recommend to only place ice cubes on the roots and the substrate, never on or against the leaves and suggest there was plenty of room for this. Oddly, the photo accompanying the report shows exactly what not to do: the ice cubes are touching the leaves, plus, in the case of the phalaenopsis shown, there really was no room where you could legitimately place ice cubes without touching the leaves. Obviously, if you intend to water your phalaenopsis using ice cubes, you have to carefully choose plants where there either is a lot of exposed substrate or exceptionally narrow leaves.
Even with that warning in mind, ice cubes, it turns out, are simply not the enemy I thought they were. The root damage I had always assumed must necessarily occur when cold water drips slowly over tropical roots simply did not occur.
Will This Information Change the Way I Grow Orchids?
I have no intention of changing my own method of watering orchids, both phalaenopsis and others, that is, by soaking their roots in water, then letting them dry out before soaking them again.
In the now distant past (about 40 years ago), I used to water my orchids from above (the method this study compared ice cube watering to) and found that method inefficient and harmful, leaving lower roots drought-stressed (if the excess water was removed from the saucer too quickly) or rotting (if the plants were allowed to sit for days in a saucer of water), with many dead roots accumulating over time in both cases.
When I repot orchids watered by soaking the roots, then providing good drainage, ensuring that all of them get equal moisture, compared to orchids watered from above, I find (and yes, I admit this is anecdotal evidence: I have not done a proper study) there are many fewer dead and dying roots in the “soaked” orchids. Judging from the photos I’ve seen of people repotting orchids watered using ice cubes, they too seem to show more dead and dying roots compared to phalaenopsis watered by soaking.
What About Future Blooms?
What this study does not cover at all is how watering with ice cubes affects the plant’s overall health and its capacity to rebloom. This was not even a consideration in the ASHS study. It seemed designed to reassure professional orchid growers, most of whom make their living selling blooming phalaenopsis to amateur gardeners and for whom the ability of their orchids to rebloom in the average home is of little interest, that they can legitimately sell “ice orchids” without feeling guilty about it. Yet I almost never run into home gardeners who toss their orchids into the compost after they stop blooming: most want to see the plants bloom a second time … and a third, and a fourth! Nothing about the study suggests that ice cube irrigation either helps or hinders the orchid’s ability to rebloom. It’s as if the study ended about four years too early!
At any rate, the real question is whether watering with ice cubes is better than soaking orchids, not watering them from above, and not only for the first blooming cycle, but over many years. In my opinion, the researchers asked (and answered) the wrong question!
Too Laidback to Water With Ice Cubes
Besides, my laidback mind has a hard time bending around the idea that I’d be freezing water so just it would unfreeze. That just doesn’t seem right. Also, the ice cube method involves more work: the extra effort of having to fill cube trays with water, then having to make trips back and forth from the freezer to “harvest” ice cubes: that would be needlessly time-consuming. And I have to wonder about the environmental impact of freezing water for such a frivolous purpose: wouldn’t that waste electricity?
And finally, the really important question: the degree of domestic strife ice cube watering could cause. Imagine the frustration of discovering the ice cube tray empty just when you need ice cubes for your orchids because someone in the household (and we all know who) mistakingly thought the purpose of ice cubes was for cooling drinks!
So, mea culpa, I was wrong in saying you shouldn’t water orchids with ice cubes. If you want to, go right ahead. They’ll probably hold on to their flowers just as long as they would if you watered their roots by pouring water over them and I’ll bet they’ll rebloom just about as readily too. However, I now await a study comparing the difference between watering phalaenopsis by soaking (the method recommended by orchid experts) compared to conventional watering or placing ice cubes on their growing mix.
So, orchid researchers, any takers?