Killing them with kindness - when watering isn’t wise

When in doubt do not water your houseplants, James Wong says. PHOTO: GETTY IMAGES
When in doubt do not water your houseplants, James Wong says. PHOTO: GETTY IMAGES
To water or not to water? The rules for looking after houseplants can seem like cryptic riddles. But it all boils down to one thing: don’t give them too much.

There are some pieces of gardening advice that can seem incredibly frustrating and confusing, even contradictory. From the ubiquitous "bright but indirect light" needs of seemingly every houseplant to the "keep moist but not wet" advice for watering, instructions can seem like cryptic riddles.

Perhaps the most common frustration I hear from my non-planty mates is why the internet is so keen to diagnose wilting leaves as an always "clear" confirmation of either over-or under-watering. For many, it’s far from clear.

To help cut through the confusion, here’s a quick plant science lesson on wilting leaves.

First, most of you will know that plants absorb water through their roots. However, what we often talk less about is that the roots of the majority of species also require oxygen as much as they do water. They absorb this through tiny open spaces in the growing media called macropores. When you totally saturate the compost for long periods of time, you flood these macropores, starving delicate roots of their oxygen.

This low-oxygen environment also creates the perfect habitat for pathogenic microbes to thrive. A double whammy of weakened roots and boosted microbial count can quickly cause roots to rot away. This is particularly the case for species from more arid parts of the world that have little or no evolutionary adaptations to these boggy conditions.

Once these roots start dying away, the water uptake to the plant’s leaves is hampered, causing them to display the same symptoms as plants that have been underwatered. Therefore, take wilted leaves as only one of the clues in your diagnosis. Does the soil also feel dry to the touch when you scratch the surface? Does the plant feel light for its size when you pick it up? If so, it’s thirsty.

If the answer to these two questions is no, then it’s probably a case of overwatering. Treating this will involve removing the plant from its pot, cutting away any soft, brown or bad-smelling roots, and potting it back up in fresh compost.

The takeaway from this lesson? If in doubt, do not water. This is particularly the case in winter when lower light levels mean the plants aren’t growing as quickly and therefore require less moisture. Thirsty plants can usually be made happy again in minutes by simply adding water, whereas plants that have had their roots compromised by disease are much harder to coax back to health.

As too much love is probably the single most common cause of houseplant failure, the great news is that generally doing less will give you better results.

- By James Wong

- Guardian News and Media


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