Beginners, I get it. The world of gardening can sometimes seem like it’s full of vague, even paradoxical advice. Bright but indirect light, moist but well-drained soil… the list goes on. Yet perhaps the biggest paradox of them all is when it comes to wilting leaves, which can rather unhelpfully be a sign either of overwatering or of underwatering, making dealing with them a perplexing problem. So, here is my attempt to cut through the confusion surrounding what I think is probably the number one cause of houseplant failure.
It helps to understand some basic biology. Plants are made up largely of water. In fact, their structures, no matter how complex, are all composed of thousands of cells that are essentially like little water balloons. When these cells lose water to the air around them, they start to soften and shrink, eventually leading to a collapse of their structures. This is the classic wilted appearance we all associate with drought stress. So far, so good, but why would overwatering also cause this reaction?
Well, plants get the water they need to keep their cells plump and hydrated from their roots. Yet these roots need a mixture of both water and air in the soil to keep healthy. When overwatered for long periods of time, all the air spaces in the growing media become saturated with moisture, depriving the roots of the vital oxygen they need. The low-oxygen environment also fosters the growth of anaerobic bacteria that can cause the plant’s roots to rot and eventually die. This damage paradoxically hampers the plant’s ability to absorb water, leading it to display the symptoms of drought stress.
Given that the above-ground symptoms of overwatering perfectly mimic those of drought, the natural reaction of many growers is to pour even more water on them, creating a vicious cycle and you end up killing them with kindness. Most houseplant deaths, judging by the sorry specimens people show me, are from overwatering, usually the result of this confusing catch-22. The silver lining is that once you know this is a common problem it is very easy to avoid.
As a general rule, I’d say if in doubt, avoid watering, as it is usually far easier to sort out a thirsty plant (most will return to normal within minutes of watering) than coax an overwatered plant with damaged roots back from the brink. There are two ways to spot whether a plant needs a drink. The first is to scratch away the top inch or so of the growing media and stick your finger in to see if you can feel moisture. The second is to take a look at the colour – most conventional potting mixes will be dark and crumbly when moist, and lighter brown and dusty when they need watering. If you need further confirmation, pick up the plant to feel its weight. If the pot feels light for it’s size on top of these symptoms, it’s likely watering is needed. Don’t go by the leaves alone!
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