Overwatering

 If there’s one phrase I use most frequently, it is “well-drained soil”, and eyes probably gloss over on reading it. I repeat it because it’s one of the most important pieces of advice, for most garden plants and particularly for houseplants. 

It is, of course, a somewhat general term as clearly there are plants that do not want a well-drained soil; waterlilies and bog plants, for instance, and there are long lists of plants that don’t mind having their roots in permanently moist soil; however, moist is not the same as waterlogged. Water is essential for all plants, but roots need oxygen as well as water, and waterlogged soil has little room for air. Soil that drains well ensures there are air spaces around the plant’s roots.

Most people will use store-bought potting soil, also referred to as a soilless mix, yet quality can vary considerably. The better ones will list the ingredients, typically peat moss, coir, or sometimes composted organic material. Perlite is usually added for drainage, vermiculite for water absorption, and lime to balance the pH. 

If a fertilizer supplement is included, it should be listed on the label under Guaranteed Analysis. Some soils will be labelled as sterilized or pasteurised, which ensures the mix is free of bugs, weed seeds and possible pathogens. This is especially important for starting seeds.   

Along with well-drained soil is the advice about not overwatering, and the two go together.  Other than ignoring a houseplant until the leaves have wilted and turned brown, the biggest reason houseplants expire is too much water, which causes roots to rot. Even when the soil does drain well, if there’s nowhere for excess water to go there’s still potential for rotting to occur. This is typically what happens when a pot is wrapped in foil or sits for days in a water filled dish. The soil then stays saturated even though the surface can appear dry.

There’s still a belief that adding gravel or similar to the bottom of a pot helps, but it isn’t recommended. All it does is reduce the depth of the soil in the pot. Soil acts like a sponge. Once saturated, excess water flows out into the gravel where it cannot be easily reabsorbed by the soil above. 

Meanwhile, thanks to gravity, the lower part of the soil will retain most of the moisture. It will be gradually drawn upwards by capillary action, but when the soil depth is reduced by the addition of gravel, it means the roots of the plant are more likely to be in this wetter zone where there’s a lack of oxygen. 

So what’s the answer to correct watering in the care of houseplants? Consistent attention is important, but first know your plant and what its particular needs are. Some like to dry completely between watering while others prefer the soil to be slightly, though consistently moist. 

A general rule, however, is to water thoroughly then allow the soil to almost dry out before watering again. I say almost because even though plants like succulents can handle completely dry soil for a short while, and even prefer it, you’ll soon be calling the undertaker for others. 

Wilting leaves is a clue but wilting leaves can indicate other problems, so again, check the soil before watering. A dry surface doesn’t mean the soil below is dry, so poke a finger into it. There are moisture meters for this, but there are questions about their accuracy, so I much prefer to use my genuine digital approach. I’ll also heft the pot because the weight is a good indicator of moisture levels.

One more time — well-drained soil, know your plant, and check it daily.