Houseplant Appreciation Day

What the day is

Houseplant Appreciation Day is observed on January 10, immediately after the decorations come down and the house looks bare, which is presumably the point.

Origin and background

The origin of the observance is not documented. The most repeated claim about houseplants is worth examining, because it is essentially wrong.

A much-cited study from the late 1980s placed potted plants in sealed chambers with volatile chemicals and measured the concentration falling. That finding became the basis for decades of confident advice about plants purifying indoor air. The problem is the sealed chamber. A real room exchanges air with outside continuously, through vents, gaps and doors, and that exchange removes contaminants vastly faster than foliage does. A reanalysis published in 2019 worked out what it would take for plants to match ordinary building ventilation and arrived at densities in the range of tens to hundreds of plants per square meter. Opening a window for a minute does more than a shelf of pothos does in a week.

What holds up better is psychological. Studies of indoor greenery report modest but fairly consistent improvements in mood and in attention restoration, and the effect of tending something living is not nothing in January.

The practical knowledge matters more than either. Overwatering kills far more houseplants than neglect, because roots need oxygen and saturated soil suffocates them, producing drooping leaves that look exactly like thirst and prompt more water. Light is the other misjudgment. Brightness falls away steeply with distance from a window, so a plant a few paces into the room is in much deeper shade than it appears to a human eye, which adjusts and does not notice.

How to take part

• Check the soil with a finger before watering, every time.
• Water less in winter. Low light means slow growth means little water needed.
• Move plants closer to the window for the dark months.
• Dust the leaves, which are the plant's solar panels.
• Buy one that matches your light rather than one you liked in the shop.
• Open a window occasionally. That is the actual air purification.