Houseplant owners are advised that windowsills, despite offering maximum sunlight, can become dangerously cold for plants during winter. The glass itself can get cold, and heavy curtains can create a cooler area around the window.
This cold can be particularly harmful, even fatal, for tropical plants like anthuriums and philodendrons, which are accustomed to more stable temperatures. One suggested method to protect these sensitive plants is to move them back from the glass overnight and return them to their brighter position in the morning.
A test conducted in a centrally heated home with double-glazed windows showed that windowsill temperatures could drop to around 15C overnight in unheated rooms. Delicate tropical plants benefited from being moved away from the cold windowsill, while hardier cacti were unaffected. Preventing foliage from touching cold glass also reportedly reduced leaf damage.