All summer long, I can be seen enacting a madcap dance in my sun room: feather duster held aloft, trying to shoo a cloud of pollinators out through the French doors. I do love flying insects, from dainty parasitoid wasps to those furry dirigibles of the garden, the bumblebees, but I prefer them outside, not beating uselessly against the glass roof. If anyone can explain the transatlantic anomaly that means every North American home is fitted with fly screens as standard, while they are pretty much unheard of in the UK, I’d appreciate it.
I take some small comfort in my discovery that some of the smaller flies that enter may end up taking an enforced break inside the flowers of the string of hearts (Ceropegia linearis subsp. woodii) that trails from a high shelf in the corner. ‘String’ is an accurate common name for this plant, whose thin wiry stems can easily reach a metre or two long, adorned with opposite pairs of fleshy, dark-green, heart-shaped leaves inscribed in silver. Small pinky-purple flowers appear along the stems every summer.
The Ceropegia flowers – I can’t help thinking of tiny turkey basters when I look at them – are tube-shaped, topped with a hairy cage structure. Botanists aren’t exactly sure how the flies are tempted inside, although a prominent theory is what’s known as ‘brood site deception’, which means that the flies are fooled into thinking it’s their favourite spot to lay eggs, and end up trapped in the tube by hairs so aligned that they cannot escape the way they entered. This isn’t carnivory, just tenacious pursuit of pollination: once the short-lived Ceropegia flower starts to fade, the flies will be released.
These feats of pollination go largely unnoticed, because it is the string of hearts’ pretty foliage and ease of cultivation, not its flowers, that have made it such an enduringly popular house plant. Like most of the other 200 or so species in the genus Ceropegia, string of hearts grows wild in southern Africa, where it scrambles around the semi-arid landscape and roots into the ground where it can. In our homes, its flexible stems can be allowed to trail to great lengths, or trained around a hoop or even a picture frame, but take care not to get them tangled: unknotting a mass of Ceropegia strings is a thankless task.
Ceropegia cultivar choice
A few cultivars are available: ‘Lady Heart’ offers leaves irregularly edged in cream, while ‘Silver Glory’ has heavily silvered foliage. Other species from the genus are harder to find but equally fun to grow, such as Ceropegia sandersonii with flowers that look like green parachutes, and Ceropegia ampliata with its strangely bare succulent stems and white and green blooms. String of hearts is probably the most popular, though, because it is just so tolerant of a wide range of conditions. Its stems spring from a tuber that can reach the size (and the look) of a potato in older specimens: another common name, rosary vine, stems from the plant’s habit of growing more of these tubers in miniature along its stems.
How to look after your Ceropegia plant
Ceropegia will thrive in shade and bright light (though it should avoid hours of direct sun), and draw on the reserves of its tubers to survive weeks without water. The only realistic way of killing this plant is potting it up in a drainage-free container in heavy compost and leaving the tubers to turn to mush. Instead, provide a free-draining potting mix by adding a good handful of grit or perlite to your regular house plant compost, and the plant can be watered weekly in the growing season. Ease off in the winter, only watering when the compost is really dry. Then, your only real problem is what to do when your string of hearts reaches the floor.
How to propagate Ceropegia
The quickest way to propagate plants is to check your plant for the potato-like aerial tubers that often stud the stems. Snip these away just above the tuber and plant them just under the surface of a pot of gritty compost, and they will root almost immediately. If you aren’t graced with any tubers (some plants just don’t seem to produce them), cut away some stems and place into a glass of water to root: it will take a little longer, but the result will be the same. If your Ceropegia plant looks a little sparse, you can even plant rooted stems or aerial tubers back into the original pot to make a more abundant display.