Of all the succulents, string of pearls (Curio rowleyanus) is one of the most distinctive and most sought after, adored for its cascade of wiry stems festooned with tiny spherical leaves that look like peas (or beads or pearls, if you are feeling poetic). But if I could do one thing in the service of horticulture, it would be to end the tragic deaths of string of pearls plants at the hands of their owners.
Within weeks, the pearls are shrivelled or turned to mush, and the befuddled owner just can’t fathom why – they watered their plant at the same frequency as their other succulents, placed it in the same sunny windowsill, and yet it will not thrive.
Curio rowleyanus (you may recognise it under its previous name of Senecio rowleyanus) is found only in the Karoo shrubland of South Africa’s southern cape although other species are found as far north as Namibia. Despite its characterisation as a trailing plant in cultivation, in the wild string of pearls forms a mat on the ground, often growing beneath and over shrubs and other plants or lodging in cracks in rocks, rooting along its stems where it can find a suitable spot.That provides an important clue as to where things go wrong with this plant in the home: it is adapted to grow in sharply drained soil that is low in humus.
How to care for string of pearls
When bought from a garden centre or online shop rather than a specialist grower, string of pearls usually arrives in a plastic hanging pot with a built-in saucer, planted into regular houseplant compost (if you are particularly unlucky, this will already be sopping wet). It’s not long before poor drainage and spongy soil allows water to build up around the roots, and the plant will start to protest.It’s wise to repot plants as soon as possible into a gritty mix of a third to a half grit or perlite and a similar quantity of John Innes No.2. I find a terracotta pot rather than a plastic one helps to keep the roots happy. With these measures in place, plants can be generously watered once a week in summer without risk of damage. From November onwards, cooler temperatures combined with minimal watering keep string of pearls ticking over until spring.
What about light? In the wild this plant doesn’t usually grow completely exposed to the sun, but of course the intensity of the light is hugely greater there than the average sunny windowsill in a British home. My string of pearls plant grows contentedly on a high shelf in my glass-roofed, north-facing sunroom, where it gets lots of bright light: plants may need some shading if they are grown in a greenhouse or outside during the hottest months. The cream-striped variegated form seems more susceptible to sun exposure, so take extra care if you are lucky enough to own one of these.
It seems churlish not to mention the flowers. Small, white inflorescences appear along the stem in summer, making their presence known via a cinnamon scent rather than dramatic looks. They are, however, most likely the only way you’ll ever know that string of pearls is a member of the daisy family (Asteraceae).
How to propagate string of pearls
Once you’ve cracked caring for Curio rowleyanus, you can play Lady Bountiful and root some cuttings for admiring friends. The simplest way to do this is simply loop the stems back on to the surface of the compost until they root and can be snipped away.
Once your plant is happy, and you are no longer afraid to look at it sideways in case it keels over, it is worth examining it more closely. Like many succulents, the string of pearls plant has found a way of adapting to its arid environment through its leaves. Reach back to maths class at school and you may recall that a sphere has the lowest surface area to volume ratio of any shape. By having spherical leaves, string of pearls can store the maximum amount of water possible. At the same time, there’s less surface area through which water loss (transpiration) can occur, and less leaf exposure to the midday sun, reducing the prospect of the leaf getting frazzled by the heat.
But what about photosynthesis, you may wonder – surely reducing the surface area of the leaf means string of pearls won’t receive enough light? The plant has another clever trick for that. Each leaf contains a darker strip that’s visible when held up to the light. This is an epidermal window, which seems to work by allowing light to pass into the inner tissues of the leaf where photosynthesis can occur. I write ‘seems’ as botanists are still investigating exactly how these windows function. These fascinating plants may yet have more secrets to reveal