I recently made the mistake of telling my husband how much my variegated Swiss cheese plants could sell for. The bout of aroid fever gripping the houseplant world has placed these plants at a premium, I explained, meaning my pair of Monstera deliciosa ‘Thai Constellation’ would be a steal at around £150 each.
Like any craze, it’s about supply and demand: variegated monsteras are rare, so people will pay a princely sum to own one. Coleus, on the other hand, must rate as one of the cheapest ways to bring colour to your indoor display. There are hundreds of coleus culitvars in every shade from the sublime to the ridiculous: lemon yellow, lime green, carmine pink, zesty orange and the inkiest purple-black (the coleus flowers, an insignificant pale purple, should be removed on sight as they sap the plant’s energy). And yet coleus had their own gold rush, too. I was fascinated to read in Dr Catherine Horwood’s brilliant book Potted Histories that a dozen new coleus hybrids sold at auction by the RHS in 1868 went for £390 – quite a sum back then.
Over the years Coleus has been no stranger to taxonomic tussles. Until very recently you would have found most coleus described as Plectranthus scutellarioides. Now botanists are in agreement that Coleus, first discovered in Indonesia in 1790, and Plectranthus, first discovered in 1788, are related but distinct genera, and the plant previously known as Coleus blumei then Solenostemon scutellarioides, and now Coleus scutellarioides, is the parent of all the many variously coloured leaf cultivars. Its common name, the flame nettle, comes from its nettle-shaped leaves – not surprising as it is part of the Lamiaceae or deadnettle family.
There are two ways of getting hold of coleus – some cultivars are raised from cuttings, and tend to be sold as plug plants. These are generally slower to flower and set seed, and comprise the more choice cultivars, such as Coleus ‘Saturn’ with its lime-green leaves ringed with red, and Coleus ‘Peter’s Wonder’, the leaves of which exhibit a crazy maze of red, yellow and green. A cheaper alternative is to buy seed to sow in early spring, although the resulting plants tend to be more varied. There are several widely available coleus seed mixes to test out, the most commonly available being Rainbow mix and Wizard mix. The Kong Series has enormous foliage the size of cabbage leaves, while the coleus dwarf mix Fairway is suitable for those with narrow windowsills. Frustratingly, finding some of the more select cultivars in the UK as seed or plugs is not easy; US nurseries offer dozens of coleus with intriguing names, including splashy maroon and green Coleus ‘Religious Rutabaga’ and the magnificent magenta and purple Coleus ‘Mariposa’.
How to grow coleus
- Coleus are thirsty, hungry plants that will reward regular feeding and repotting with abundant growth: if you are accustomed to growing tomatoes, you’ll find they like a similar regime.
- Indoors, light is crucial to their success. It is possible to enjoy coleus all year round, provided you can offer them a minimum of 10°C and a spot by a really large window, or supplement their needs with growlights during winter.
- Without the right conditions they become straggly, and even if you do treat them well, coleus are short-lived plants: they are regarded as annuals by those who prefer to keep them outside.
- As soon as my plants start to look dishevelled, I take copious cuttings, snipping stems just below a leaf node. Packed into a tall glass vase of water, the stems will continue to look pretty until they grow a mass of roots ready for potting up come spring.
Given their ten-a-penny nature of seed-grown stock, it’s worth experimenting with different forms: coleus bonsai, standards and pyramid-shaped specimen plants are all achievable with judicious pinching out. And this is the key to controlling coleus, along with many other fast-growing houseplants. The shoot at the tip of the main stem releases auxin, a hormone that inhibits growth of the side shoots. Remove that leading shoot, and the levels of auxin drop so the plant compensates by sending out side shoots, resulting in a bushier shape.