Costus malortieanus, commonly known as the Step-ladder Costus is an interesting spiral ginger to grow. Native to northern South America and central America, this particular species produces only a few leaves on a short pseudostem. Typical of members of Costaceae, its leaves are arranged in a spiral manner, making each leafy shoot look like a propeller when viewed from the top.
In terms of its growing conditions, this Costus species prefers to be grown under shadier conditions outdoors than most others. When growing conditions are ideal, its leaves take on an emerald green colour with darker lengthwise striations. They are quite nice to feel as each leaflet is densely covered with short soft hairs.
Like many other similar spiral gingers, I noticed Costus malortieanus usually grow up to about 2 feet (60 cm) in height, when it is grown under semi-shaded areas outdoors where the plant receives filtered sunshine, although there are sources on the Net that indicated it can grow up to 3 feet (90 cm) tall. Under brighter conditions, the plant usually becomes shorter but the emerald green colour on this spiral ginger’s leaves fade to a pale, unappealling and sicky light green colour. The striations also disappear altogether.
Costus malortieanus prefers to be grown in fertile, well-draining soil that is also moisture-retentive. Its roots need to be kept moist but not wet at all times. It seems to be particularly sensitive to drying out and it is best to grow plants in shady locations protected from wind. Plants can, fortunately, tolerate a couple of hours of direct mid-day sun, as long as the soil is kept moist. Moisture-stressed plants respond by droopy leaves that make each leafy shoot appear like a closed umbrella. Prolonged drought sets plants back severely.
Costus malortieanus produces flowers on a bright green, fat cone-like inflorescence.The bracts on its cone are tightly clustered together, making it look smooth with no obvious scales. In my opinion, the inflorescence of Costus malortieanus is not particularly showy like those produced by a handful of other Costus species. Flowers appear from between the bracts and are bright yellow marked with red stripes.
In Singapore, Costus malortieanus is not a plant that is commonly or easily available. For those of us who are familiar with spiral gingers, one would have noticed that non-flowering specimens of Costus malortieanus look very much like Costus curvibracteatus (sometimes referred to as Costus productus). Costus curvibracteatus is a commonly used local landscaping projects valued for its showy orange cone of bracts.
As a result, Costus malortieanus often gets mixed together with Costus curvibracteatus that are sold in local nurseries. This manifests itself in various local landscapes which I have come across, such as the one shown above – a border of low-growing costus at the KHA restaurant at HortPark. Individuals of Costus malortieanus grown together with Costus curvibracteatus only become apparent when they start to flower.