About the genus
There are over 600 species in this genus, spread throughout the tropics and subtropics. Some species are considered invasive as their vines can grow to over 18m in length but that is not a problem with the plants that we see in cultivation. Dioscorea are perennials with tuberous roots or caudices (swollen stem bases), climbing stems and small, yellow-green flowers.
There are three species that we commonly see in cultivation and they all make great plants for the home or greenhouse. These are caudiciform plants (a fat, short, swollen stem is referred to by collectors as a caudex, while plants that display this kind of growth habit are called caudiciform). Dioscorea have a deeply fissured surface, resembling an elephant’s foot, hence their common name.
Most species are dioecious, each plant having either male and female flowers, so you will need two or more plants to produce seed which is a really fun way to grow these plants.
How to grow them
Dioscorea elephantipes is the most popular plant that we see in collections and originates from South Africa (Cape Province) where the caudex can become large, but in cultivation they will not outgrow their welcome.
In nature they grow under shrubs and this is a clue to successful cultivation. In summer, plants will become dormant and it is a good idea to give the caudex some shade under the staging. Sun will not kill the plant but it will leach the lovely brown colour out of the caudex and it will in time become silver, just like wooden garden furniture.
During this dormant period an occasional watering stops them drying out too much and usually encourages them to come into growth a little earlier than if kept totally dry. In late summer, move the plant into a bright position and increase the watering once you see the twining, fast-growing vine emerge from the top of the caudex. Do not forget to feed your winter-growing plants but also remember that plants do not dry out as quickly in the winter. A cane is often a good idea to support the twining vine, and remember to look out for the tiny yellow flowers that can be easily missed because of their size. At the end of the growing season (spring) the leaves start to turn brown and at this point the vine can be removed.
It is an easy plant to grow from seed. I usually push the seed slightly under the surface. It will only germinate in coolish conditions and I find that 15°C is about right. After a short time, you will see some top growth and a small vine will develop. At this stage do not expect to see the caudex as this will grow well out of sight underground. As the seedling grows the caudex will slowly emerge.
Dioscorea sylvatica is a very similar plant but I find its caudex is less fissured. Dioscorea mexicana is also a similar plant but this is summer-growing and needs to be watered at the same time as our cacti.
Text and photos by Ian Thwaites
No part of this article may be reproduced without permission. Copyright BCSS and the Author 2024