The first instalment of the Root Awakening column for 2010 was published today.
The first question dealt with white insects on kangkong plants and this could be an infestation of white flies. To eradicate these pests, spray plants using white summer oil or neem oil. Make sure you cover every part of the plant thoroughly, including the leaf undersides as well as any spaces between leaves. There is also a need to repeat application of the pesticide several times to ensure all progeny that hatch from eggs laid earlier are also eradicated. Check surrounding plants for any signs of infestations as well. Pests from these plants can migrate over at times. They should be sprayed as well if there is any signs of infestation. Alternatively, this could be a fungal disease called white spot that commonly occur in kangkong plant. Note that the spots are not mobile and cause the upperside of leaves to have yellow spots.
The second question was about the growing of the rangoon creeper in a container. Note that the Rangoon creeper is a big vine and it may not be a good idea to constrain it in a pot as it will be likely to suffer from water stress. A plant that has grown larger with a dense crown of foliage tend to have a higher demand for water as it transpires more. The amount of water that can be retained by the soil in a pot may not be sufficient for the plant’s needs. A plant that has been allowed to dry out may show yellowing leaves or shed its lower leaves. It is hence necessary to transplant your vine into a larger pot. One may want to transplant your plant into ground if it has grown too big. For plants grown inside a small pot, do increase the frequency of watering and apply a layer of compost on top of the soil surface to act as a mulch, which can help to retain water and reduce rate of evaporation.
The last question was about the growing of orchids. It is definitely not true that orchids do not require fertiliser. In fact, many species and hybrids need to be feed to grow healthily and produce flowers. Some fertilisers that are good for orchids include Gaviota (available from Far East Flora).
This orchid is an epiphyte and it is likely to be grown in a porous mixture such as charcoal chips and this dries out quite quickly. Depending on the growing conditions, it may be necessary to water it at least twice daily, especially it is grown under direct sunshine. The problem described by the reader seemed to suggest that his/her orchid plant may be suffering from heat and moisture stress. One can consider adding a little sphagnum moss around the root zone to help retain some moisture. It may be necessary to increase the frequency of watering too. Do also try to relocate the plant to a less windy area or provide some protection by putting up a barrier to wind by growing them amongst some plants.
Do check out the book published by the Orchid Society of South East Asia entitled ‘Orchid Growing in the Tropics’ for more information on how to grow various orchids in Singapore.