Root Awakening

PHOTO: LEON CHEE

Adenium has fungal disease

My two pots of adenium have many leaves with "burnt" patches (above right). The leaves are also not growing healthily on the short stems, which are drying up (above left). However, there are some leaves and flowers that seem unaffected. The plants get morning and afternoon sun and are grown on the balcony of my high-rise apartment. What is wrong with them?

Leon Chee

Your desert rose plants (botanical name - Adenium obesum) are likely to be infected by a fungal disease that is causing the leaves to be patchy and shoot tips to be dying back.

You can prunethe infected portions and apply some fungicide powder over the wounds.

Ensure that the plants are grown in direct sunlight and that the soil is well-drained.

You also need clean tools for pruning so that you do not spread diseases from plant to plant.

To minimise the incidence of a future infection, keep the plants sheltered during rainy weather and use a preventive fungicide.


New growths are stems of dragonfruit plant


PHOTO: MUI HUANG

Are the growths (above) that appear from the main stems the fruit of the plant?

Mui Huang

The growths are the new stems of the dragonfruit plant.

The fruit produced by the plant begins with the production of a very obvious single flower bud. The bud opens at night and reveals a large, white flower that is naturally pollinated by moths or bats.

Instead of allowing the stems to dangle in the air, it is best to grow the plant against a large and strong wooden structure, so that the stems will produce aerial roots that will cling onto the structure as it grows.


Caterpillars attacking Japanese sago palm


PHOTO: MABEL TAN

My plants (above) were growing beautifully, but recently started to wither badly. The new shoots withered in a week. What happened?

Mabel Tan

The plant is commonly known as the Japanese sago palm (botanical name - Cycas revoluta). The issue described is a common one where the emerging new leaves are damaged and die back. This is due to the feeding activity of caterpillars of the cycad blue butterfly.

Butterflies of this species lay eggs on new fronds and the caterpillars that hatch will feed on the young plant tissue, causing badly eaten leaves to often die back.

Japanese sago palms under such attacks repeatedly tend to decline over time as no new leaves are produced to support growth.

Insecticides like Dipel (based on Bacillus thuringiensis subsp. kurstaki), which work on just caterpillars, can be used as a preventive measure as soon as new leaves appear. They are effective if the caterpillars are very young but must be reapplied when it rains because the pesticide gets washed away.

Larger caterpillars can be removed by hand.


Coppertone Stonecrop needs more light


PHOTO: LIN MEIXIU

What is name of this plant (above) and how do I take care of it? Can it survive outdoors?

Lin Meixiu

The plant appears to be the Coppertone Stonecrop that is botanically known as Sedum nussbaumerianum.

It is one of the species commonly offered under the cacti and succulent section in nurseries and appears to be one that can be cultivated in Singapore under ambient conditions.

Your plant appears to be lacking in light - there are gaps between leaves and the entire plant is largely green.

If it is left outdoors, the plant is best grown under a transparent shelter to protect it from excessive rain.

It must be exposed to at least six hours of direct sunlight. Good light will ensure the plant adopts a more attractive, compact growth habit and the leaves will take on a bronzy colour.

The medium should be well-drained and made up of gritty materials like fine pumice or volcanic sand.


Fiddler fig plant's root system may be damaged


PHOTO: CHAN WEI CHUEN

I have a fiddler fig plant (above) that is dying. Its leaves are droopy and many are turning brown and brittle and curling at the edges. I thought the leaves were drying up because of insufficient water - I had watered the plant twice a week - so I increased the frequency of watering to every other day. But the plant continues to deteriorate. Now, one of its branches is completely bare because all the leaves have dropped off. The plant gets direct morning sunlight. Can it be saved?

Chan Wei Chuen

The symptoms appear to be related to the health of the roots.

An unhealthy root system will prevent the plant from taking up water. As a result, leaves and new growing tips will dry and die off.

You may want to carefully take the plant out of its pot to inspect its roots. Healthy roots should appear white and firm. Dead or rotting roots will be black or brown and mushy. Roots may also be infested by soil organisms like soil mealybugs.

Whether the plant can be saved depends on the state of its root system.

Ensure your flower pot has a drainage hole below. Water accumulated at the base of a pot with no drainage holes will drown roots and cause them to die.

Always check the moisture content of the soil before you water. You should water if the soil below the surface feels a little dry.

Do not allow a plant to dry out totally as roots will die and the affected plant will not be able to take up water.

• Answers by Dr Wilson Wong, an NParks-certified practising horticulturist and park manager. He is the founder of Green Culture Singapore and an adjunct assistant professor (Food Science & Technology) at the National University of Singapore.

• Have a gardening query? E-mail it with clear, high-resolution pictures of at least 1MB, if any, and your full name to stlife@sph.com.sg

A version of this article appeared in the print edition of The Straits Times on November 17, 2018, with the headline 'Root Awakening'. Print Edition | Subscribe