Root Awakening

Sawtooth coriander needs more light.
Sawtooth coriander needs more light. PHOTO: TERENCE TAY
White spots could be due to sucking pest damage.
White spots could be due to sucking pest damage.PHOTO: JOANNE CHIA
Chilli plant may be affected by mites.
Chilli plant may be affected by mites.PHOTO: WELVIN LIM
Fruit splitting may be due to hot and humid conditions.
Fruit splitting may be due to hot and humid conditions.PHOTO: L. TEO

Sawtooth coriander needs more light

I have tried many times to grow the sawtooth coriander, but it is not growing well despite getting water and indirect sunlight every day. How should I grow the plant?

Terence Tay

Your sawtooth coriander (botanical name: Eryngium foetidum) may be receiving insufficient light.

A plant that is not getting enough light will grow slowly and have thin and floppy leaves.

This plant is best grown under direct sunlight or filtered sunlight for at least six hours daily.

Under more intense sunlight, it should be kept well-hydrated. When it gets sufficient light, its leaves will become thicker and firmer. It will also grow more vigorously.

White spots could be due to sucking pest damage

I noticed tiny white spots on the leaves of my amaranth. What is the cause? Are the leaves still edible?

Joanne Chia

The numerous white spots could be due to damage by sucking pests, such as spider mites.

Turn a leaf over to check the type of pest infesting the plant. Spider mites can be very small and barely visible to the human eye.

Due to the regenerative growth capability of this plant, you can try to reduce the pest population by cutting off and discarding the infested parts.

Then spray the remaining plant parts thoroughly with less toxic pesticides such as summer oil solution to kill any remaining adults and young. Repeated applications are required to kill subsequent generations.

On a daily basis, you can also spray your plants with water to rinse off the pests.

The leaves are still edible after the pests have been washed off thoroughly. 

Calamansi plant may be infested by scale insects

My calamansi plant had small brown dots all over the leaves and branches. I scraped the dots off or removed the leaves. What else should I do?

Mahmuddin Abu Bakar

From your description, it appears that your plant may be infested by scale insects.

These pests have an armour which appears like a brown shell. They attach to the plant and suck sap from it and, over time, the plant may become weakened.

Scale insects can be scraped off easily by using your fingernail.

They can also first be gently removed from your plant with a soft toothbrush.

You can then spray a dilute solution of neem oil, summer oil or lime sulphur solution at least weekly to kill existing adults and young, to keep the pest population in check.

As these pesticides work via contact, you will have to ensure you cover all surfaces of the plant when spraying the solution.

Heavy rain will wash the pesticide off, so repeated applications are required to keep the pest population low.

Chilli plant may be affected by mites

What is happening to my chilli plant? The leaves are becoming deformed.

Welvin Lim

Your chilli plant (botanical name: Capsicum annuum) may be infested by broad mites.

Broad mites are a very common pest in chilli plants. They are microscopic in size and cannot be seen with the naked eye. The gardener knows of their presence only through the damage they inflict on plants.

The most obvious damage done by such mites will be the deformation of leaves. In very serious cases, new leaves curl up into a tight mass and the growing tip dies. Deformed leaves cannot be saved and the growth of the plant is halted.

Organic methods of controlling broad mites would include the application of sulphur soap solution (made by dissolving a sulphur bar soap in some hot water and then topping up with room temperature tap water) or lime sulphur insecticide that is sold at selected nurseries.

Regular applications are needed to manage the pest population and should be done during the cooler part of the day to avoid burning the leaves. A chemical pesticide known as abamectin can provide more lasting control.

Fruit splitting may be due to hot and humid conditions

My banana fruit split when they were not ripe. Why did this happen?

L. Teo

It has been documented that the skin of near mature or mature banana fruit may split due to exposure to an overly hot and humid environment while it is still on the mother plant.

During the fruit's growth and development, you may want to ensure the growing area is well-ventilated and that there is some shade to keep the developing fruit away from direct sunlight.

Harvest the fruit when it is mature but still green, and let it ripen in the cooler environment indoors to reduce the likelihood of its skin splitting. 

• 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. We reserve the right to edit and reject questions. Fruit splitting may be due to hot and humid conditions

A version of this article appeared in the print edition of The Straits Times on September 14, 2019, with the headline 'Root Awakening'. Print Edition | Subscribe