Root Awakening


Haze may lead to leaves yellowing

When the haze worsened, I noticed that the leaves of my plants such as the chilli and cherry tomato ones (right) turned yellow. This happened even though I gave them more water.

Jasmine P'ng

Different plants respond differently to the haze. The most obvious effect is that less light is available as pollutants scatter sunlight.

Plants need sunlight for photosynthesis and both the chilli and tomato plants need direct sunlight to thrive.

Some plants may also be sensitive to the higher-than-normal level of pollutants in the air during the hazy period.


Stress from either one or a combination of these two factors - there may also be other environmental factors - might have caused the leaves to turn yellow.

The plants will not lack water if a sufficient amount is given and the root zone is kept moist most of the time.

Tip: Pink Trumpet Vine a good climber


The Pink Trumpet Vine, botanically known as Podranea ricasoliana, is a free-flowering plant that produces bunches of attractive pink flowers.

Often sold as a shrub in pots, it can grow as a climber on a garden structure, such as a trellis.

Best grown outdoors where it can get direct sunlight and lots of space, the Pink Trumpet Vine prefers fertile, well-draining soils. Prune this plant periodically to promote new growth and induce vigour.

Pandan may be affected by spider mites

My potted pandan grows well, but there appears to be a layer of white substance on the leaves. Why does this happen?

Sim Hwee Keng


The symptoms could be due to a spider mite infestation. Spider mites appear as tiny red dots which are barely visible. Check the underside of leaves to see if this is the case.

When there is a spider mite infestation, you should examine if the growing area is suited for cultivating the affected plant.

In a high-rise environment, the air can be too dry and windy to grow pandan, which prefers a protected and moist location.

Also ensure that it is exposed to sufficient sunlight that is vital for healthy growth. It is important to correct the growing conditions as a healthier plant will be more resistant to pest attacks.

Loss of bonsai leaves due to changing conditions

I bought this bonsai a few months ago. Over time, it started shedding leaves badly. I water it daily and keep it on the ledge of a window. Why does this happen?

K.W. Fong

The response shown by your bonsai could be due to two factors. First, there could have been a sudden change in growing conditions.

Many bonsai are woody shrubs that require direct sunlight to grow well. They are often grown in open areas in a nursery. The shift from outdoors to indoors, which is a change in growing conditions, can cause the plant to become stressed and lose its leaves.

Depending on the species, some plants will recover and produce new leaves. They can acclimatise to growing indoors gradually, provided they are exposed to several hours of direct sunlight daily.

Another reason could be due to lack of water. Note that bonsai plants are grown in constrained pots with very little soil volume. The soil holds water for use by the plant between each watering cycle.

Stress caused by the lack of water for prolonged periods can lead to leaf loss. It is important to ensure that your bonsai is watered regularly. Keep the root zone moist at all times.

Screen frangipani from strong winds

My frangipani plants do not grow many leaves. When it rains heavily or the winds are strong, many of the green leaves drop off. What should I do to get more luscious growth?

Yip Chui Lim


As the leaves of the frangipani are easily stripped off from your plant whenever there are strong winds, it is vital to provide protection for it.

You can put up a screen or grow a row of plants, such as a hedge, around the more exposed areas of your garden. However, do note that the frangipani is sun-loving and such measures should not cast too much shade.

Another alternative would be to move your plant to a place in the garden where it is less windy.

To promote foliage growth, a balanced fertiliser can be used to feed your plant. But avoid over- fertilising with such a fertiliser as there will be more foliage at the expense of flowers.

  • Answers by Dr Wilson Wong, a certified practising horticulturist and founder of Green Culture Singapore ( He is also an NParks-certified park manager.
  • Got a gardening query? E-mail it with clear, high-resolution pictures, if any, of at least 1MB and your full name to
A version of this article appeared in the print edition of The Straits Times on December 05, 2015, with the headline 'Root Awakening'. Subscribe