Root Awakening: Premna bonsai needs to be well-watered and pruned gradually to improve growth

Premna Bonsai.
Premna Bonsai.PHOTO: HAN HWEE PING
Snails found on potted pencil pines.
Snails found on potted pencil pines.PHOTO: SOH KAI HAN
Caterpillar eating leaves of lime plant.
Caterpillar eating leaves of lime plant.PHOTO: SOH KAI HAN
Pomegranate plant.
Pomegranate plant.PHOTO: WILLIAM CHUA
Bittergourd.
Bittergourd.PHOTO: LEE CHEE CHEE
Lavender plant.
Lavender plant.PHOTO: LOIS LEK

Premna bonsai needs to be well-watered and pruned gradually to improve growth

I have a two-year-old bonsai tree. It has been shedding leaves and some branches are bare, but still continues to extend the branches which has leaves. Yet the leaves on the inner branches do not grow back. Should I prune the branches on the outside, which have leaves, to encourage the re-growth of leaves for the branches inside? But I am afraid the tree will become too bare.

Han Hwee Ping

The bonsai plant is likely a shrub that is botanically known as Premna microphylla. The leggy growth could be due to the lack of pruning or water that has caused the older leaves to fall off.

Bonsai plants are often grown in overly small pots to restrain growth. It is therefore recommended that you water the plants regularly to ensure they are adequately hydrated to prevent them from undergoing water stress, which can cause the leaves to fall.

You can attempt to prune the plant to encourage bushy growth. However, this has to be done in a gradual manner to retrain the plant to the desired growth form.

You should consult fellow local bonsai hobbyists for advice on how best to do this.

Finally, ensure your plant receives sufficient sunlight to ensure good health and promote vigour in the growth of your plant.

Use tea seed powder to contain snails and remove caterpillars by hand

A number of snails have been found on four of my potted pencil pines. Will they harm the plant? The snails have been removed and placed far away. How can I prevent them from returning? Also, caterpillars have been eating the leaves of the lime plant which I bought during Chinese New Year. Can they be left alone or should they be removed?

Soh Kai Han

Both snails and caterpillars can be removed by hand if there are not too many. This is the most environment-friendly and chemical-free way of eradication.

It is not recommended to use chemical-based metaldehyde snail baits to deal with snails in the garden as the baits are toxic.

You can use safer alternatives like tea seed powder or snail baits that are made from iron phosphate.

It is advisable to reduce the number of hiding places for snails in your garden. These are often dark and moist corners such as overturned flower pots and even patches of groundcover plants.

The caterpillar found on your lime plant is the larvae of the beautiful lime butterfly, which has specific host plants it feeds on.

You may want to pick and rear them in a tank where you feed them regularly in a more controlled manner with pesticide-free lime plant leaves. They can be released when they become butterflies as the adults are important pollinators for plants.

Alternatively, you may want to offer them to schools where teachers may be keen to rear them to let students learn about the life cycle of butterflies.

If the caterpillars bother you, pesticides such as Dipel (based on Bacillus thuringiensis subsp. kurstaki) or Spinosad can be used to manage them.

Pomegranate plant infested with mealy bugs

I have been using pesticides bought from supermarkets to remove the insects on my plants. I am not sure if they are mealy bugs. I cannot seem to remove them entirely and they keep reappearing.

William Chua

Your pomegranate plant (botanical name: Punica granatum) appears to be infested with mealy bugs, which are sucking pests that have a cottony coat. They can be difficult to eradicate.

You can first use a jet of water to wash them off the plant. Then spray oil-based pesticides such as neem oil or summer oil on the plant. These pesticides will coat remaining pests and suffocate them. Applications need to be repeated at least weekly or accordingly to the instructions on the label to keep the pest population low.

It is recommended you test the pesticide on a small part of the plant to ensure it does not burn the leaves before spraying it on the entire plant.

Ensure your plant is hydrated and spray the pesticide during the cooler part of the day. Complete coverage is needed for better control of the pest.

Well-pollinated bittergourd flowers lead to better fruit

I started growing bittergourds at home using seeds from a large bittergourd bought from the market. The plant grows well but the fruit are very small, although they taste nice. The fruit also turn yellow very fast. How can I improve the condition of the fruit?

Lee Chee Chee

Bittergourd fruits vary in size according to the cultivar. If the fruit are smaller than those you bought, here are some possible remedies.

Ensure the bittergourd flowers are well-pollinated. Bees are attracted to the yellow flowers and they are best at pollinating the flowers to ensure proper fruit development. When flowers are not pollinated properly, fruit can be small, develop abnormally or be aborted prematurely.

If bees are not visiting the flowers, you have to perform hand-pollination.

Bittergourd flowers are either male or female - only the latter produces fruit. You can use a soft paintbrush to harvest pollen from male blooms, which appear as flowers without an ovary behind the petals. Brush the pollen-laden paintbrush against the centre of a female bittergourd flower, which has an ovary behind the petals.

When the plant is fruiting, it is recommended that you feed it with a fertiliser that is high in phosphorus. Ensure the plant is well-hydrated at all times and do not let it dry out. You may find it useful to mulch the root zone of the plant with a layer of good-quality compost or shredded dried leaves to help conserve moisture and keep the roots cool.

Finally, wrap the fruit with newspaper to reduce attacks by fruit flies and caterpillars, which can lead to damaged fruit that will be aborted prematurely by the plant.

Grow lavender hydroponically in Singapore

Can this plant, which seems to be dying, be saved?

Lois Lek

The lavender plant (botanical name: Lavandula cultivar) cannot be saved as it has succumbed to disease.

Imported potted plants are often raised in cocopeat-based media, which holds too much moisture for growing in hot and humid Singapore. Such growing conditions often lead to fungal disease, which is very difficult to control.

Local gardening hobbyists have reported some success with growing lavender hydroponically. This can be done by taking healthy stem-cuttings and rooting them in water or in coarse gritty media like fine expanded clay pellets.

The rooted cuttings can be grown in a hydroponic nutrient solution and best results can be achieved by growing such plants under grow-lights indoors.

• 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.

A version of this article appeared in the print edition of The Straits Times on May 18, 2019, with the headline 'Root Awakening'. Print Edition | Subscribe