BITTERGOURD PLANT INFECTED WITH DISEASE

I noticed tiny yellow spots on the leaves of my bittergourd plant. Are these pests or do they indicate the plant is lacking nutrients? If so, what nutrients should I feed it?

Rita Tong

The yellow spots could be fungal disease brought about by shady or rainy conditions.

Ensure your plant is grown under direct sunlight - the lack of light can cause plants to weaken and become prone to disease.

A dense and shaded canopy will be conducive for disease-causing organisms to thrive and infect a weaker plant.

Also, give your plant ample air circulation so that the leaves are dry.

Rainy conditions can bring about disease due to rain damage as well as prevailing moist conditions with the lack of sunlight.

As such, it is best to grow your crop during the drier part of the year to reduce the incidence of disease.

You can prune the leaves with yellow spots. There is no need to feed the plant nutrients.

MING ARALIA CAN BE PROPAGATED BY STEM CUTTINGS

I received this plant about 11/2 years ago. It was between 7cm and 10cm then, but has grown to about 1m now and looks like a Christmas tree. Can I cut the stem to regrow it?

Meranda Chia

The plant is one of the many cultivars of Polyscias fruticosa, commonly known as the Ming Aralia.

With the Christmas festive season around the corner, why not give it some support by propping it up with a bamboo pole and adorning it with lights and decorations?

If this plant has grown too tall, you can cut it down.

The resultant cut stem can be portioned into 10cm lengths. These can be planted in smaller pots for them to root and they will grow into new plants.

The Ming Aralia can grow both under direct and filtered sunlight. It is also a resilient plant to grow in the home garden.

LIME PLANTS NEED SUNLIGHT, WELL-DRAINED SOIL TO THRIVE

I usually get lime plants after the Chinese New Year festive season. However, to get them to continue flowering and fruiting is a chore. What is lacking in the plants ? Do I prune them after every fruiting? Also, what is the name of the big lime plant? The leaves and fruit also keep dropping.

Lynne Teo

The lime plants appear to be in poor health.

Do note that such plants do best under direct sunlight for at least six hours a day. If the plants are growing in a shady corner, they tend to lose vigour and decline gradually.

The soil should be well-drained as citruses, in general, do not like wet feet.

Check if the growing medium is still suitable for the plants. Over time, depending on the composition, some growing medium breaks and settles down. This leads to a growing mix that has compacted and can hold too much water.

You can take the plants out and carefully remove the outer layer of the spent medium, then pot them with a well-drained mix that has more gritty materials.

Fruit dropping could be due to plant stress brought about by excessive or too little water as well as infestation by fruit flies. There is usually no need to prune the plant after fruiting.

As for the big lime plant's identity, it could be a cultivar of lime (Citrus × microcarpa).

The exact identification can be tricky as there are many cultivars and many look similar.

FUKIEN TEA TREE IS A POPULAR BONSAI CANDIDATE

This plant has been growing in my flower pot. I had pruned the grown branches, but it keeps growing. What kind of plant is it and is it safe to keep it?

Sarojani Rethnavelu

It is commonly known as the Fukien tea tree. Its botanical name is Ehretia microphylla. Locally, this plant is widely used as a bonsai candidate where it is trained to become a miniature tree in an artistic form.

You may find it growing spontaneously in your garden beds or flower pots, as its seeds are likely to be dispersed by birds that consume its small red fruits.

It grows best under direct sun, but can also tolerate filtered sunlight. Its leaves are reportedly used in tea-making and have medicinal uses too. Its red fruits are said to be edible.

SOURSOP TREE LACKS NUTRIENTS

My soursop tree is about 3 1/2 years old. Some six months ago, the leaves turned yellowish-green and new branches stopped growing. But it has lots of flowers, although none developed into fruit. I used to prune the plant regularly to use the leaves for making tea and new branches would grow after a few weeks.

Lim Joo Joon

The soursop tree is showing generalised yellowing, which indicates that it may be lacking nitrogen. Have you been fertilising the tree?

It is not clear, from the picture, how your plant is grown.

Check that it is not grown in compacted and poor-draining soil in the ground. Compacted soil can be remedied over time with mulching and forking of the surface soil, but do take care not to damage the roots.

Waterlogged conditions can be difficult to correct if the plant is growing in low-lying ground. Also, soursop trees do not transplant well. In this case, you may want to start new plants and grow them in a more suitable location.

If the plant is grown in a pot, its roots may have filled the container and nutrients may have been exhausted. It may also experience water stress easily due to a small soil volume. Consider moving the plant into a larger container or grow it in the ground.

•Answers by Dr Wilson Wong, an NParks-certified practising horticulturist, parks manager and ISA-certified arborist. 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.