Root Awakening


Calla lily thrives in cool climate

I just bought this pretty plant (above) from the nursery. What is it and how do I care for it?

Larry Cheng

The plant is called the Calla lily (botanical name - Zantedeschia hybrid). It has an underground rootstock and is often grown at cooler, higher altitudes.

For it to thrive, the temperature at night needs to be much cooler than that in the day.

Like many deciduous plants, the Calla lily also generally requires a rest period and resumes growth only when growing conditions become conducive again.

As such, it would tend to be a difficult plant to grow well in tropical Singapore and is best treated as a temporary display plant here under ambient conditions.

Desert rose best grown in a sunny spot


I got this plant (above) about a month ago. It has many buds, but before they can bloom, they dry up, turn black and fall off when touched. What is the cause of this? The plant gets ample light and is watered regularly.

Mariah Ng

The plant is likely the desert rose (botanical name - Adenium obesum). The premature dropping of flower buds can be caused by a sudden change in growing conditions.

Is your plant grown in an area that is very windy? Constant winds can dry flower buds out and cause them to fall.

If the new location it is now in is suitable, the plant will adapt and recover and normal growth will resume soon.

Note that the desert rose needs a sunny location with at least four hours of direct sunlight to thrive and flower. A well-drained soil mix is required to grow this drought-tolerant plant.

Lack of sunlight, coupled with a wet root zone, can lead to a lack of flowers, lanky growth and possibly stem and root rot issues.

Pine trees need more light


What is wrong with my pine trees (above)? They turn brown from the bottom. I have treated them with pesticide.

Marga Tan

The plants are likely the Blue Point cultivar of the Juniperus chinensis and are commonly known as Blue Point Juniper.

From your picture, the growing location appears to be shaded on one side by a wall, and this could be the cause of the decline of the plants.

The damaged foliage will not recover, unfortunately. This species needsa sunny location to grow well.

Also, the plants need dry bases and are best grown in well-drained soil. If your soil is overly clayey, it can retain too much moisture at the roots, making the plants prone to disease.

Finally, always check if your plants are sensitive to chemicals you are applying on the leaves. This can be done by applying the chemical on a small part of the plant and checking for adverse reaction.

If there is none, you can then apply it on the entire plant.

ZZ plant may need new potting soil


What is wrong with my plant (above)? Why are the tips of the leaves yellow and are they burnt? The plant is grown under a covered car porch.

Catherine Kuek

The plant is the ZZ plant (botanical name - Zamioculcas zamiifolia).

How long has the plant been growing in its current pot and soil mix? If it is in an old soil mix, the problem could be a plant nutrient issue.

Potted soil that has been used to grow a plant for a long time can be exhausted of certain nutrients. Also, nutrients that have not been used may have built up to toxic levels. The symptoms on the leaves appear to show the effects of both.

To ascertain the exact cause, you need to do a soil test and look at the health of the roots.

If old soil is indeed the issue, you can remove the old potting mix from the roots. Trim unhealthy roots - these usually appear hollow or black and mushy - and pot the plant with fresh potting mix. Keep it in a cool location with filtered sunlight until it recovers from the transplanting procedure.

Over time, the plant should produce healthy growth.

Butterfly pea flower plant has nutrient deficiency, fungal disease


There are brown patches on my butterfly pea flower plant (above). The leaves are also yellowing. These plants are about six months old and were grown from seeds. They are in a planter box under a partially sheltered roof area. They are still creeping upwards, but do not look healthy. How can I restore their health?

Ong Yang Ming

The yellowing of the leaves of your blue pea plant (botanical name - Clitoria ternatea) is a symptom of a nutrient deficiency, where the plant is not able to uptake essential nutrients required for healthy growth.

Often, it could be an issue where the plant is growing in soil that is of the wrong pH (acidity/alkalinity) range, where nutrients get locked up and become unavailable.

To ascertain this, you need to perform a soil pH level assessment. If the soil pH level is indeed in the wrong range, you will need to adjust the pH level up or down, using garden lime or sulphur respectively.

Also, check that you have been fertilising your plant regularly with a complete fertiliser.

The soil for your plant should have organic matter and be well-drained, friable and aerated.

Soil conditions that are not conducive for healthy root growth will also lead to nutrient uptake issues.

The brown spots on the leaves appear to be a symptom of a fungal disease. Remove and discard the infected leaves. You may want to apply a contact chemical fungicide such as captan to reduce the incidence of the disease.

Ensure the plant has optimal nutrition and is grown in an area where it is well ventilated and gets at least six hours of direct sunlight. Such growing conditions are required so the plant is healthy and robust to ward off infections.

• 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

A version of this article appeared in the print edition of The Straits Times on November 03, 2018, with the headline 'Root Awakening'. Print Edition | Subscribe