Induce drought stress for plants to flower

My bougainvillea plants stopped flowering after I transferred them to the ground eight months ago. The area has direct sun for more than six hours a day and is regularly fertilised. How can I get my plants to flower again?

Jocelyn Lim

Bougainvillea plants flower when they are experiencing drought stress and exposed to full sun. The fence behind your plants may be blocking sunlight for at least part of the day. 

Your plants look to be dark green with soft stems. Ensure that you are using the right fertiliser, as a nitrogen-rich fertiliser will promote only foliage growth.

Also, regular watering or a moist location will not induce flowering.

As your plants are being grown outdoors, the larger soil volume will retain more water, which may mean that your plants may not be drying out fast enough with regular watering. Bougainvillea grown in a pot can dry out faster due to the limited soil volume.

Olive tree may have pest, root issues

My olive plant’s leaves seem dry, though some new ones are growing well. What are some common pests for this plant and what fertilisers should I use to get it to fruit?

Adrian Ling

As a woody perennial tree, olives may be infested by sap-sucking pests such as scale insects and spider mites. Regular checks for such pests are essential and early remedial action should be taken to manage the infestation. Good coverage with summer oil sprays is essential for effective pest management.

Olive trees grow slowly, so avoid heavy or regular feeding. Slow-release fertiliser pellets are usually sufficient. Overfeeding can lead to soft growth and issues with pests and diseases.

As the tree is of Mediterranean origin, grow it in well-draining soil to reduce the likelihood of root rot.

If your tree is on the older side, check the plant’s branches. When buying such specimens, the branches may have been pruned and their cut ends can decay quickly in Singapore’s humid climate.

Olive trees flower mainly in a low-temperature environment. In Singapore, they are grown mostly for their attractive silver foliage and interesting growth forms.

Tomato cultivars have different characteristics

Are these tomatoes unusual? My father claims not to have seen such tomatoes before in Singapore.

Heng Ching Kiang

These tomatoes are not uncommon, as similar types are sold in supermarkets. Numerous tomato cultivars exist that are suited for growing in different areas.

In Singapore, select humidity- and heat-tolerant cultivars that can produce fruit more reliably and are disease-resistant.

Avoid harvesting seeds from fruit bought from the supermarket, as the progeny generally do not breed true. Seeds of hybrids that possess certain desirable characteristics can be costly to procure, due to the extensive breeding and research needed to produce them.

Sweet potato plants need full sun to thrive

I cut and planted the sprout of a sweet potato. It has been six months and only leaves have grown. What is wrong?

Ng Ah Siang

Sweet potato plants photosynthesise and store food in underground tubers. A lack of light will lead to less food and smaller tubers.

It can be challenging to grow sweet potato plants in apartments, as the light levels are not sufficient for the growth of most sun-loving edible plants.

Your plant seems to have been pruned. Let it grow, as more leaves will generate higher photosynthetic activity.  A pruned plant will divert resources to the production of new growth.

You may want to raise the plant so the parapet wall does not shade it, but not so high that it can become killer litter.

Ensure your plant gets at least six hours a day of direct sunlight and try growing it in a deeper pot.

Finally, do not let all the nodes along the stems take root in the growing media, as this will promote the production of numerous small tubers along the stem, rather than several big tubers.

Guiana Chestnut needs to be moved to a larger pot

I have had this plant since 2020. Lately, its leaves have been looking smaller and less healthy, with brown patches on the stems. How can I save the plant?

Chua Li Lian

Judging by the lanky stems, your Guiana Chestnut (Pachira aquatica) is not getting enough sunlight. Make sure its location gets direct sunlight for at least six hours a day. 

Check if the roots of the plant have filled the pot. A pot-bound plant will dry out quickly. If this is the case, move it to a larger container. Water your plant regularly so it does not dry out, which causes lower leaves to turn yellow and fall. 

In a high-rise environment, plants may not dry out as quickly if their growing mix is rich in organic matter that retains moisture.

However, too wet a root zone can cause plant health issues, so use your finger to feel for moisture beneath the growing media surface. When it feels dry, water your plant thoroughly. If it feels moist, you can skip watering for another day or so.

You may want to make your own growing mix by incorporating more gritty components like fine expanded clay pellets or pumice for better drainage and aeration.

• Answers by Dr Wilson Wong, an NParks-certified practising horticulturist and parks manager. He is the founder of Green Culture Singapore and an adjunct assistant professor (Food Science & Technology) at the National University of Singapore.
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