Blooms of Four O'Clock Flower open late

What are these plants on my balcony? One pot has yellow flowers while the other has purple ones. The flowers bloom in the evening and wilt the following day. How do I keep the flowers in bloom longer?

Robert James Tay

The plant is commonly known as Four O'Clock Flower. Its botanical name is Mirabilis jalapa. The short flowering duration is a characteristic of the plant and there is nothing much that can be done to prolong the lifespan of the blooms.

Its flowers, which are fragrant, usually open in the late afternoon and stay that way until the following morning before they fade. This makes them great flowers to enjoy after one has returned from work or the first thing in the morning.

Flowers of the plant may remain open all day when the weather is cloudy.

Periwinkle susceptible to stem or root rot

PHOTO: LIM LAI HUAT

I have grown many periwinkle plants, but they just wither and die each time. They do not have any disease and I water the plants every day. The flowers also get smaller even though I add fertiliser. What can I do?

Lim Lai Huat

The periwinkle plant (Catharanthus cultivar) is highly susceptible to stem or root rot, brought about by overwatering. Once a plant starts to wilt, there is nothing that can be done, except to discard it. For it to grow well, it needs to be in a sunny location with soil that is well-draining.

Avoid using a growing mix with too much organic matter and water when the mix feels dry.

Protect the plant during the rainy season and avoid growing plants too close to one another. Using a systemic fungicide such as propiconazole may help to prevent or reduce the incidence of stem or root rot.

Tip: Australian Clematis has white, fragrant flowers

The Australian Clematis - its botanical name is Clematis aristata - grows as a climbing vine. It produces white, strongly scented flowers.

It can be grown either in a container or in the ground and at a sunny location. Soil should be moisture-retentive and well drained.

The wiry stems with flowers can be cut and used in flower arrangements, but they will not last long. The plant is propagated via stem cuttings.

Lady's finger and chye sim infested by pests

My lady's finger plant seems to be infected with either insects or a disease. Meanwhile, my chye sim plant has white spots on its leaves. What do I do?

Lilian Ho

Your lady's finger has aphids, which are pests that suck sap from young, tender parts of the plant. They cause young developing leaves to become deformed.

For edible plants, you can use a strong jet of water to wash the pests off. For severe infestations, you may want to use organic pesticides such as summer oil or neem oil.

Follow the dosage recommendation of such pesticides.

Apply them when the weather is cool. The best timing would be either early in the morning or late evening.

Apply the pesticide several times to ensure current and subsequent pest populations are killed. You need to ensure the pesticide is sprayed on all parts of the plant, including the underside of leaves.

The silver markings on your chye sim - also known as Chinese Flowering Cabbage - are probably caused by small pests such as thrips.

You may use the same organic pesticides, but thrips are very difficult to eradicate with such pesticides.

It is best to remove badly infested plants and rotate the space to grow another unrelated plant or crop that is not a relative of the cabbage plant.

Lawson Cypress prefers temperate climes

I bought a Christmas tree last year. It turned brown despite getting sun and water. Can it be saved?

Jaimie Lim

The small decorative Christmas tree is botanically known as Chamaecyparis lawsoniana "Ellwoodii". Its common name is Lawson Cypress. It is often sold in a peat-based growing mix which holds an excessive amount of water. Plants often die of root rot due to prolonged wet feet.

You may want to reduce the watering frequency - do so only when the growing mix feels dry. The plant is from a temperate region and, in the long run, it may not grow well in the tropical climate of Singapore.

•Answers by Dr Wilson Wong, a certified practising horticulturist and founder of Green Culture Singapore (www.greenculturesg.com). He is also an NParks-certified park manager.

•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