Orchid must be slowly acclimatised to higher light levels

I kept my orchid plant in the shade in my garden. It seldom blooms. Thinking this might be due to lack of sunshine, I moved it under the window awning where it gets the morning sun. However, its leaves developed white spots which then became bigger patches. Some also turned yellow. Did I do something wrong?

Shirley Toh

Plants grown in the shade should be introduced to more intense light in a gradual manner. Sudden exposure to intense light will cause the leaves to bleach and turn yellow. In more serious cases, burnt leaf tissues will also develop white patches. Such occurrences will not revert to their original form.

Try putting a shade cloth over the plant or moving it to a slightly shadier spot. Move the plant gradually to a brighter spot over a duration of several weeks. You will need to water your plant more often under sunnier conditions.

Allow stem-cutting to establish in the shade

I was repotting one of my Monstera deliciosa plants when the roots broke off. I immediately replanted the stem in the soil and packed it tightly around the base. How should I care for this plant? It was about to sprout a new leaf, but I am concerned that repotting has stunted its growth, as it no longer has roots with which to take up water.

Sam Yeo

First, avoid packing growing media around a stem-cutting too tightly, as this may cause poor aeration and drainage. This can impede root growth and lead to wet feet, which can kill the cutting.

To provide support for the stem-cutting, insert a bamboo stake into the growing media and tie the cutting to it. Use a growing mix for aroids and place the cutting in a bright, cool spot, away from draughts. Keep the growing medium moist.

If the leaves start to wilt, you can prune the larger ones in half and cover the cutting with a clear plastic bag with some holes cut into it. This can help to reduce moisture loss. Some hobbyists also root their cuttings in water. 

Once the cutting has produced sufficient roots, you can open the plastic bag gradually. At the same time, move the cutting slowly to a brighter spot. It will grow eventually.

Caterpillar attacks can be managed by applying Btk pesticide

How do I prevent caterpillars? They seem to breed even more during this time of the year. I tried using soap to get rid of them, but to no avail.

Adrian Ling

Caterpillar attacks can be prevented by physically enclosing your plants in a netted enclosure. You have to ensure the enclosure has no holes that allow butterflies and moths to fly into it to lay eggs.

An organic pesticide based on the bacteria called Bacillus thuringiensis subsp. kurstaki (Btk) can be used as a preventive measure against caterpillars. It is highly selective and should be sprayed on the plant’s leaves when an infestation is expected. This pesticide works best on young caterpillars.

Soap generally does not work on caterpillar attacks.

Pepper plant may be shedding leaves due to multiple reasons

My green pepper plant’s leaves fall off daily. What is wrong?

Teresa Fong Yoke Chan

The green pepper plant is a sun-loving plant and, in an apartment setting, should be placed in a location that gets four to six hours of direct sunlight daily. A lack of light can cause the leaves to fall and the plant will gradually decline.

A common pest that infests green pepper plants is the broad mite. This pest is microscopic and not visible to the naked eye. It attacks young developing leaves and causes them to appear distorted. Growing points can die due to a heavy infestation.

You can use diluted lime sulphur solution to manage a broad mite infestation. Regular applications are required to provide adequate control.

• 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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