Overly wet soil may be cause of falling blooms

The flowers on my desert rose fall after 10 days. What should I do?

Sharon Lim Lay Choo

The dropping blooms of the desert rose (Adenium hybrid) may be due to a number of reasons.

During rainy season, heavy rain in an exposed area can damage flowers and cause them to drop prematurely, so consider moving the plant to a sheltered area. Excessive water in the root zone can also cause opened flowers and buds to be aborted.

The desert rose is sun-loving and it should get as much direct sunlight as possible. The growing media should be well-drained and allowed to dry out a little before watering again.

Grow stem-cuttings of lavender in new soil, rid chilli plant of white flies

My lavendula is drying up and its stems are turning brown. I bought and re-potted it with organic compost mix three weeks ago and grew it in planters facing north. What is wrong with it? Also, the leaves of my chilli plant have white spots . Are they harmful and how can I remove the spots? Are they the reason my chilli plant is scrawny? Finally, is my HDB garden overcrowded? My friends have said I am overcrowding my plants, which are mostly herbs.

Helen Cheong

In hot and humid Singapore, the issue with your lavender plant is a common one. Often, imported potted lavenders are grown in a water-retentive, cocopeat-based mix and the overly wet root zone will lead to root rot disease. Once manifested, the disease cannot be treated.

What you can do is take stem-cuttings of the plant and grow them in a better-drained soil mix containing good quality, gritty burnt earth, compost and fine expanded clay pellets.

Some dolomite can be added when the plants are established to make the root zone more alkaline.

Lavender needs to be grown in a sunny location. Water it only when the soil mix starts to dry out.

The chilli plant is affected by white flies. The spots are a stage in the life cycle of white flies.

You can use summer oil, neem oil or soap solution to spray the plant. Ensure all surfaces are covered and repeat the application to make sure the pest population is kept at a low level. Follow the instructions on the label to dilute pesticides and also observe the withholding period, which refers to the time that needs to elapse before you can harvest the plant.

Your garden does look crowded. The second row of plants further from the grille may not get sufficient sunlight. Most herbs require at least four hours of direct sunlight to thrive. The lack of sunlight will lead to weak and lanky plants that are prone to pests and diseases.

Fruit of fragrant shrub not usually eaten

What is the name of this plant and is its fruit edible?

Mui Huang

The plant is commonly known as Dwarf Murraya or Orange Jasmine. Its botanical name is Murraya paniculata "Min-A-Min" and the plant is a recent introduction to Singapore. Often sold as a shrub, it can grow into a small tree over time. It prefers a sunny spot with well-drained soil.

This cultivar is more floriferous compared with the regular Murraya paniculata. It produces bunches of fragrant white flowers. The fruit is usually not eaten.

Prune diseased leaves to prevent spread of infection

I got this orchid two months ago. Initially, I noticed small crawling bugs in the pot when I watered the plant and used bio-pesticides and neem oil to try and get rid of them. But the young leaves are turning spotty black. Will this condition spread to other plants?

Kor Soi Wei

The orchid is from the genus Epidendrum. If you live in an apartment, grow it in a spot where it can get direct sunlight for at least four hours daily. It is an epiphytic orchid that likes a porous media and, in Singapore, it is often potted using charcoal chunks. Feed it with a water-soluble orchid fertiliser to promote growth.

I cannot identify the bugs without a picture. You can try getting rid of them by soaking the pot in a pail of water for a short time. The plant should not be left in water for too long to avoid suffocating the roots.

The leaf lesions could be caused by infection of a bacteria or fungus. A bacterial disease will often manifest as a water-soaked, mushy lesion. Prune affected parts to prevent the spread of the infection.

If it is a fungal infection, a fungicide application may be necessary.

Handle your orchid well as damage caused by rough handling can injure leaves, leading to infections. Ensure the plant is also grown in a well-ventilated area.

Hand pollinate to help chiku tree fruit

We have had a chiku tree for 23 years and it bore only a couple of tiny fruits. Why is this so?

Sebastian Sim

To grow your chiku well, ensure that it is in a sunny and well-drained location. The soil around the root zone should not be overly compacted and a layer of leaf litter or good quality compost should be applied at all times to increase the vigour of your tree.

It is reported that the flowers of the chiku are not compatible if they come from the same tree. You may need to plant another tree to allow cross-pollination to occur to increase fruit production. Avoid using pesticides excessively as this will decrease the population of pollinators that help to transfer pollen between flowers. Consider hand-pollinating your plant if pollinators are absent.

•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