Sow seeds of desert rose in well-drained mix; tomatoes not suited to Singapore climate

There are many seeds in a pod of my desert rose. How can I plant them? Also, the fruit from my tomato plant are small. Why is this so? Can you help identify the variety?

James Mary Nancy

For your desert rose, it is advisable to use a thin wire to wind around the seed pot. Next, use a fine mesh to make a net to enclose the fruit of the plant - this will help catch the seeds when the fruit mature and split open. Germination rate is high only with fresh seeds.

The seeds of the desert rose plant have a cottony fluff. Some people remove the fluff before sowing them.

Use a light and well-drained mix when you sow the seeds. They should not be buried deeply - use enough soil to just barely cover them.

The soilhas to be kept moist and the seedlings that emerge later have to be moved to a bright location to prevent them from etiolating (stretching of stems due to the lack of light).

Some tomato cultivars, especially the larger fruited ones, prefer a cooler climate to thrive and develop properly.

In tropical Singapore, it is recommended to cultivate cherry tomato varieties as these produce fruit here more reliably.

Grow Chinese thuja in containers to manage size

My neighbour gave me these miniature trees before she moved. If I were to transplant them to my garden plot, will they eventually grow into big trees?

Sheena Goh

The plant is commonly called the Chinese thuja or Oriental arborvitae and its botanical name is Platycladus orientalis. It is a slow-growing species and can grow into a tree several metres tall.

This plant dislikes wet feet and shade, and should be grown in a sunny location with well-drained soil.

If soil drainage is an issue, try growing it in a large container. Its size can also be managed more effectively if it is grown inside a container.

Hibiscus in need of iron

My hibiscus used to grow well and flower regularly. A month ago, the leaves started to curl, their edges turned yellow and new leaves grew smaller. The plant, which is exposed to full sunlight, has also stopped blooming. What is wrong with it?

Anna Tan

Your hibiscus appears to be suffering from a very severe case of iron deficiency. The yellowing, called chlorosis, starts with the young leaves, leaving the veins still green.

Common cases for iron deficiency are alkaline soil and soil that is not well-drained. You need to check the pH level of your soil using a soil pH test kit.

Alkaline soil can be corrected - although the process can be slow - by adding sulphur to the soil. Good quality organic matter can also be added to help improve drainage and aeration for healthy roots.

At the same time, you can look for water-soluble fertilisers that have chelated iron for easier absorption by your hibiscus.

Mites causing stippled leaves

I have pests on my plant and have started spraying white, clear oil on it a couple of times last week. Does that help and how long should I keep spraying the oil before I can see results? I live in an apartment and the plant is grown on my balcony and receives ample sunlight.

Soh Kian Peng

From the stippled and distorted appearance of the leaves, it appears that your plant is affected by mites.

Mites suck sap from leaf tissues, leaving small yellow dots. Also, some types of mites, such as the broad mite, are very small and invisible to the naked eye. The damage they cause is the distortion of new leaves.

Petroleum-based products are generally effective in containing the pest population.

You may want to rotate this with a sulphur soap solution, made by grating a sulphur soap bar and dissolving one teaspoon of soap flakes in a small quantity of hot water. This is then topped up to 1 litre with tap water. Shake the solution well before spraying it on the plant.

When using sulphur soap, test it on a small part of the plant before spraying the entire plant to see if there are adverse reactions. This should be done during the cooler part of the day.

Ensure that the plant, including the new growing tips, is thoroughly covered with the solution. Repeated applications are required to manage the mite population.

Spider plants need more light

I have two spider plants that had been growing quite well, but have recently looked sickly. The new shoots turned brown almost at the same time as they appeared. What is wrong with the plants? I water them daily and they are placed on a shaded balcony with less than an hour of morning sun.

Cheong Yin Ping

Spider plants (Chlorophytum comosum) are often sold as indoor plants, which is misleading. In fact, they require at least four hours of filtered sunlight daily to grow well. The lack of sunlight will lead to weak plants that are susceptible to pest and diseases.

In your case, the lack of sunlight coupled with moist conditions render your plants susceptible to fungal or bacterial infection that exhibits as rot of the new leaves.

You can prune infected leaves and move the plants to a brighter location for them to recuperate.

It is advisable to cut down on watering for now to reduce the spread of the disease. However, do not allow the plants to dry out excessively as that will do more harm than good.

• 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

• 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.