Set of leaves likely from grafted rootstock
I bought this kaffir plant when it was growing in a small pot. Now, it has grown into a bigger plant. However, why are there two types of patterns on the leaves? Some parts of the leaves also have spots. Will this plant bear fruit?
The kaffir lime (botanical name: Citrus hystrix), also known as limau purut locally, is easily recognisable via its two-lobed leaves that look like the numeral eight.
This citrus is often sold as a grafted plant as it is too slow-growing from seeds and cuttings are very difficult to cultivate.
The leaves that do not look like those of the kaffir lime are likely produced by the rootstock, which was used to graft the kaffir lime.
Trace the branch to where it originated - it should be near the base of the plant. You will also see the graft union above it.
In this case, you can cut off the unwanted branch as its growth is usually more vigorous and can take over the kaffir lime plant over time.
Ensure your plant is grown under direct sunlight as it will not be healthy when grown under semi-shade or in an area where sunlight is not sufficient.
Plants fruit only when they have reached a certain size - around 1m or more - so ensure the pot is large enough to support the plant's growth.
The leaf spots are not so visible in the picture, so it is difficult to make a diagnosis.
The slightly distorted leaves are likely caused by sucking insects that fed on the sap on the developing leaves, causing them to deform. This is evidenced by the sooty mould seen in some leaves and is produced by the sweet excretion from sucking insects.
A common sucking insect pest often seen on citrus plants is the scale insect. You can manage it by spraying plants with summer oil.
Flowering shrub is the Sweet Osmanthus
I bought this plant about 10 years ago and was told it produces a sweet-smelling flower. But I have not seen the flower yet. The plant has been green all this time. What plant is it?
The shrub is likely the Sweet Osmanthus, which is commonly known by the Chinese as "gui hua". Its botanical name is Osmanthus fragrans. Its flowers are used to infuse black or green tea to make a scented beverage. They can also be used to make a jellied dessert.
The shrub produces very small flowers which can be easily missed. Although the plant can grow in tropical Singapore, it needs cooler conditions to produce flowers.
As such, it is not uncommon to see this plant producing flowers, although only in small numbers, during the cooler period of the year, which is usually at the end of the year in Singapore.
Dracaena is infested by scale insects
What is causing this condition in the plant and how do I cure it?
The plant appears to be a species of Dracaena. It seems that your plant is being infested with scale insects, which are sucking pests. The infestation looks severe and is a common occurrence of a plant grown in a shaded spot.
You can either prune and discard badly infested portions or use a soft toothbrush to remove the scale insects.
After removal, spray the plant thoroughly and regularly using organic pesticides such as neem oil or summer oil, both of which kill the scale insects by suffocating them. Repeated application of the pesticide is usually required to keep the population low enough to not weaken the plant.
Do move your plant to a sunnier location if it has been situated in shade.
Wilting rosemary may be lacking in or having too much water
Why are the leaves of my rosemary drooping and turning brown? Could it be due to too much direct sunlight or a lack of water?
There are two main reasons when a plant is wilting. The most common is due to the lack of water. If your rosemary plant is healthy but just lacking in water, it should revive after it has been given water.
Look at the root ball - if it is very light and dry, you can sit it in a shallow dish of water. After an hour or so, the root ball would have absorbed some water and must be promptly removed to avoid suffocating the roots.
If a plant is left in a dry state for too long, its roots can die by drying out. It is important to then ascertain how long it takes for a pot of moistened growing media to dry out slightly so that a watering regimen can be devised. Water should then be given soon after.
Another reason a plant wilts is due to overwatering.
In the case of the rosemary - often sold as a plant grown in a water-retentive growing mix locally - it wilts as a result of its roots dying due to prolonged wetness, which suffocates and kills the roots, leading to the inability of the plant to uptake water.
Disease due to pathogenic fungi or bacteria can subsequently set in and eventually kill the plant.
Check chrysanthemum for sucking pests and protect plant from downpours
What are the conditions required for chrysanthemums to grow well? The tips of the buds of my plant have been turning black. The plant is currently placed outdoors and gets afternoon sun. There are also a lot of ants in the flowers.
Soh Kai Han
Chrysanthemums, in general, require a cooler environment and good light to thrive.
They should be grown in a sunny spot with at least four hours of direct sunlight.
This plant is a short-day plant. To promote profuse blooming, you may need to shorten the daylight exposure by covering the plant with a light-proof box. It should receive less than 12 hours of daylight.
The blackening of the flower buds could be due to a number of reasons.
Heavy rain in the tropics falling on the plant can cause injury and secondary infection in the damaged plant tissue. Such portions should be pruned to reduce the spread of the disease.
In Singapore's tropical weather, it is recommended you protect the plant from heavy downpours - this can be done by sheltering the plant with a clear plastic sheet which allows light to pass through.
Ants may be attracted to the flowers due to the nectar in them, if any.
However, do inspect plants for sucking pests such as aphids, which produce sugar-rich honeydew.
If there are such pests, they can be washed off using a strong jet of water.
If the infestation is severe, you may want to spray the plant with either an oil-based pesticide such as summer oil or neem oil, or a pyrethrum-based pesticide.
• 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.
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