Pinwheel plant may be lacking in nutrients, water
I bought this pinwheel plant (right) six months ago and placed it near the balcony where there is strong afternoon sun and it is windy at times. Lately, the leaves turned yellow and the plant is no longer flowering. I water it daily in the morning and use an organic fertiliser every month. What is wrong?
Tan Geok Lin
There are several reasons for the issues you mentioned.
First, ensure your soil is friable and water-retentive. If it is compacted, you need to add good quality organic materials to help improve the soil structure and other soil properties, such asthe pH level, that are necessary for healthy root growth.
The yellow leaves could be caused by the lack of nutrients. Check the soil pH level to ensure that it is not too acidic or alkaline. The wrong soil pH will lock up nutrients.
You may want to consider using a complete fertiliser. Depending on the formulation, most organic fertilisers may not supply the full suite of nutrients needed for growth.
In a sunny location, plants transpire and lose water quickly. Soil that dries out regularly can cause leaves to turn yellow and older leaves to fall off. You have to increase the frequency of watering and water deeply. A layer of organic mulch around the roots will help to reduce the rate of evaporation.
Adenium plant seems to be infected
I have this white double-petal Adenium plant. But when it blooms, the flower turns brown (right). Why is this so? My red Adenium does not have a similar issue.
It appears that your white desert rose (Adenium obesum) is infected either by a fungus or bacteria.
Such infections occur when water touches the flower, causing it to be damaged and then infected by microbes that are present in the environment. Some cultivars are more prone to such damage and infection than others.
For now, remove the infected flower and discard it with your household trash.
Keep the plant under a clear plastic shelter so that it is protected from rain, but is still able to get direct sunlight that is necessary for healthy growth. Ensure that there is good air circulation so that moisture can quickly evaporate from the plant.
Consider using a fungicide spray to reduce the likelihood of the same problem recurring.
Ginger plants affected by changes in growing environment
My ornamental ginger plants have leaf burn (right) despite being in a semi-shaded open garden. How do I prevent this dried look? Can the red ginger flowers and rhizome be eaten?
Tan Geok Mui
The ornamental ginger is botanically known as Alpinia purpurata. It is commonly known as the red ginger, ostrich plume and pink cone ginger. It is a common landscape plant for tropical gardens.
Were your ginger plants recently planted?
Most of the time, new plants are propagated in a much shadier and humid environment of a production nursery. The growing of such plants in a new landscape that is drier and sunnier can lead to the burning of foliage as pictured.
Depending on the direction your garden faces, the shifting of the half-yearly direct sunlight exposure in Singapore can suddenly change the light intensity your plants are exposed to.
The burnt marks on the leaves could also be caused by chemical damage. Did you recently spray pesticides or fertilisers on your plants or were there works involving some chemicals being applied nearby recently? Chemical fumes can affect plants adversely.
You can prune the damaged leaves. With the right growing conditions, the plants should adapt and recover.
Also, check if the plants are regularly watered. The lack of water under sunny conditions can lead to plants being scorched.
You should also ensure that the soil is rich in organic matter - this can also help to retain water at the roots during hot weather.
Christmas tree may have unhealthy roots
My Christmas tree (right) is browning rapidly. What should I do?
Sagayamary Selvarani Das
The tree is likely the Chinese juniper (Juniperus chinensis).
Unfortunately, from the picture, the decline of the tree appears to be quite advanced and there is very little you can do to improve its health.
Check the health of the roots of the current tree if you intend to grow a new one in the near future.
The dying of Chinese juniper could be due to poor soil drainage. Soil that is compacted will not let water drain away and this can cause roots to suffocate and die. In turn, the tree will die.
Also, check if there are pests eating away the roots of the tree.
Termites can consume the roots and impede the uptake of water and nutrients that are necessary for growth.
Sky Fruit from a tree common in Singapore
I found this fruit (right) in my garden. What is it and is it edible?
The fruit is produced by a tree that is botanically known as Swietenia macrophylla. Its common name is Broad-leafed Mahogany, though it is known in Singapore as Sky Fruit tree.
Its fruit, which have hard rinds, grow towards the sky. This tree species can be found growing in parks and along the streets here.
Its seeds and extracts in the form of pills are sometimes sold in medical halls in Singapore.
The seeds' medicinal properties - such as its blood lipid-lowering properties - to date have been verified in animal models. Self-medication should be done under the guidance of a medical doctor.
• 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.
• Have a gardening query? E-mail it with clear, high-resolution pictures of at least 1MB, if any, and your full name to email@example.com
Plant talk and clinic
As part of the Singapore Garden Festival (SGF) 2018, to be held at Gardens by the Bay from July 21 to Aug 3, horticulturist Wilson Wong will give a talk on common garden pests and diseases, followed by a plant clinic at 6pm.
SGF ticket-holders can take along photos of their diseased plants to find out how to treat them.
BOOK IT / GARDENING MADE EASY: DEALING WITH COMMON PESTS AND DISEASES
WHERE: The Meadow, Gardens by the Bay, 18 Marina Gardens Drive
WHEN: July 22, 5pm (talk), 6pm (plant clinic)
ADMISSION: Free for SGF ticket-holders