Root Awakening: Prune Norfolk Island Pine to main trunk

Norfolk Island Pine.
Norfolk Island Pine.PHOTO: JENNIE YET
Guiana Chestnut.
Guiana Chestnut.PHOTO: BEN YEO
Japanese Yew.
Mealy bug infestation.
Mealy bug infestation.PHOTO: JOE LAU

Prune Norfolk Island Pine to main trunk

The leaves of this plant turned brown, so I pruned them. They do not seem to regrow near the spot anymore. The plant looks pathetic now. What should I do?

Jennie Yet

The plant you have is commonly known as the Norfolk Island Pine (Araucaria heterophylla).

It can grow into a large towering tree. Pruning the side branches will not lead to the growth of further branches at the cut end.

You should cut the entire branch all the way near to the main trunk.

The Norfolk Island Pine grows best under full sun. Shading of the lower branches can cause foliage to wither. Also, ensure the plant is well-watered during the dry period.

It is evident that your plant is grown in a pot where water supply at the root zone is limited. Drying out of the root zone in a container-grown plant can also cause the yellowing of foliage.

Guiana Chestnut may be suffering from wet feet

I have kept this plant indoors for more than a year. It was thriving, but the leaves recently started to turn yellow and dry up. I watered the plant twice every week with a cup of water each time. Is it underwatered or overwatered, or is the issue due to a lack of sunlight? I have a similar plant at the same location, grown under the same regimen and it is thriving.

Ben Yeo

The plant is commonly known as the Guiana Chestnut (Pachira aquatica). When grown indoors, it thrives on at least four to six hours of direct sunlight daily.

Note that the overhead ceiling lights do not give sufficient light intensity needed for its growth. You can rotate the plant to a sunny location outdoors for it to recuperate, perhaps during the weekends.

The soil should be well-drained and stay moist, not wet. Water the plant thoroughly each time and some excess water should come out of the drainage holes at the base of the pot.

The yellowing of leaves with the appearance of some brown mushy patches may indicate wet feet. Check the roots to ensure they are healthy. In wet soil, roots may die and turn mushy and brown. Healthy roots appear white and firm.

Soil in containers, depending on its composition, may be compacted over time, leading to poor drainage and drying. Soils that are rich in clay content will retain too much water. If there are some healthy roots left after inspection, pot the plant in a well-draining mix that is concocted for indoor plant growing.

Insufficient light for Japanese Yew

My beloved “pine” branch seems dead and I think it cannot be saved. What can I do to prevent the other branches from ending up the same way?

Richard Chua

The plant is botanically called Podocarpus macrophyllus and its common names include Buddhist Pine, Big-leaved Podocarp and Japanese Yew. There are several causes for the dieback of the branch observed. Ensure your plant receives sufficient sunlight. This plant grows best under full sun and the lowest branch seen could be shaded by the low parapet wall, which can cause the branch to die. Next, ensure the soil is welldrained. It should not be wet all the time and should dry out partially between each watering. Prolonged wet feet can lead to the death of roots and subsequent dieback of branches. Check the health of the bark and branch if you have cut it. Bark that falls off, and oozing and discolouration of the branch can indicate a disease. Cutting off the infected portion until healthy tissue emerges may be required and may be sufficient to manage the spread of the disease. Sterilise the cutting tool before you use it to prune other plants. If the disease progresses, there may be a need to send diseased plant part samples to a laboratory for a diagnosis and identification of the causative agent.

Treat mealy bug infestation with water

A white sticky substance is appearing on my plant. Should I spray insecticide regularly? What plant is it? It just grows out from the pot.

Joe Lau

The white sticky substance is a sign of a mealy bug infestation. These pests suck sap from the plant and weaken it over time. Small infestations can be removed by washing the pests off using a strong jet of water or by dabbing them with rubbing alcohol. For larger infestations, spray the plant thoroughly using summer oil, neem oil or a dilute solution of castile soap. These environment-friendly pesticides suffocate the mealy bugs and kill them. Good coverage and repeated applications are required to keep the pest population under control. More information, such as the type of flowers, is needed before the plant can be properly identified.

Buy pH meters from aquarium shops

I learnt that pH 6 to 7 is best for plants to flower or bear fruit. Where can I buy a pH tester/meter to measure the pH level of soil? I have asked around nurseries, but was told they do not stock it.

Cynthia Yap

Soil pH is a measure of the acidity or basicity of soil and the numbers you mentioned cover the range that the nutrients needed for growth, development and reproduction are most available to plants. There are several types of pH meters that can be used to measure soil pH.

You can buy an instrument called a battery-operated pH probe or pH pen, which is available for sale in most aquarium shops or hydroponic suppliers. Get a meter you can do calibration with standard solutions as well as with the automatic temperature compensation function.

To use such an instrument, you need to mix one part of the soil sample you want to test with 21/2 parts of distilled water. Stir thoroughly and let it stand for about one hour. You can use the pH probe to measure the pH value of the resulting suspension.

• 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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A version of this article appeared in the print edition of The Straits Times on June 08, 2019, with the headline 'Root Awakening'. Print Edition | Subscribe