Ask the Experts – Issue 21


Question I am hoping to seek some advice. I have grown some sunflowers from seeds since the beginning of this year. They grew rapidly initially but now they seem to have stopped growing at a height of about 45cm and they also look like they are not flowering. I add fertiliser (chicken manure from the nurseries) about once every two weeks. Any idea what could be wrong? - Wu Chun WeiAnswer: From the photos, it appears that the plants look malnourished and the pots are too small. Each pot should hold only one plant. A small pot means that the plants may not have received enough water and space for the roots to grow. Sunflowers require plentiful amounts of direct sunlight and regular fertilising – chicken manure may not be sufficient. You may supplement with inorganic soluble fertiliser or use bone meal instead, although it may smell – use a teaspoon per pot and water immediately. Sunflower roots also need a large space to grow and the soil needs to be kept moist. At the same time, given the amount of space in an apartment, sunflowers propagated in an apartment may not grow as large as those planted in outdoor plots. - Dr Wilson WongAsk the Expert team is made up of NParks horticultural and gardening experts. If you have any questions on plants or plant-related subjects, please send your question to Ask the Experts at

Total Comments: 2

Li-San 4/29/2014 1:37:43 PM

Hi W.L., Female fruit flies lay their eggs just beneath the skin of the developing fruit. Spraying the fruits with water-based permethrin solution would generally not be effective, as the pesticide is a contact insecticide, meaning it needs to be sprayed directly on the insects in order to kill them. The most environmentally friendly way of dealing with this problem is to protect the fruits from being infested. This would involve covering the fruits with fine netting or newspaper. However, this of course requires that it can be done safely and would be easier accomplished if the plant is a dwarf or of a small-growing variety. You could refer to this <a href="" title="webpage" rel="nofollow">webpage</a> and scroll to the section on making a fruit fly trap (Lynfield or bucket trap). You can replace the vinegar used in the webpage's suggested ingredients with fruit fly attracting solution available at major nurseries. Some people drop insecticide such as malathion into the solution to poison the fruit flies. You will often find that a variety of management methods have to be applied rather than just one solution in order to better control pest infestations.

W. L. ENG 4/21/2014 2:33:57 PM

Dear Dr Wilson Wong, I have a mango tree almost two storey in height. During the recent dry spell it flowers profusely. When the small fruits appear I spray it with a water based permethrin solution. Despite spraying 3 times over a period of three weeks the fruits which is mature now have worms inside. I have this worms inside the fruit from day one. How can I overcome this problem? Thanks and best regards W. L. ENG

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