Dear Plant Doctor
Q
HOW long does it take for a longan tree to bear fruits? Mine is three years old and all it does is sprout big, huge healthy leaves that I prune away constantly. I also fertilise it fortnightly. – Ellis Lee
A
YOUR tree should be flowering and bearing fruits at this age. However, longan is a subtropical tree that prefers slightly cooler temperatures than those we experience in Malaysia. This means growing fruit-bearing longan trees here can be a challenge, and quite a lot of technical expertise is required to induce flowering and also to maintain the tree.
However, one simple problem with yours might be too much fertiliser. Feeding it once every two weeks is too often. Generally, longan trees require about 500g to 2kg of NPK (nitrogen, phosphorus and kalium) 15:15:15 fertiliser per tree per year, split into four to five applications over the year.
Q
I HAVE been growing this lemon tree for about four years now, and it barely has lemons on it. There are many little black dots on the leaves that can’t be sprayed off; I tried to trim them off but they keep coming back. Today, I saw two small lemons dropped prematurely. Please help! – Betty
A
THE black spots could be signs of aphid attacks. These aren’t usually a problem unless you see many infected leaves. You can spray neem oil mixed with water to control aphids.
Premature fruit drops or no fruits could be a sign of over-watering or over-fertilisation. Water just enough to keep the top soil moist (not wet). And fertilise according to the instructions on your fertiliser package; get those specially formulated for citrus trees for easier maintenance.
Q
I HAVE these plants which look like they are about to wilt (right); is it because of too much or too little water? Also, what’s the ratio of neem oil to water for making an insect repellant? And where can I buy neem water? I added orange peels into my compost and maggots appeared. How do I eliminate them? – Sally
A
UNDER- and over-watering often cause the same symptoms. Stick a finger into the soil, about 2cm to 3cm deep, and feel if the soil is too dry or wet. If it is too dry, you need to add more water; if too wet, stop watering until the top soil has dried. If possible, change the soil if you have over-watered.
The ratio of neem oil to water is about 10ml of neem oil to 1 litre of water. You can easily get neem oil online.
If your compost has maggots, it means the heap is not composting well. Proper composting should not have any bad smells or maggots. You may have either over-watered your compost heap or added the wrong mixture/combination of browns and greens.
Avoid adding meat or oil into your compost heap. Alternatively, try burying your orange peels so they are not exposed to flies.