Soil isopods are mostly harmless to plants
What are these insects? Are they harmful to my plant?
Jairus Wong
It appears that the creatures are terrestrial isopods.
The growing mix seems to be rich in organic matter. Isopods are generally harmless and feed on decaying plant material. They are important decomposers of organic matter in the soil ecosystem and help to improve soil nutrient content and quality.
They may occasionally become a nuisance when they feed on seedlings. As such, you may want to grow larger and more resilient plants in soil where you find isopods. Raise seedlings separately in new potting media away from these generally beneficial fauna in the garden.
Thai basil affected by downy mildew
My four Thai basil plants, which are grown in an open common ground plot that has ample sunlight, have yellow and dark stains on the leaves. What could be causing this problem?
Yeong Tze Way
The leaves appear to be affected by downy mildew. This disease tends to occur during rainy, downcast weather.
You may want to shield your plants from direct rainfall by setting up a clear plastic shelter. It is also vital to ensure there is air circulation. In addition, plants should be pruned and not grown too closely.
Applications of organic and preventive treatments such as lime sulphur or neem oil may help to reduce the incidence and severity of the disease.
Take cuttings to reduce cactus' height and keep it small
I have had this cactus - which was about 10cm tall when I got it - for 20 years. Recently, it has grown rapidly, perhaps because I repotted it twice. It now leans heavily to one side and continues to do so despite my staking it. What should I do? I am concerned it could break off if it gets too top-heavy.
Nick Cox
One way to solve the issue of a very tall and top-heavy cactus is to take tip cuttings and root them separately.
However, as there are many new growths, you can end up with a lot of plants. Once your cuttings have rooted, keep a few to grow and give the rest to friends and neighbours. The cuttings can also serve as a backup for the plant.
Another method is to repot your cactus into an even larger container. As the plant will continue to grow larger, you will need much stronger and lasting stakes - such as galvanised steel poles - that can be placed at several spots in the pot. You can then use wires to go around the poles at fixed intervals to help secure the cactus.
You can also use a stainless-steel wire mesh to go around the poles. Secure the mesh using cable ties which can be easily removed if you need to maintain the plant.
To reduce the weight of the cactus, prune some growth while keeping the form of the plant.
Corky Passionflower occurs as a weed
I found this creeping plant on my fence. Is its fruit edible?
Yap Hwee Pin
The vine is known as Passiflora suberosa. Its common names include Corky Passionflower and Corkystem Passionflower. This plant usually occurs as a weed in local landscapes and can produce leaves of differing shapes as it grows and matures.
Although it is a weed, it plays a key ecological role in urban landscapes. Its flowers provide nectar and its leaves are food for the caterpillars of butterflies such as the Tawny Coster, Gulf Fritillary, Julia Heliconian, Mexican Silverspot and Zebra Heliconian.
The fruit is usually not eaten.
Mickey Mouse Taro, Pink Dragon Alocasia are popular houseplants
What are these plants and how do I take care of them?
David Goh
The variegated plant on the left is a Xanthosoma sagittifolium cultivar known as Variegatum Monstrosum. Due to the shape of its leaves, it is commonly known as Mickey Mouse Taro. The other plant on the right with pink leaf stalks is an Alocasia cultivar called Pink Dragon.
Both are now very popular foliage houseplants.
If you live in an apartment, they grow best in a location which receives four to six hours of filtered sunlight a day. Good light is required to keep plants healthy and help them retain a compact growth form.
They need a well-drained growing mix and must be watered when they dry out. But avoid overwatering - a condition where the roots are perpetually wet - as that will cause the underground corm and crown to rot.
- Answers by Dr Wilson Wong, an NParks-certified practising horticulturist, parks manager and ISA-certified arborist. 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 stlife@sph.com.sg. We reserve the right to edit and reject questions.
