Lemon balm stressed by excessive light
I bought a pot of lemon balm from a supermarket, transferred it to a bigger pot and topped it up with a mix of sandy, loamy soil. It was growing well for a few months, but started to wither after I trimmed it a little. The pot is placed on my patio's wall which faces the west. It also receives little rain. What happened?
Koh Soh Ling
Your plant appears to be stressed by excessive exposure to direct sunlight. It could possibly lack water, too, as the leaves have become small and brittle. Some have also turned brown.
You may want to move your plant to a cool location where it gets filtered sunlight instead. The root zone should be kept moist and not allowed to dry out excessively.
The plant should also be protected from excessive wind that can dry out the plant.
Tip: Air plant with trailing growth habit
Many people are familiar with air plants, which are largely epiphytic plants belonging to the genus Tillandsia. An interesting species to look out for is Tillandsia ionantha var. vanhyningii.
Unlike many cultivars of Tillandsia ionantha, which grows as a tight rosette, this variety has a trailing growth habit. New growing points continuously emerge. Over time, and under optimal growing conditions, a sizeable clump can be obtained.
When plants are about to flower, the leaves surrounding the emerging flowers take on a pretty pink blush. Tillandsia ionantha var. vanhyningii can grow under filtered or direct sunlight. It requires a humid environment with good circulation to thrive.
Pinch off tips of petunia to spur growth
I bought two of these petunia plants during Chinese New Year and transplanted them into a long container. They have been flowering non-stop and the stalks continue to grow, with lots of flowers and buds. But the upper leaves are starting to turn yellow. The plants get the sun from 2 to 6pm. Is it good to add fertiliser when the plants are flowering? What should I do to ensure the lower buds grow and blossom too?
You may want to pinch off the growing tip of your petunia plants to encourage them to become bushier. The removal of the growing tip can encourage side shoots to emerge from the base of the plant. These will grow and, in time, produce more flowers.
Spent flowers should be promptly removed to discourage plants from producing fruit and seeds.
If the upper leaves turn yellow, the plants may lack fertiliser. Use a water-soluble fertiliser such as Phostrogen.
Remember to first use a more diluted version than recommended on the product label to avoid burning your plants.
Simpoh Air's leaves used to wrap food
I saw this beautiful plant blooming with two kinds of flowers at Upper Peirce Reservoir. Is it possible for a plant to bear more than one kind of flower?
The plant is commonly called Simpoh Air (its botanical name is Dillenia suffruticosa). The yellow structure is its flower. The other part is its ripe fruit which has split open to reveal the seeds that are covered in a red aril - either a covering or an appendage of some seeds.
Its fruit face upwards, while the flowers face down. It is a native plant of Singapore and, in the past, its leaves were used to wrap food such as tempeh, a fermented soya bean cake.
Maniltoa tree also known as Handkerchief Tree
I saw this unusual tree in my neighbourhood. Are the white things hanging from the tree flowers? What is the name of the tree?
It is likely a species of Maniltoa. It could be Maniltoa browneoides, which is commonly known as Dove Tree or Handkerchief Tree.
Widely grown as an ornamental tree, the white portions seen at the top of the tree's branches are new emerging leaves which hang down, making them look like handkerchiefs hanging on the tree.
• Answers by Dr Wilson Wong, a certified practising horticulturist and founder of Green Culture Singapore (www.greenculturesg.com). He is also an NParks-certified park manager. He will speak about growing succulents, starting a miniature garden and more at the Singapore Garden Festival next month. General admission ticket to the festival applies (go to www.singaporegardenfestival.com).
• Have a gardening query? E-mail it with clear, high-resolution pictures of at least 1MB, if any, and your full name to firstname.lastname@example.org