Root Awakening (18 Jun 2011)

This is the the last instalment of the Root Awakening column for the month of June 2011. Answers to two questions were provided.

The first question was about why the leaves of a frangipani showed signs of drying up. This could be a sign of a mealy bug infestation. One may want to check the undersides of the leaves for an infestation of mealy bugs which suck sap from leaf tissues. They appear as white cottony masses that congregate along the mid-rib and veins of leaves. Leaves that have been attacked often become warped and deformed and they finally dry up and fall off. Control the population of such sucking pests by spraying the underside of leaves with white summer oil (organic) or any other pesticide that is indicated for treatment of mealy bug infestations. You may want to remove and discard badly infested leaves before spraying to reduce the amount of pests to be dealt with.

Another point to add is to check for infection by the rust fungus. Severely infected leaves will eventually dry up and fall off. One should make an effort to remove all infected leaves as the spores from infected leaves will go into the soil and infect other frangipani plants.

The second question was about curling and yellowing of the leaves, as well as, deformation of flowers seen in the hibiscus plant. The symptoms described may be indicating that the plant is lacking in certain mineral nutrients. To correct the problem, one may want to feed plants with a water-soluble fertiliser that contains chelated elements. Look at the ingredient list on the fertiliser’s label. The correction of a severe deficiency may take many months. The symptoms of any minor element deficiency show up on the new growth with the new and younger leaves being affected. When the deficiency is corrected, the new growth will be normal in appearance.

Note that even with a good feeding programme, nutrient deficiencies can still occur due to changes in soil acidity, organic content and drainage. As Singapore’s soil is often clayey and compacted, it is beneficial to improve the quality of soil by the addition of organic material such as good quality compost. Compost is valued for its soil conditioning value. Incorporate compost into the top few inches of soil to improve its properties.

One more point to add is to check also for mealy bug infestations in the leaves. Infestations by sucking insects will also cause leaves to become deformed.

Heliconia wilsonii in Flower

Heliconia wilsonii, an uncommon species that naturally grows in Costa Rica and Panama, has finally flowered in Singapore after about three years. Grown from seeds, this plant could have flowered earlier as it was transplanted from an outdoor location a year ago into a container where it has been growing for about a year.

Its inflorescence, from a far, looked like those produced by Heliconia psittacorum cultivars. The bracts are bright red in colour while the true flowers inside are bright yellow in colour – what a perfect contrast of tropical colours!

This is the first time it flowered and it is not certain whether it will be floriferous under local conditions. There is limited information about this plant and the only profile can be found in the book ‘Heliconia – An Identification Guide’ by Berry and Kress. Internet resources are very scarce and an online herbarium resource (Las Cruces Herbarium Collection) at the time of writing this entry featured specimens collected in localities with highland altitudes above 1000 m. This may suggest a shy flowering habit of this heliconia in lowland, tropical Singapore. Hence it may grow but flower less often here.

The plant is grown under partial shade conditions with well-draining soil. Currently, it measures about 1 m in height and grows as a tight clump with a distinctive cannoid growth habit. Not particularly fast-growing, it will surely make a less invasive and much welcomed mid-ground to foreground heliconia species for outdoor tropical landscapes, provided it flowers often enough locally.

Root Awakening (11 Jun 2011)

Here’s the Root Awakening column for the second week of Jun 2011 and answers to two gardening questions were given.

The first question was about the ability to grow plants in a lift landing in a HDB apartment block. Unfortunately, there are not many plants that will thrive under the dimly lit conditions commonly encountered. Note that the ceiling fluorescent lights that are turned on at night in HDB corridors are usually not intense enough to support plant growth.

Many plants will deteriorate after some time after being located in such a condition. If it is possible, do a rotation between groups of plants to be displayed in your lift landing. After being displayed for a week or two in the dim lift landing, you can shift them to a brighter place to recuperate. Note that many sun-loving plants will quickly deteriorate when they are placed in the shade, even for short durations.

To grow a plant successfully in a given location would depend on its light requirements. Its leaves need to be exposed to the light rays of either filtered sunlight or direct sunlight for at least for 4 hours daily, as a general rule of thumb. For most apartment dwellers this would involve putting the plants just next to the parapet and raised from the floor so that they can be exposed to sunlight that streams through into the growing area.

The second question was about the existence of anti-mosquito plants. My answer is no. There is no plant that will repel mosquitoes on its own. The range of plants that are reported to possess mosquito-repelling properties do so only after the leaves have been picked and crushed to release the essential oils.

DIY Floating Gardens in HortPark

If you drop by HortPark recently and took notice of the Water Garden located in front of the Visitor Center, you would have seen the floating gardens that have been set afloat on the water surface.

These floating gardens are a practical solution so that aquatic plants can still be displayed as the pond currently has a hard bottom with an undergravel filtration system installed at its base. There is neither an appropriate substrate at base nor containers can be put in to grow and display aquatic plants.

Each floating garden is created using readily available materials (see schematic diagram for details of construction). The floatation device took us a quite some time to source. It comprises a slab of extruded polystyrene board which is usually used for insulation of roofs. Unlike widely available white polystyrene boards used in art and craft, this board is made of dense polystyrene is more buoyant, resistant to wear and tear under the elements and does not absorb significant amount of water.

A selection of aquatic marginal plants, which naturally grow in waterlogged soils along a pond’s edge, with different growth forms, foliage textures and colours, is creatively combined to plant up these gardens that magically hover on the water surface. Of particular note is the use of North American Pitcher Plants (Sarracenia), which are colourful, insectivorous plants that grow in sunny and boggy sites in their native habitat.

Besides being decorative, floating gardens, in general, draw excess nutrients from the water column, especially if you feed your fish frequently. Fish waste that is produced in excess can lead to algae blooms. On a larger scale, such set-ups perform phyto-remediation work, where plants help to purify water in reservoirs, lakes and rivers.

Floating gardens also promote biodiversity. They provide shelter for fish and other aquatic organisms from the sun and predators. Dragonflies and damselflies are given a place to perch on and water birds can even roost in them if they are large enough!

Root Awakening (4 Jun 2011)

Here’s the Root Awakening column for this week where two gardening questions were given answers.

The first question dealth with the identities of two commonly encountered shrubs which are great hedge plants. One of them is Syzygium campanulatum and there are two cultivars available currently. One has orangey new leaves whilst another has maroon new leaves. Both the orange and maroon cultivars have become quite popular shrubs for landscaping in Sinagpore. They are best grown in a sunny, well draining spot to ensure the leaves put forth their vibrant colour. Some people prune the shrub regularly to promote new colourful foliage growth.

Another hedge plant identified was Baphia nitida. It is an ‘old school’ plant that has been around for quite some time and is fondly remembered for its use to screen away rubbish points in public housing estates in the past. It is a highly versatile shrub as it also thrives in shady areas.

Both shrubs are easy to grow and relatively fuss-free. But Syzygium campanulatum may occasionally get attacked by caterpillars or beetles.

The second question was about the effect of putting ice cubes on the root zone of a bamboo plant with the hope that the leaves will be greener. As far as I am aware, there is no scientific evidence to support such a claim. Excessive chilling of roots can do more harm than good. Yellowing bamboo leaves can be brought about by a variety of reasons, such as by the lack of certain nutrients, and it is best to find out the root cause and remedy it.

Persicaria capitata – A Groundcover for Medicinal Gardens

Persicaria capitata is a medicinal plant known via a range of common names which include Pink Knotweed, Japanese Knotweed, Himalayan Smartweed and Pink Bubble Persicaria. A member of the Polygonaceae family, this plant used to be known botanically as Polygonum capitatum but now has been reclassified into a new genus, Persicaria.

A native of Asia, this plant has naturalised in various parts of the world and has become an invasive weed in areas where the climate permits. It is an herbaceous plant that adopts a prostrate growth habit, meaning it creeps near the surface of the plant. Owing to this growth habit, Persicaria capitata is often grown as a groundcover plant.

A candidate for medicinal gardens, it is a highly ornamental plant suited for planting in the foreground in a landscape. For example, it can cleverly be grown between some rocks. The leaves of Persicaria capitata are green in colour and the chevron that adorns each leaf becomes more obvious under direct sunlight. The reddish stems contrast against strongly the foliage. Flowers of this plant are produced freely in the form of small pink globes that are held well above the foliage. This plant emits a strong odour when parts of it are crushed.

Persicaria capitata is a perennial plant in Singapore which prefers to be grown under direct sunlight and a moist, well-draining location. It seems to be able to grow in poor, clayey soils and can be drought-tolerant when established. Under optimal growing conditions, it is able to form a dense mat of foliage that hugs the ground. It is relatively pest- and disease-free under local conditions and can be easy to propagate it via stem-cuttings. Note that it is important to plant Persicaria capitata in a weed-free area as it has been noted that grassy weeds can still grow through a dense mat of this plant and eradication of these unsightly weeds can be very difficult to perform.

Persicaria capitata is used in Traditional Chinese Medicine where its aerial parts are used to brew a tea which is consumed for the treatment of a range of urological disorders, such as kidney stones and urinary tract infections. An in-vitro study reported that traditional use of this plant for the treatment of urinary tract infections can be attributed to the presence of anti-bacterial and anti-inflammatory agents found in the plant. Persicaria capitata has also been found to contain antioxidants.

Passiflora foetida – A Weed with many Roles & Uses

Passiflora foetida is a member of the Passion Fruit family, Passifloraceae. It could have been a native of South America but has since naturalized in most tropical countries, including Singapore. Unlike its relatives, namely, the Giant Granadilla (Passiflora quadrangularis) and the Common Passion Fruit (Passiflora edulis), Passiflora foetida occurs mainly as a weed and it is getting uncommon nowadays as Singapore continues to urbanise. A number of varieties of this plant are known to exist.

Its common names include the Stinking Passion Vine or Wild Water Lemon. Its species name ‘foetida’ has the meaning of “stinking” in Latin which refers to the strong odour that is emitted by damaged foliage. Note that the stems and leaves of this vine are toxic and suspected to have caused poisoning in livestock. Interestingly, the young shoot tips and leaves are also valuable, wild-gathered vegetables in several South East Asian countries where they are thoroughly cooked by boiling first and then consumed in a soup. Leaves have medicinal properties where they are used to treat neurasthenia, insomnia, early menstruation, edema, itching and coughs.

The plant itself, is a vine, like other Passiflora species. The stems of this plant are thin and wiry and covered with numerous sticky hairs. They are herbaceous when young and gradually turn woody with age. Its leaves are three- to five-lobed and hairy to touch too. The flowers of this plant are quite attractive but small in size, about 5 cm in diameter. Flowers are usually white in colour with a purplish center.

The fruits of this species are quite interesting as they are encased with leafy sepals that are finely dissected. Each fruit is about 2 to 3 cm in diameter and they turn from green to orange when ripe. There are varieties which produce fruits that turn red when ripe. The fruits do not split open when ripe. Note that the young fruit is cyanogenic and hence poisonous. They are only edible when ripe and children in rural villages in Singapore decades ago would be able to recall the fun of popping the yellow/orange ripe fruits into their mouths as they play along in the kampong. Each fruit has numerous black seeds embedded in the whitish, sweet pulp where seeds dispersed by birds.

Passiflora foetida is considered as a protocarnivorous plant. When the vine flowers, the leafy sepals that encase the flower are reported to produce sticky, dew-like secretions at the tip ends and these may help the plant to trap insects. There is insufficient evidence to show whether or not, the plant gains any form of nourishment from trapped prey.

This Passiflora species mainly occurs as a weed, sometimes invasive, in wet areas although it can tolerate drought when established. It is common in plantations, rough pastures, roadsides and wasteland. It is a ‘useful’ weed which is sometimes used as a soil cover in plantations to control lalang (Imperata cylindrica) and soil erosion.

It also plays an important ecological role. The young leaves and shoots of Passiflora foetida are consumed by caterpillars of the Leopard Lacewing (Cethosia cyane) and Tawny Coaster (Acraea terpsicore) found locally in Singapore.