Monday, January 22, 2007

Correction on burnt soil

The bags of burnt soil sold in KL for RM 1.20 per bag actually contain about 5.3 kg of burnt soil, not 3 kg as earlier reported.

Because of the wood-ash mixed into it, burnt soil contains a useful level of potassium, one of the essential elements for plant growth. The word potassium itself is derived from 'pot ash'.

Friday, January 19, 2007

Gardening on tropical clay soil

Clay soils in the tropics are not the ideal medium for plant growth, because clay particles stick together to impede penetration of water and air. On lawns, clay soils get compacted with time, starving the grass roots of oxygen.

Where plants have been growing naturally for a long time, leaves, bark, roots and other plant parts decompose and make the top layer of soil porous. Such top soil is the most fertile of natural soils, but it takes a very long time for new topsoil to form.

Chinese gardeners discovered long ago that the underlying clay soil, if burnt over a wood fire, becomes porous, friable and non-sticky, allowing for excellent water and air penetration. We do not know who discovered the process. For a description, we have R.E. Holttum's account in his book, Gardening in the Lowlands of Malaya, first published in 1953. Holttum was Director of the Singapore Botanic Gardens and Professor of Botany at the University of Malaya.

"The earth is broken up into fairly large pieces, and piled up on top of some old wood and other refuse, into a heap some four feet deep and six feet or more across. A cover to keep off rain is necessary. The stacking of the pile is of course a matter requiring skill. It must allow just enough circulation of air to keep a slow fire burning. The fire is allowed to burn for two days or sometimes more. When the operation is finished, the earth is changed from its original condition of clay to a porous granular state. It will consist of a fair propertion of large pieces, which should not be broken up too small, grading down to dust. The dust is not good for plants that require a particularly well aerated soil, and can be removed if necessary by the use of a fine sieve. The essential properties of the burnt earth are that it will absorb water without becoming sticky, that the lumps do not readily break down when the soil is watered; and that it is sterilized, all pests and diseases and harmful micro-organisms being destroyed. "

Yesterday, I visited a place in Sungei Buloh, just outside Kuala Lumpur, which produces burnt soil. There were about 10 kilns on the site, on leveled ground cut out from a hill side. Each kiln is a square enclosure with sides about 6 ft long. A post is erected at each corner, to support a roof of galvanized iron sheets ('zinc sheets') 6 ft or 7 ft above the ground. Planks are nailed to form walls on three sides. The fourth side is left open for stacking the wood and soil. First, wooden billets are closely stacked on the floor, to form a layer one foot thick, with some gaps for ventilation. Then lumps of clay soil, cut out from the exposed hillside, are laid on top of the wood to form a 2 ft layer. Then another layer of wood is laid on top, followed by another layer of clay. Then the roof is fixed, and the fire is lit. The fire burns for one week, and the pile takes another four days to cool down. The burnt soil, mixed with wood ash, is then passed through a sieve, the purpose of which is to hold back the larger lumps that need breaking down. There is no attempt to remove fine dust.

Burnt soil is used extensive in and around Kuala Lumpur and retails at $1.20 per bag of about 3 kg. At the kilns, it is sold for 80 cents a bag. In Ipoh, 3 hours drive away, it is sold for $2.00. Burnt soil is also produced locally in Ipoh but is said to be of lower quality. The difference, apparently, is that the clay soil in Sungei Buloh contains a good proportion of sand, which makes the particles more friable.

Thursday, January 18, 2007

Identity of Bauhinia kockiana in doubt

Two experienced gardeners, one in Kuching and the other in Singapore, have told me that the name Bauhinia kockiana seems to have been applied to two different species. If there has been a mixup of identities, the only way to sort them out would be to compare the two plants against scientifically authenticated specimens in a herbarium.

The plant illustrated and described in Tropical Horticulture and Gardening is the one that is commonly grown in Malaysia and Singapore, but it only came into the market in the 1990s. It has become very popular because it flowers practically throughout the year.

The other plant is rare but seems to have come into cultivation much earlier. In Singapore, it flowers profusely once a year.

Wednesday, January 17, 2007

Citrus microcarpa on sale early

The first Citrus microcarpa plants are now on sale in Kuala Lumpur at MR 38 - MR 48 for plants about 1 m tall, heavily laden with fruits. Whatever technique they use to stimulate heavy fruit production, it certainly works, for this species as well as for the kumquat, Citrus japonica. The latter has oblong fruits while the former has round fruits. Unfortunately, the fruits are already yellowing and softening, and Chinese New Year is one month away. The timing is off, at least for this batch of plants.

Thursday, January 11, 2007

Chinese New Year and Citrus fruits

The mandarin orange, Citrus reticulata, is in greatest demand during the Chinese New Year when they are served to guests and given away as presents. This custom is particularly strong among ethnic Chinese in Malaysia and Singapore. Mandarin oranges are imported from China. They grow in Malaysia but fruit irregularly and local fruits are considered inferior. In China, they fruit at the right time. Since the date for the Chinese New Year follows the lunar calendar and is out of synch with the solar calendar, and since plant behaviour is believed to follow the solar calendar, I have never understood how mandarin oranges in China 'know' when it is time to ripen.

Another Citrus associated with Chinese New Year in Malaysia and Singapore is the locally grown Citrus microcarpa (known as limau kasturi in Malay and calamondin in the Philippines). The plants flower and fruits irregularly throughout the year, but nurserymen have learnt to manage them so that they flower before the festival and fruits ripen just at the right time. The plants, heavily laden with fruits, are used to as decorations. Most years, the growers get the timing right, but this year is disastrous. I hear that the price for plants has doubled compared to last year because of very poor fruiting. This is blamed on the exceptionally wet weather. It has been raining every day for over a month and there has been serious flooding in many parts of the region.

I have a plant that is growing vigorously in my garden, flowering and fruiting profusely and totally unaffected by the wet weather. It grows in a pot of horticultural carbon. All the excess water simply drains off. Improved drainage may be what the plants need most in wet weather.