วันอาทิตย์ที่ 21 กันยายน พ.ศ. 2551

How to Grow Durians # 2

FROM FIRST PAGE OF DURIAN

Planting: In equatorial regions, the most favorable time for planting is winter from November through mid-January (and not during the February-May dry season). In tropical areas far from the equator, early spring is probably best but is likely not too critical.

In Malaysia, planting holes 0.6m [2 feet] in diameter and depth are dug and allowed to weather for 2-4 weeks. (The Brunei Department of Agriculture recommends .5 m deep by 1 meter in diameter.) Organic matter or compost at the rate of about 5-10 kg [10-20 pounds] is added to each hole, also about 200 gm [1/2 pound] of rock phosphate, and the young trees are planted with as little disturbance to the roots as possible. It’s advisable to go further than this, and add rock dust (which enhances a plant’s health and enriches the flavor of the plant’s resulting food harvest) as well as other available organic amendments, and use standard organic tree planting techniques.

In orchards, durian trees are commonly spaced 6-16 m [20 to 50 feet] apart, aiming for about 156 trees/hectare [64 trees/acre] to 40 trees/hectare [16 trees/acre]. T.S. Chang of Bao Sheng Durian Farm in Malaysia recommends 30 trees/hectare [12 trees/acre]. At closer spacings, thinning will be necessary by the time the trees are 8 to 10 years old to reduce tree density and give remaining trees room for further growth. As grafted trees may start bearing at age 4-6, planting the trees more closely in the orchard’s first decade is a way to increase fruit production from a given piece of land. However, T.S. advises against this, saying from experience that few growers who plant more closely can bring themselves to cut down any 10-year old bearing durian trees of good quality to thin out the orchard, and most often allow them to remain. In the long term, this is unfortunate for the trees and the grower, as the trees compete for canopy sunlight in the increasingly cramped situation and eventually grow very tall and thin with less fruitbearing capacity.

It's worth remembering that durian is a native of equatorial rainforests, eventually growing to the high canopy, and is at home amongst a mix of other plants and trees. As the Permaculture approach recommends, other useful plants can be grown among durian trees at ground level and lower levels. These can also provide needed shade during the durian trees' early life, as happens in the rainforest. The Brunei Department of Agriculture recommends interplanting durians with bananas and/or papayas.

young durian trees interplanted with bananas (Brunei Dept. of Agriculture photos)
The bananas or papayas should be planted 6 months ahead of the durians, at a spacing of 3 x 3 meters [~10 feet]. Eventually the durians will shade out the bananas or papayas, which can be trimmed and used as mulch and will also of course provide fruit harvest of their own. By the time the durians are fruiting, the banana or papaya plants should be removed, however, as their fruits will draw unwanted pest insects to the area. For trees that will remain interplanted among the durians indefinitely, in Malaysia, rambutan is a favored choice, as is nutmeg and chile pepper plants; but not mangos, mangosteen, citrus, starfruit, jackfruit, champedak, nor many others that can attract pest insects. The Brunei Department of Ag also suggests another alternative of interplanting with fast growing nitrogen-fixing-trees (there are a great many possibilities, including various species of Gliricidia, Sesbania, Leucaena, Albizia, Acacia, and others) which will provide shade, nutritious mulch, and soil improvement.

Propagation: Propagation of durian trees can be done through either seeds or by vegetative means.

Unlike most seeds of temperate-climate plants, the big seeds of the ultra-tropical durian tree have a very short period of viability out of the fruit, especially if exposed even briefly to sunlight: only a few days at most. (However, if kept in ordinary cool storage, they can be successfully be kept for a week, or as long as a month if surface-sterilized, placed in an airtight container and kept at 20º C. [68º F.]) This high perishability of durian seeds no doubt has been a factor in preventing the durian tree’s widespread dispersal far from its native territories.

The seeds are best planted or sprouted within a day or so from removal from the fruit, sprout end pointed down, to a depth of half the seed with the other half above the soil surface. Healthy durian seeds sprout as quickly and vigorously as bean seeds, usually within a few days but possibly as long as a week. For transport or mailing, the seeds are best immediately placed in moist coconut fiber.

Durian seedlings produce highly variable results. Their fruit may be better or worse than the parent tree, and it may be 10 to even 20 years before first fruit! ("It is reported that, in some countries, seedling durian trees have borne fruit at 5 years of age. In India, generally, they come into bearing 9 to 12 years after planting, but in South India they will not produce fruit until they are 13 to 21 years old. In Malaya, seedlings will bloom in 7 years; grafted trees in 4 years or earlier."—Julia Morton, Fruits of Warm Climates)

Therefore, vegetative propagation, which is not difficult, is universally preferred and recommended for reproducing cultivars with known desirable traits. A large number of grafting methods are commonly employed. In Malaysia, Indonesia and the Philippines wedge (cleft), whip, approach, Forkert, and bud grafting of durian trees are all common. Propagation by airlayers and cuttings does not work. Wedge grafting and bud grafting are probably the most common techniques. Click here to view the Brunei Department of Agriculture's durian-grafting instruction pages.

As reported by the authors of Tropical Tree Fruits for Australia (compiled by P.E. Page, Queensland Department of Primary Industries, Brisbane, 1984), growers in Thailand employ an unusual type of bottle graft with which many or most of their trees are grown. Durian seedlings that will serve as rootstocks are sown in beds and dug up when approximately 300 to 600 mm [1 to 2 feet tall]. The roots are packed with moist coconut husk fiber and sealed in a plastic bag. This rootstock seedling is then tied to a branch of the established durian tree that is desired to be reproduced, next to a lateral branch that appears suitable to serve a scion. The top of the young rootstock plant is then cut off, and the rootstock plant is inarched in a side-veneer graft to the branch/new scion. After the union is complete, the new scion is severed from the mother tree at about the level of the bottom of the seedling roots. The scion butt is also potted up and develops roots, so that the resulting grafted tree actually has two root systems, and is stronger and more vigorous as a result.

Most durian growers regard any variety of durian as suitable for a rootstock as long as it is healthy and vigorous. In Thailand, the common vigorous Chanee variety is said to serve very well as a rootstock. There is also increasing use there of some wild Durio species such as D. malaccensis, D. mansoni, and D. lowianus for resistance to Phythophora palmivora. In India, a relative of the durian, Cullenia excelsa (native to Sri Lanka) is favored as a good vigorous rootstock which is said to also hasten the time of first fruiting.

SEE PAGE DURIAN #1
SEE PAGE DURIAN # 3
SEE PAGE DURIAN #4

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