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.
Management:
Following planting, young durian
trees should be provided with temporary shade and complete wind
protection for the first year, as in a shadecloth nursery structure or
equivalent. The structure of the young trees and their leaves is such
that strong winds can twist the leaves right off, a setback from which
they are unlikely to ever fully recover.
Proper pruning of the durian tree is said to be
important to obtain a tree form that encourages early flowering and
good yields. The pruning system commonly used in Southeast Asia
includes:
-
formative pruning resulting in a main
leader; after about age 2 or 3 the interior is thinned out, removing
all thin or dead branches and water shoots
-
encouraging early branching to
encourage early bearing
-
topping to maintain a manageable
tree height as the tree grows older
-
general maintenance pruning
contributing to a healthy and productive tree, removing dead,
broken or diseased branches and water shoots, and allowing free
circulation of air and plenty of sunlight throughout the canopy
In Southeast Asia, cut surfaces are routinely
treated with a fungicide and bitumastic compound (use an organic
equivalent).
Durian growers in Thailand are often advised to
keep the area under the tree and drip line area free of weeds, manure,
and mulch, primarily so as to not create a microclimate suitable for
the thriving of Phythophora palmivora disease. (As previously
mentioned, it is not clear if this is necessary or advisable in using
strictly organic methods. Durian trees are otherwise
benefited from manure and mulch, like many other trees). Likewise, for
the same purpose, the trunk of the tree is kept free of any water
shoots and weak branches up to a height of about 1 m [3 feet] above
the ground. However, tropical legume cover crops between trees, such
as perennial peanut, are recommended.
Durian trees are surface feeders, and if any
weeding is necessary (with a cover crop like perennial peanut, there
shouldn’t be much), care should be taken to prevent damage to the
roots.
Durian trees remove a relatively low amount of
nutrients from the soil. However, like many other fruit trees, it is a
good idea to at least quarterly topdress the soil under the tree with
a mix of organic fertilizers (preferably particularly rich in nitrogen
and potassium) during the first five years. (Animal manures are favored in most places for this
purpose, but not in Thailand, where chemical fertilizers are widely
used in commercial production). T.S. Chang of Bao Sheng Durian Farm
recommends placing topdressed fertilizer just beyond the edge of the
root zone so that the trees’ roots will chase after it and expand
their reach in the process. The times a few months before flowering,
during fruit development, and after harvesting are favored for
fertilizing durian trees throughout Southeast Asia.
Water: In Asia, areas with a dry season longer
than 3 months are regarded as marginal for durian, unless adequately
irrigated, in which case there is no problem. Micro-sprinkler or drip
irrigation can be used. Durian trees are as incapable of withstanding
any standing water around their trunks as papayas; they will simply
die. In low-lying rainy areas, it may be advisable to construct
surface drainage systems to prevent that possibility from ever
occurring, or to plant only on sloped land, as is done in many areas
of Southeast Asia.
The times most critical for water for the durian
tree are during flowering and fruiting. In equatorial regions, it needs at least three to
four weeks of dry weather without rain to produce flowers to fill all
branches. (Farther from the equator as in Hawai`i, this may not hold
true, and day length and temperature may be the primary factors in
inducing flowering). Like mango trees, heavy rains and wind during flowering can
knock off many of the blossoms, decreasing or even eliminating fruit
production that season. When blossoms are forming, water is sometimes
deliberately withheld to enhance flowering. To maximize flower and
fruit production, after allowing a 3 to 4 week dry period, growers in
Malaysia then begin applying irrigation. Topdressing the trees with
organic fertilizer just before flowering also increases production.
Various cultivars may have their own unique responses to dry weather
and irrigation; for exam-ple, the common Malaysian cultivar D24 is
sensitive even to short dry spells; the common Thai variety Chanee tends to drop flowers if watered as much as other
varieties. An unseasonal drought may provoke durian trees to an
out-of-season round of flowering and fruiting.
Pests: As with any plant or tree, the best way
to minimize damage of durian trees or fruit by pests or disease is to
keep the soil and tree as maximumly healthy as possible using modern
organic methods.
Except for usually light damage by local fruit
borers, beetles, and leaf cutters in some areas, the tree and fruit
tend to be relatively free of insect pests. Phytophthora palmivora is
a dreaded fungus disease of durian trees in Southeast Asia. The
organism is a primary parasite of durian roots. Symptoms are canker
development on the trunk at or just above ground level, and an oozing
of brownish-red gum at the collar of the tree, up the trunk and down
to the roots, which can result in complete girdling and subsequent
death of the tree. The organism gains access to the interior tissues
of the tree suitable for its growth through natural or pruning wounds,
thus hygienic pruning and using (natural) fungicides are very
important to guard against infestation. Grafted trees are said to be
particularly susceptible due to cracks that often form in the tree
structure due to inherent grafting weaknesses. In Thailand, as
previously noted, steps are taken to eliminate a moist microclimate at
the base of the tree which might support the growth of P. palmivora,
such as not using animal manures or mulch, and removing any branches
starting to grow below about 1 m [3 feet] height. Growth of P. palmivora in
Southeast Asia is also controlled by using cultivars known to be
resistant.
Harvest: Grafted cultivars generally start
bearing at 4 to 6 years after planting in the ground; seedlings
usually take from 7 to 10 years but have been known to wait as long as
13 to 21 years—powerful incentives to use vegetative propagation.
Durian fruits vary in size and shape depending on
variety and completeness of pollination, but most often are oblong and
have an average mass slightly larger than a (U.S.-style) football.
Fruit weights of 1.5-4 kg [3 to 10 pounds] are common, but occasionally massive
8 kg [20 pound] (tribal-size!) durians are produced. Of the weight of
a typical whole durian, only about 15% to 25% is fruit pulp and about
20% is seeds, making it one of the most expensive fruits in the world
in terms of its ratio of whole fruit to the part actually edible.
Depending on variety and climate conditions,
it may
require from about 85 to 150 days for durians to develop after flower
pollination, and if not harvested, they will naturally drop from the
tree over about a 10-week period.
In areas near the equator where there are no
defined wet and dry seasons, as in parts of Malaysia and Sumatra,
individual trees commonly bear fruit twice a year, with the peaks in
June and December. In these equatorial areas, durian trees do not
start flowering in response to any seasonal changes in day length or
temperature, but rather are stimulated to flower by periods of dry
weather. In tropical areas with distinct wet and dry seasons, for
example, India and eastern Java, flowering begins near the end of the
dry season. In tropical areas farther than 10º north or south from
the equator, flowering normally starts in the spring months, with an
annual harvest in mid-summer to autumn. There is a tendency with some
trees to bear only every other year, even in areas where twice-a-year
fruiting is possible.
"Initial yield may be 10 to 40 fruits for the
first year of fruiting to about 100 fruits for the sixth year. Yield
of up to 200 fruits is common after the 10th year of fruiting"
—
Durian OnLine
Well-grown, high-yielding cultivars may produce
10 to 15 tons per hectare [9000-13000 pounds per acre] of durian
fruits per year by 10 to 15 years after planting. As durians command
relatively expensive market prices even in the areas of southeast Asia
where they are plentiful, it is easy to understand that in that part
of the world, people who have more than a few bearing durian trees are
considered wealthy.
The two very different approaches
to harvesting
durians
Shunyam
Nirav
As inclined to diversity as the durian is, it’s
not too surprising that two very different basic approaches to
harvesting and eating durians has developed among humans. For
convenience they can be called the Thai approach, which is prevalent
mostly only in Thailand, and the Malaysian approach, which is
prevalent almost everywhere else in Southeast Asia but has been
particularly developed and refined in Malaysia.
In Thailand, it’s customary to harvest durians
from the tree by cutting with a knife (sometimes on the end of a long
pole), when they are approaching ripeness, but not entirely ripe. Like
papayas, bananas, and avocados, durians do ripen well off the tree, if
not cut too soon. Many people (including me) savor Thai
varieties of durians eaten when mid-ripe, somewhat before totally
ripe; totally ripe is usually past their peak of deliciousness. The
Thai durian varieties have evidently been selected and bred over
generations to support this customary harvesting-before-ripe. Part of
the fruit stem (botanically speaking, the peduncle) is always left
attached when the durian is cut from the tree, rather than breaking
off the fruit from the stem. The fruit stem is cut as long as
practically possible, and is often wrapped with a banana leaf or
paper, which is said to extend the fruit’s shelf life.
In Malaysia (and elsewhere), it’s a fundamental
principle that durians should be allowed to naturally fully ripen on
the tree for maximum-quality flavor, aroma, texture, and appearance.
Durian growers wait until the trees naturally drop their ripe fruit,
and collect the fruit several times a day from under the trees. To
prevent damage from hitting the ground or rocks (or people!), either
large safety nets are arranged under the trees to catch the falling
spiky fruits; or workers climb the trees early in the season to attach
long strings or ropes to each developing fruit, which are looped over
branches above and then down to ground level like a pulley, so when
the fruits are dropped by the tree they are caught and can be safely
and easily lowered. Durians in Malaysia are thus regarded as highly
perishable commodities — those that have fallen within the past 12
hours command very high prices in the marketplaces; after 12 hours the
quality is perceived as having diminished and become ordinary, and the
price is reduced. On Penang, at Bao Sheng farm, the best just-dropped
varieties of durians sold in the 1999 season for about the equivalent
of US$3.50 a pound, which meant that a typical 4-pound durian cost
about US$15 for one fruit. That’s at the farm, though; just-dropped
durians are rushed from farms to the cities of Malaysia where the same
durian may readily sell for over twice the farm price. And in durian-crazed Singapore, when swiftly exported fresh-dropped
Malaysian durians of the highest quality varieties are available
there, durian connoisseurs snap them up for the equivalent of US$75
per fruit! For the lowest prices and good fun, large numbers of
Malaysian durian-lovers make pilgrimages to durian farms in various
regions of the country during the season to savor the best
freshly-dropped durians. It’s a real connoisseur scene in Malaysia
around durians — over a hundred officially registered varieties (and
countless more unregistered), all with rich subtle differences of
flavor, texture, aroma, and appearance, and much importance given to
tree-ripening and fresh-droppedness. Malaysian varieties are generally
smaller than Thai durians (rarely as large as a soccer ball), many
varieties have much thinner spikes, and usually the fruit flesh around
the seeds is not as thick as is common in Thai varieties. They usually
have a much more complex and rich flavor than most Thai durians have,
though, and it can be highly variable from fruit to fruit from the
same tree, even from section to section within the same fruit.
It’s evident that Thais and Malaysians have a
good-natured rivalry around their approaches to durians. The
Malaysians disapprove of the Thai practice of harvesting durians
before ripe and letting them ripen off the tree — that’s
unthinkable in Malaysia. To cut durians early and not allow them to
ripen on the tree and drop naturally occurs to most Malaysians as an
insensitive ruination of full-flavored durian quality.
(T.S. Chang of Bao Sheng Durian Farm asserts that durians lose
20% to 25% of their full potential for aroma and flavor by being
harvested early...and I can understand from eating Malaysian durians
what he means.) However, a Thai variety of durian allowed to ripen and
drop from the tree is usually already past its prime. The Thais possess
durian varieties which in their own way are of magnificent quality
when cut, ripened off the tree (like bananas), and eaten at
just the right stage before totally ripe. Having the kinds of durian
varieties they have, Thais don’t understand Malaysians’ (and
others) obsession with tree-ripened fruit and enduring all the
harvesting and marketing challenges and high prices that result. The
practically-inclined Thais do have a commercial advantage with their
approach — cutting durians before ripe has allowed them to develop a
large profitable commercial durian-growing industry, the biggest of
any country. In Thailand, everyone has about a week after harvesting
to transport and market the fruit far and wide, whereas the Malaysian
practice of only accepting tree-ripened durians necessarily greatly
limits their commercial reach and shelf life and makes them very
costly to consumers. Malaysians, however, cheerfully just regard these
things as facts of life that necessarily come with obtaining their
high-quality tree-ripened durians, satisfied that their durians have a
much richer and more complex flavor and better overall quality than
those of their Thai neighbors.
When I visited both countries in June 1999 at the
peak of durian season, the highest-quality durians in Thailand were
selling in the marketplaces for the equivalent in U.S. money of about
50 cents a pound; over the border in Malaysia highest-quality durians
were selling for the equivalent of US$3.50 a pound at the farm, more in
the marketplaces. Durians in Thailand have been made a widespread
commodity that the majority of average people appear to be able to
afford; in Malaysia it appears that durians are in financial reach of
primarily only wealthier consumers (not a criticism, just an
observation of the way things are). However, the big exceptions in
either country are people who grow their own durians...who, if they
have more than a few trees, inevitably become wealthy themselves from
the abundant bounty given year after year by the trees!
As a durian-lover from the outside, I respect,
understand, and enjoy both the Thai and Malaysian approaches and the
resulting fruit. I’ve been fortunate to experience both incredibly
luscious Thai durians (especially Monthong and especially those grown
on the southern islands of Koh Samui and Koh Pha-Ngan, and in the
durian-growing capital of Chanthaburi in eastern Thailand) — and
some of the extremely
richly-delicately-flavored connoisseur creme-de-la-creme Malaysian
durians (especially on the island of Penang). Comparing them isn’t
really fair; at their best they’re both fantastic, unmistakably
durian and yet so different — as similar and yet as different as, say,
Chinese and Japanese humans. And then there are all the other durian
varieties found in Indonesia, Brunei, the Philippines, Vietnam, south
India, and Sri Lanka, with a vast range of subtle differences and
nuances. If you enjoy eating durian and get a chance to be in that
part of the world during the season, visit the colorful local
marketplaces and try as many as you can! Or better yet, if you live in
a tropical area, seek out the
best varieties of grafted trees to grow yourself!
More cultivation information: click
here to view the Durian
chapter (19 pages) from The Production of Economic Fruits in South-East
Asia by Othman Yaacob and Suranant Subhadrabandhu (Oxford
University Press, New York, 1995).
