Pruning and Training The Durian

Outline:

• Modern Durian
• Durian Tree Architecture
• Why Prune Durian?
• When To Prune Durian
• Low-Head Training System (LHTS)
• Training and Pruning Procedures For Low-Head Training System
• Training and Pruning Procedures For Modified or Delayed Open-Center Pruning System
• Pruning to Control Canopy of Durian (Thai technology)
• Pruning Neglected Durian Trees

Modern Durian

The common durian has been cultivated for centuries at the village level in south-eastern Asia probably since the late 18th century. As a backyard fruit tree, the durian receive little or no horticultural attention but allow to grow and bear fruits naturally.

It was only during the early 1930's that local scientists and durian growers began collecting and evaluating the many different durian cultivars in an attempt to select high quality durian based mainly on the fruit characteristics prefer by consumers.

During the 1970's, many fruit farmers, especially in Thailand followed by Malaysia and Indonesia, started to open up large durian orchards and planted popular durian clones on a large scale. They began to manage the durian orchards as a commercial enterprise because the durian has become very popular and good quality durians are scarce and in high demand, not only to the local people, but to durian lovers all over the world. This is the beginning of the modern durian that we so commonly see today.

While the older durian are generally left to grow and bear fruit without much care and attention, the modern durian, on the other hand, require professional and intensive management to produce a good crop of high quality fruits. And pruning and training the durian tree, especially during the early years after planting, is one of  the most important tasks that must be carried out properly and at the right time. There after, the durian requires regular pruning to keep it healthy and strong.

Durian Tree Architecture

It is important to understand the durian tree architecture in order to carry out the proper pruning procedures. The common durian (Durio zibethinus L.)  has been assigned to the model of Roux which is characterized by having a monopodial orthotropic trunk and plagiotropic lateral branches. Some orthotropic laterals are also produced which eventually compete with the main axis. Durian has diffuse growth rather than rhythmic growth.

In simple terms,  the durian has a definite main, central vertical trunk and the lateral branches grow at an oblique or horizontal angle from it. Some vertical or erect branches are also produced which eventually compete with the main trunk. Shoot growth is continuous rather than seasonal.

A magnificent seedling durian tree
with height more than twice that of an electric pole.

 In its natural state, durian trees are large evergreen tropical forest trees. They can reach heights of 45 m (or 150 feet) and the first branch can be 18 m (or 60 ft) from the ground. Matured trees are usually buttressed and the trunk has an average diameter of 56 cm and can reach up to more than 100 cm. Durian grown from seeds usually have a tall trunk with an irregular, dense or open crown of rough branches.

Durian's buttressed trunk with
  irregular and undesirable erect branches

.

 

The continuous and twisted growth of branches of
an un-pruned durian tree grown from a seed.

A seedling tree with durian fruits located high up in the branches 

A modern durian orchard with grafted durian clones

Modern durian trees are usually bud-grafted clones and they are easy to spot because they have been pruned to a distinctive characteristic cone or semi-circular shape tree, and the branches are well-distributed around the main trunk. If no pruning is carried out, grafted clonal trees will eventually grow into the same irregular branching and tall form as seedling trees, but with a maximum height usually only about half as great.

 Left: Un-pruned tree that has too many upright and unproductive branches

Right: A bud-grafted durian clone that is pruned to the desired shape

 

Bioversity International published a booklet on "Descriptors for Durian" (you can get a free copy HERE) and listed six common canopy or crown shapes as follows:

It also listed down three common tree growth habits as follows:

The following are crown or canopy shapes of some of the popular Malaysian durian clones:

The popular clone D24 or "Sultan" has a semi-circular or dome shaped canopy.

Cone-shaped canopies of clones D145, D123 and D169

Durian clone D159 is cone-shaped while clone D158 is elliptical shaped.

Clone D199 is similar to D24 and has a semi-circular or dome shaped canopy

Table 1: Tree Characteristics of Popular Durian Cultivars
From Malaysia, Thailand and Indonesia

Why Prune Durian?

Durian trees are pruned to:

• develop a strong tree structure and vigorous canopy shape that facilitate horticultural practices and enhance fruit production and quality; and

• ensure trees are vigorous and healthy and at least risk to diseases and insects.

In a durian orchard, during the first few years after planting in the field, the young durian trees are pruned or trained by removing vertical laterals or branches. Pruning dominant upright branches to maintain one central leader and a well-balanced canopy is essential to establish a strong tree structure for maximum fruit production.

Pruning or thinning out undesirable branches or laterals and establishing  a well-balanced branch spread around the trunk ensure free circulation of air and sunlight penetration necessary for fruit buds to develop and fruit to mature properly. The common durian flowers are ramiflorous, i.e. the flowers are borne along big branches that are capable of bearing the weight of mature fruits. Durian trees bear fruit best on branches that are more or less horizontal; upright branches contribute more to tree size and height.

The common durian are ramiflorous, i.e. the flowers and fruits are borne along big branches 

Topping or heading is pruning the main trunk to control tree height and branch spread so as to facilitate many horticultural tasks such as spraying, hand pollination of flowers, fruit thinning and harvesting.

Diseased or insect damaged branches must be pruned as soon as possible to prevent its spread. Dead, broken and weak branches as well as water-shoots are regularly pruned especially after the fruiting season.

When To Prune Durian

Durian trees should be pruned or trained while they are young and matured trees are also pruned on a regular basis in order to produce plenty of good quality fruits. It is important to understand the principles of pruning the durian and to prune for a specific purpose.

In pruning a newly-planted durian tree you should select and develop branches to be the fruit-supporting framework of the tree.  After these scaffold branches have been selected, only a limited amount of pruning will be necessary until the tree comes into full bearing.  Too much pruning on a young tree may delay fruit bearing for 1 or 2 years longer.

 The branch structure of durian trees will vary with the clone or variety of the durian.  Some branches will develop at the desired spacing and angle on the tree trunk.  However, other clones will not have branches develop as you desire.  In these situations, try to follow the pruning principles and develop the best structure you can.

Methods used to train young durian trees may either be a “central leader” or “open center.”  Durian trees are generally pruned to the central leader method. However, in Thailand many durian farmers practise the open center method as it usually produce more fruit and facilitate hand pollination, fruit thinning and harvesting.

Pruning and training to achieve a strong central leader

Low-Head Training System (LHTS)

During the early 1990's, the Malaysian Agricultural Research and Development Institute (MARDI) introduced the Low Head Training System (LHTS)  to replace the conventional high-headed training system which has been traditionally practised in older durian orchards.

High-headed durian trees generally grow taller and bear fruits mostly in the upper part of the canopy leading to high management cost. The main difference between the two systems is the height of the primary branches from the ground which is maintained at 75 to 100cm for the low-head system and more than 1m for the high-head system.

Low branching in low-headed durian trees reduce apical dominance of the central leader and control of tree height. Low-headed durian trees required little pruning, begin fruiting a year earlier and yield nearly twice as much as high-headed durian trees.

Training and Pruning Procedures For Low-Head Training System

Training during the year of planting and the following year is very important since you will be selecting the scaffold or fruiting branches.  Here are some pruning and training suggestions for each year after planting until the durian tree bears fruit at about the 5th or 6th year.

First Year: Year of planting; ensure seedling is growing erect

Many durian farmers used older seedlings known as "Advance Planting Materials" (APM) for planting. These are bud-grafted clonal seedlings which are 24 months or older with plant height reaching to 1 meter or more. They have a main stem diameter greater than 15mm and 5 to 8 branches. APM's have a better survival rate after field planting and come into fruiting very much earlier but they cost more than normal seedlings and management cost is higher because of its bigger and heavier size.

 

 An Advance Planting Material that's more than 1 m tall

First Year

During the year of planting, the most important task related to durian tree training is to ensure that the main stem is growing straight up. If it is growing away from the center of the tree, it may need to be pulled into a vertical position and tied to a stake placed beside the tree trunk.

Second Year:  Developing the tree framework is the main objective this year

Second Year

Usually the main stem is selected as the central leader as it is the most vigorous among all the upright growing branches. 

Select 5 to 8 branches that form wide angles with the trunk and are evenly distributed on the different sides of the trunk.  They should be at least 15 cm apart and the lowest branch about 75 cm above the ground. If necessary, the scaffold branches should be pruned at the ends so they are about 15 to 30 cm shorter than the leader.

Some additional tree training can be done during the vegetative growth, such as removing undesirable shoots as well as spreading scaffold limbs so they develop at a wide angle with the trunk.

Limbs can be spread by using bamboo or wooden sticks cut to proper lengths to spread limbs to wide angles with the trunk.  The angles should be over 45 degrees and less than 90 degrees.  Be careful not to split the branches at the point of attachment as you put the sticks in place.

A wooden stake can be driven into the ground and a soft material such as nylon tied onto the branch to pull it towards the stake and spread it.  Generally, limbs should be spread for at least one growing season. The spreading of 1-year-old scaffold limbs should progress up the tree until all the scaffolds have been spread.

Third Year:  Topping or pruning the growing tip of the leader is the main objective this year

Third Year

Ensure the central leader is growing straight. It may need to be pulled into a vertical position and tied to a stake placed beside the tree trunk, if it is growing away from the center of the tree.

The leader should have grown taller and bigger. Now is the time to prune the leader. Topping or heading is pruning back the leader to an outward growing branch.

Topping the leader: 1 - First cut; 2 - Second cut

Select the most vigorous and closest outward growing branch. At the point of union to the main trunk, prune back the central leader to a height of 1.5m. Ensure no other side branches are competing with this chosen branch that will become the new leader.

Topping will encourage the growth of more primary branches. If necessary, select 2 or 3 more primary branches growing from the leader for more scaffold branches.  Compare the length of them with the leader and prune them 15 to 30 cm shorter than the leader.

Scaffold branches developed in previous year will have formed secondary shoots. On each scaffold, save 2 to 4 of these new shoots that are growing 15 cm or more away from the leader of the scaffold branch.  Shorten any that are longer than the leader of the scaffold.

Each scaffold should be pruned as though it were a young tree. The main difference being that the secondary branches should be primarily on the same plane as the scaffold.

Prune the scaffolds of the tree so they are in balance.  Do not let lower branches out grow the upper portions of the tree, nor the upper branches grow longer and “shade-out” the lower ones. The overall shape you are trying to develop and maintain is an inverted cone or pyramid.

Fourth Year:  Open up the center of the canopy

Fourth Year

Continue formation of the fruiting scaffold branches of primary and secondary branches.

Open up the center of the canopy by pruning or thinning secondary branches within. This will allow better air ventilation and more sunlight to penetrate within the canopy. 

To achieve a well-balanced tree, do not let the primary branches compete with the main trunk. The size of primary branches should not grow more than 30% of the main trunk. Use the "bench-cut" method to control the primary branch growth and to create a more open canopy. This involve the pruning of about one third the length of the primary branch.

Pruning or thinning out undesirable oblique branches and branches that form narrow “crotches” should be removed to give the durian a well-balanced, stable and strong structure against wind damage and able to support plenty of fruits.

Continue with the regular maintenance pruning by removing dead, damaged, broken or diseased branches and water-shoots.

Durian clone (6 to 7 years old) pruned according to the low-head training system

Training and Pruning Procedures For Open-Center Pruning System

Some durian farmers in the Eastern Region of Thailand generally practiced a modified or delayed open-center pruning and training system for their durian trees. It's looks like a 2-tier system similar to that used for many temperate fruit trees.

First Year: Year of Planting

During the first year of planting, the main stem or central leader is pruned to about 20-30 cm above the grafted union. From the first year of vegetative growth, 3 to 4 branches are selected and developed into the fruiting area as the first tier.

The selected branches should form wide angles with the trunk and are evenly distributed on the different sides of the trunk. They should be 10 to 15 cm apart and the lowest scaffold about 20 to 30 cm above the ground.  These branches should developed uniformly in size and then pruned to about 20 to 25 cm in the second year.

 

First year

Second and Later Year to Bearing

Select shoots which develop from this first tier of scaffold branches to be trained as the second tier of fruiting branches. Remove any shoots other than those chosen for the scaffold framework. Prune the scaffolds to equal lengths so they grow at about the same rate.

Other corrective pruning includes removing branches with poor crotch angles, that are growing through and across the tree, and that are broken or showing disease or insect injury.  Usually a young tree needs very little other pruning.

The canopy is developed to spread out like an opened umbrella or an inverted pyramid. The tree height  is maintained at about 3 to 4m with the canopy size at about 2 to 3m and the supporting main trunk at about 70 to 100cm. Any new shoot growth above the desired height of 3 to 4m is cut away thus reducing apical dominance in the upper portion of the canopy. This forces the tree to redirect its growth to develop the lower portion of scaffolds or fruiting branches.

Second and later year

With intensive farm management practices for fertilizers, irrigation and insects and diseases control, the young durian trees will start to bear fruits as early as 4 to 5 years for Monthong and Chanee cultivars , and 5 to 6 years for Kanyao cultivars.

 

To maintain quality, Thai farmers only keep 
10 fruits from a durian's first year of bearing

Supporting the fruiting scaffolds with
wooden stakes or bamboo

Low branching of a well-pruned durian tree

 

A modern durian orchard

 A proud Indonesian farmer admiring his quality durian

A young durian laden with fruits

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Reports from Thailand are few and they are mostly written in Thai. The following is an excellent report on pruning for durian written by Surmsuk Salakpetch from the Chanthaburi Horticultural Research Center, Chanthaburi, Thailand.

Pruning to control canopy of durian

In Thailand, durian plants are normally propagated by grafting or inarching (approach grafting) and the position of the graft should be at about 30-35 cm. above ground level. This results in a reduction in the risk of phytophthora disease occurring in the scion.            

When cultivated under orchard conditions, durian trees are distinctly pyramidal in shape, while in trees grown under jungle conditions or under jungle-like conditions the lower branches are self-pruned and the bearing branches will be very high overhead in the canopy.                 

 Therefore, it is important to pay a great deal of attention to the training and pruning of durian trees when grown under orchard conditions.

 Training and pruning juvenile trees
Pruning should be carried out regularly from the time of planting to build up a strong framework of branches.        

The following practices are employed:
             

• When durian plants are established after transplanting, the first objective is to ensure that 4 to 6 strong, lateral and wide-angled branches are selected as the main or primary limbs and the lowest branch should   remain at least  60cm  above the ground level. These branches should be about 10 to 15 cm apart, increasing to 30 cm apart in the mature tree.
• Remove lower branches to allow only one main trunk to develop.
• Remove water sprouts, water shoots, narrow-angled and open-angled limbs and any unhealthy shoots.
• A year later, another 6 strong, lateral and wide-angled branches are selected as the main or primary limbs. At this stage, about  10 to 12 primary limbs should be developed and the highest branch should be about 2 meters above ground level.
• When durian plants are 3 years old after transplanting, the lowest branch should be about 1 meter above ground level.  In this case, 1 to 3 lower primary limbs can be cut. 
• To encourage vigorous growth of the primary limbs, secondary and tertiary limbs should be removed. This results in production of long primary limbs. The length of primary limbs represents the canopy size.

Pruning mature trees
              
Since durian produce flowers and fruits on branches, strong healthy and productive branches should be left on the tree. Productive branches should have a diameter of about 4 to 10 cm  and are in the position that they  can  receive a photosynthetic photon flux density (PPFD) more than 90 µmol m-2 s-1. Unproductive branches have diameters wider than 10 cm or less than 4 cm.  The current practice to encourage production  of the productive and strong healthy branches is as follows.
              

• Excessive small branches inside  the  canopy  should  be  removed  to  increase ventilation and light penetration in the canopy.  Branches that receive PPFD less than 90 µmol m-2 s-1 are unable to produce new vegetative shoots and can dry up and die.
• When the diameter of primary limbs close to 10 cm, the secondary branches should be encouraged to increase number of productive branches.              
• Immediately after harvesting, complete fertilizer such as 16N-16P2O5-6K2O and cow manure are applied to strengthen the tree. The damaged, diseased, dried and unused branches should be pruned off to promote the emergence of new shoots.
• The main trunk and the primary limbs can be topped and trimmed  regularly to obtain a desirable shape of the canopy so that the cultural practices described above can be employed in an efficient manner.

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Pruning Neglected Durian Trees

A matured durian tree left to grow without any pruning

A neglected durian tree that has not been pruned for several years, if at all, has irregular branches causing heavy shading, poor ventilation, high risks to diseases and wind damage. Fruit production is generally very low or no fruit is produced.  The tree is usually too tall, therefore, many horticultural practices such as pruning, pest control, hand-pollination, fruit thinning and harvesting are difficult.

However, if the tree is moderately healthy and has some strong scaffold branches, it may have potential to bear fruit for several years.

Don’t be afraid to prune.  Develop a mental picture of a well-formed tree and use it as a guide as you prune.  No two people are likely to prune a tree exactly the same way but the objectives in pruning should be observed. Excessive pruning at one time may cause the durian to fail to bear fruit for 1 or 2 seasons.  Two or three years may be necessary to fully prune a neglected tree.  As a general guide, not more than one-third of the total wood in a durian tree should be removed in one pruning season.

By making decisions and pruning cuts in four stages, a neglected tree may be revitalized.  Study your tree to identify some of the major problems.

Step 1: Prune wood around the trunk area and near the ground so you have best visibility of the tree.

• Remove all water-shoots around the trunk.
• Remove all branches that hang too close or touches the ground.  Prune them off at the supporting limb.

 Step 2: Stand back and study the tree again and decide the cut to make next.

• Retain scaffolds that are growing away from the tree center at wide angles with the trunk. Scaffolds     should be positioned on different sides of the tree for good distribution of the fruit crop.
• Remove scaffold branches that are crowded, growing vertically, and growing too close together causing heavy shade.  The specific limbs you remove usually are not as important as the fact that they are removed to increase light penetration into the center portions of the tree.

Step 3: Lower the height of the tree to a desired level for easy care.

• Determine the approximate height you would like to have the tree, then cut the tall branches off at supporting horizontal branches. Most farmers do topping or heading of older durian tree at a height of 7 to 8m: slightly higher than the 5 to 6m desired height of a durian seedling pruned from the early years of planting. The extra canopy at the top protects the middle and lower portions of the canopy from getting "sun-burn" from the hot sun. The top branches also provide "anchors" for tying lower branches that are fruiting during the season.
• Reduce the spread of the tree in the same manner. Use the "bench-cut" method to control the branch growth and to create a more open canopy. This involve the pruning of about one third the length of the branch.

Step 4: From the remaining branches, thin out branches that cross over, hang down, are too long or too close together, and are damaged or diseased.

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