Managing water for durian in the dry season: keep evenly moist, avoid tree shock

Durian is more sensitive to water fluctuations than any other fruit tree. Instructions on how to read soil moisture according to the root layer, correct watering schedule and mulch measures to retain moisture for orchards in the West and Southeast during the dry season.

Summary: The dry season is the easiest time for a durian orchard to "self-destruct" if the orchard owner does not read the soil moisture correctly. Unlike coffee, which can withstand drying for several weeks, durian only needs a sudden dry spell of 3-5 days to be enough to lose its old leaves en masse, causing weak trees to last the entire season. This article collects water management principles specifically for durians — not the general formula for tropical fruit trees.

Applies to: Durian varieties Ri6, Thai Dona durian, Musang King are in the business stage in the Southwest, Southeast and part of the Central Highlands.
Duration: The entire dry season, usually December to April of the following year.
Difficulty level: Medium. Need to observe actual soil moisture, do not water according to mechanical schedule.
Estimated additional costs: About 4-8 million VND per hectare for pumped fuel and covering materials.

Why is durian "difficult" with water

Durian has three characteristics that make water management different from other crops:

Average shallow root system, concentrated in about 60-80 centimeters of topsoil. When this layer is dry, the tree feels it immediately.
Foliage is large, evaporates quickly on a hot sunny day. A commercial plant can "drink" 200-400 liters of water per day during the peak of the dry season.
Leafs are sensitive to salt and water shock: one cycle of alternating dry-watering-drying is enough to make the leaves turn yellow, the plant "goes to sleep" for 2-3 weeks without recovery.

The dry season in the West is shorter than the Central Highlands (4 months compared to 5 months) but is accompanied by saltwater intrusion in coastal provinces such as Ben Tre, Tien Giang, Vinh Long, and Soc Trang. Two overlapping problems — dryness and saltiness — durian orcharding is especially risky in March-April.

Prepare before the beginning of the dry season

[ ] Check water reserves: ponds, ditches, wells. Measure the flow — enough irrigation for at least 5 times in the dry season?
[ ] Measure the salinity of irrigation water if the orchard is in a coastal area. The safety threshold for durian is less than 0.5 parts per thousand. Above 1 in a thousand, the tree begins to suffer.
[ ] Repair the pump system, irrigation nozzle, and drip faucet first. Don't wait until you need it.
[ ] Reserve mulching materials: hay, straw, rice husks or dried leaves. About 8-12 cubic meters per hectare.
[ ] Cut diseased branches, dry branches, and dense branches in the canopy. Airy canopy reduces evaporation.
[ ] Fertilize the base before entering the dry season — mainly potassium and phosphorus, limited nitrogen.

For areas with saltwater intrusion, it is necessary to add:

[ ] Dig a pond to store fresh water for 1-2 months of use.
[ ] Install a handheld salinity measuring device. Price is about 800 thousand to 1.5 million VND — worth the investment.

Irrigation process during the dry season

How to read soil moisture accurately

This is the most important skill. Whether or not you water enough is not determined by the calendar but by the actual humidity.

The most common way is to use your hands: dig 15-20 centimeters deep at the edge of the canopy, take a handful of soil, and gently squeeze it.

The soil is compact, does not leak water, feels cool to the touch = moderately moist.
Loose soil, squeezed without clumping = dry. Need to water immediately.
Soil is mushy, water leaks out when squeezed = too wet. Stop watering.

The more accurate way is to use a handheld moisture meter. About 500-800 thousand VND, measured right at the base. The edge of the canopy is where the main root activity is, not close to the trunk.

Irrigation dose according to plant stage

Unlike coffee, which is watered in long batches, durian is watered evenly and divided into small parts:

4-7 year old trees: 80-120 liters per tree per day in dry peak. Divide into 2 times — early morning 5-6 o'clock and late afternoon 16-17 o'clock.
7-15 year trees: 150-250 liters per tree per day. Divide 2-3 times.
Trees over 15 years old: 250-400 liters per day. Can be divided into 3-4 times in areas with strong sunlight.

The irrigation method determines the effectiveness almost as much as the dosage:

Water slowly, allowing the water to absorb evenly — about 30-45 minutes for a tree with a root tip.
Do not pour all the water in 5-10 minutes. Water flows to the deep layer, not entering the active root zone.
Avoid sprinkler irrigation on the canopy. The leaves are wet and the strong sun at noon causes the leaves to burn and become speckled.

Covering — small investment, big benefits

A 6-8 centimeter thick layer of mulch with hay, straw or rice husks reduces soil evaporation by 40-60 percent. I have seen many Western orchards skip this step even though the cost is low.

Covering rule:

Spread as wide as the tree canopy, not just around the base.
Leave about 15-20 centimeters of open space at the root neck. The root collar is moist and the air is trapped, which is where the root fungus thrives.
Materials must be damaged. Green straw absorbs nitrogen as it decomposes — the plant will lack nitrogen.
Do not cover with plastic. Beautiful but the soil is stuffy and the roots are suffocated.

Handling saline intrusion areas

Western coastal orchards experience saltwater intrusion in February-April. Principle:

Measure water salinity before watering. Above 0.5 parts per thousand should not be watered.
Storage fresh water into the pond during last year's rainy season.
When there is no fresh water, priority is given to drip irrigation — small amounts, deep into the root layer, reducing salt accumulation at the ground level.
Spray leaves with amino acids and calcium to help plants better withstand saltwater.

The orchard has had its roots eaten by salinity: 30 percent reduction in expected yield this season. Priority should be given to saving plants through the dry season, not forcing them to flower.

Follow up every 5-7 days

[ ] Leaf condition: unusually old leaves falling is a sign of lack of water or fungus at the base.
[ ] Bud color: glossy dark green is good. Pale yellow means lack of protein, dark yellow means the root has a problem.
[ ] Soil moisture at three different points in the orchard — high and low areas is always different.
[ ] Irrigation water flow compared to last week.
[ ] Are there any signs of stem borers and mealybugs appearing in the dry season?

Troubleshooting

Leafs turn yellow quickly and fall off: check immediately to see if it's due to sudden dryness. If the root is still moist but the leaves are still yellow, strip the mulch to see if the root collar has fungal symptoms.

The plant wilts even though it has just been watered: the roots are infected with fungus or nematodes. No matter how much water you water, the water does not penetrate the plant. Treat the root with fungicides early.

Suddenly salty water: stop watering, measure water salinity during the day. If salinity is still high, just water sparingly from the freshwater reserve pond.

Five common mistakes

Watering a lot at once and then letting it dry for a few days: creates extremely harmful humidity fluctuations. Shocked tree, mass of yellow leaves.
Irrigate close to the trunk: roots work at the edge of the canopy, not close to the trunk. Watering close to the stem is both wasteful and causes root fungus to grow.
Irrigation at noon: 30-40 percent evaporates before water penetrates the soil. Early morning and late afternoon are effective.
Skip mulching because it's "wasting effort": a few hours of mulching at the beginning of the dry season saves 30 percent of water for the whole season.
Irrigate while the soil is still moist "to make sure": local waterlogging causes roots to suffocate. Waterlogged durian is as dangerous as dry.

Notes during the dry season

Minimum recording per week:

Watering date and estimated water amount.
Water salinity if coastal area.
Observable leaf condition — color, shine, shedding.
Weather: sunny, windy, light rain if any.
Fertilizing or spraying supplies for the week.

At the end of the dry season (April-May), summarize: amount of water irrigated per hectare, number of saltwater intrusions, percentage of trees showing signs of decline. This data is used to better prepare for next year's dry season.

References

*Technical process of durian cultivation in the Mekong Delta* — Southern Fruit Institute, 2023.
*Water management for fruit trees in saline intrusion areas* — Department of Crop Production in coordination with the Southern Institute of Water Resources Science, 2022.