Opinion of the ancients that longan tree is difficult to flower because that plant is male and should be planted a pair is not true. The flowering of longan is not related to the sex of its flowers, because longan has inflorescence and there are male (Male 1) and female (Female) flowers in each panicle, and there are some varieties that have hermaphrodite flowers (Male 2). So, how could it be deduced that a longan plants were male or female if it does not flower yet?
The difficulty of longan plants to flower is because the plant comes from subtropical areas where low temperature plays an important role in flowering. Thus in Indonesia, longan plants could initially produce well in the area having a low temperature of at least 2 months during the dry months, including Temanggung, Ambarawa and Batu.
Traditional farmers in Thailand initially spray or give ice around the plants to condition the environment around the plant to a stable low temperature. This conventional treatment is not being carried out anymore as the discovery of chemicals that are able to induce the plant flowering. This finding is what makes Thailand as one of the largest longan fruit producer.
In Indonesia there are several varieties of longan plants that are difficult to flower both lowland and highland, including Itoh, Kristal, New Kristal, and so on. The treatments that can be done to induce flowering of longan plant are:
- Physical treatment by wounding the plant stem. For example, by scrapping or exfoliating the cambium in the main stem. This method is cheaper but its application is less measurable.
- Chemical treatment by applying a chemical inducer. This method is more measurable and has higher success rate than the physical one. The application method can be done in three ways:
- Watered on the ground under the canopy/root zone
- Sprayed onto the leaves
Injected into the main trunk or the roots of the tree, this way is done on a large longan plants that are difficult to water or spray.
Based on research, chemical treatments by watering have a higher success rate. The chemicals used are strong oxidizing chemicals, one of which is KClO3. This material is often used as explosive material so that prudence in the use of it is very necessary. Products containing these active ingredients include Longan Booster, Vita Longan and Nong Feng.
Requirements for chemical treatments application are:
- No rain after treatment. Rain will cause the chemicals given will be washed before the plants absorb it. This will cause low success rate.
- Plants that are ready to be treated are 2-3 years old plants with a plant height of at least 2 m and canopy width of ± 1 m2.
- The leaves at the time of application are old leaves, if the leaves are young, flowering chance will be low.
- Plants can be treated again after the second vegetative/flush period.
If these requirements are met, then the technical applications of chemical treatment by watering are:
- Clean the soil under the canopy from gravel, trash, and weeds.
- Do some pruning if the crop canopy is too dense for sunlight entry and good air circulation. Trim branches with young leaves at it ends.
- Dissolve the chemicals in water according to the dosage recommendation of the product.
- Pour the solution to the ground at the outer edges of the plant canopy.
- A week after treatment, apply NPK fertilizer with dose according to plant age (2-3 yrs = 0.2-0.5 kg; 4-5 yrs = 0.5-1 kg; >5 yrs = 1-1.5 kg).
- Water regularly.
By: Buyung Al Fansuri, SP
Researcher at Indonesian Citrus and Subtropical Fruits Research Institute
Agency for Agricultural Research and Development