Osmanthus fragrans, a popular ornamental tree, is widely appreciated for its lush greenery, aesthetic appeal, and pleasant fragrance. Among gardeners, small potted osmanthus has gained significant popularity. However, traditional potted cultivation often leads to issues such as root damage, poor growth, short blooming periods, weak fragrance, and premature flower drop. Additionally, the heavy soil balls used in conventional pots make packing, transportation, and handling cumbersome and costly. To address these challenges, soilless culture technology was developed for osmanthus.
Soilless potted osmanthus requires careful attention to six key technical aspects:
**Variety Selection**
The author selected two main cultivars from the Four Seasons Glutinous group: 'Little Leaf Buddha Top Ball' and 'Jin Mantang'. 'Little Buddha Fodingzhu' is ideal for small pots due to its compact size, full crown, small leaves, early flowering, and abundant blooms. 'Jin Mantang', on the other hand, features strong branching, large crown development, and at least three new shoots per year. Its robust branches and multiple flowering points make it suitable for medium-sized pots or even for grafting onto bonsai trees.
**Substrate Preparation**
Pinewood and Chinese fir sawdust were chosen as the primary substrate for soilless cultivation. However, raw sawdust contains high levels of carbon and low nitrogen, which can release harmful compounds like resins and tannins if not properly processed. To mitigate this, a high-nitrogen fermentation technique was used, along with an acid scavenger to prevent nitrogen loss. This method reduces processing time by at least 30 days compared to natural fermentation while preserving nutrients more effectively.
**Water Management**
A micro-spray system was implemented for daily watering. This system saves time, labor, and water while ensuring efficient hydration. A single worker can manage watering for 50 acres of potted plants each day, significantly improving productivity.
**Fertilizer Application**
To reduce costs and labor, long-term slow-release fertilizers were primarily used. These fertilizers provide a steady nutrient supply over 3–4 months. The author applied "resin-coated urea" + "resin-coated compound fertilizer" + "common sulfur-containing ternary compound fertilizer" during planting in January and again in April. In August, another application of "resin-coated compound fertilizer" + "sulfur-containing ternary compound fertilizer" was made to support growth and flowering. Additionally, every 40 days starting in March, humic acid-based micro-fertilizers like Ye Ye or Jin Nong were sprayed using the micro-spraying system to enhance plant quality and flower performance.
**Pest Control**
Common pests include locusts, spider mites, and crickets. Aphids feeding on young shoots cause leaf damage, affecting both appearance and growth. They can be controlled with 4.5% cypermethrin EC diluted 2000–3000 times or 40% chlorpyrifos EC diluted 1000 times. Spider mites cause yellowing and white spots on leaves, leading to defoliation. A 15% Bailing EC diluted 1500–2000 times is effective against them. For grubs damaging roots, 40% chlorpyrifos EC diluted 1000 times can be used for root irrigation.
**Flowering Regulation**
To control flowering time, potted osmanthus is moved into a greenhouse about 40 days before the Spring Festival. Temperature is maintained between 5°C and 25°C, with a day-night difference of at least 10°C. After 25–30 days, buds appear. High humidity in the greenhouse may trigger diseases, so spraying with 50% Propionine WP diluted 1000 times or 50% mildewen WP diluted 800 times can help. Adding 500-times diluted humic acid micro-fertilizer like Jin Nong improves flower quality and extends the blooming period.
Compared to traditional potted osmanthus, soilless varieties offer better commercial value, lighter weight, easier handling, and a cleaner appearance. Their weight is only one-fourth that of regular potted plants. Sawdust, the main substrate, is abundant and inexpensive, costing just one-seventh of peat or coconut coir. This makes soilless cultivation a sustainable and economically viable option for growing osmanthus.
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