Citron, also known as *Torreya grandis*, is a species of eucalyptus belonging to the genus Polygonaceae. It is an evergreen tree that can grow up to 30 meters tall with a trunk diameter of about 5 meters at breast height. The bark features irregular longitudinal cracks, and all parts—branches, leaves, and wood—emit a distinct camphor-like aroma. The leaves are alternate, thin and leathery, oval or ovate-elliptic in shape, measuring 5–10 cm in length and 2.5–5.5 cm in width. They have an acute or subapical tip, a broadly cuneate or nearly round base, and entire margins with slight undulations. The leaves are hairless on both sides, with three prominent veins originating from the base, and pinnate venation with noticeable glandular pits. The petiole is 2–3 cm long.
The flowers are bisexual and arranged in axillary panicles. The fruit is nearly spherical, initially green and turning red as it matures, eventually developing a shiny purple color. The fruit has a truncated top, and it ripens between October and November. Citron thrives in warm and humid climates, where the average annual temperature exceeds 16°C, and the minimum temperature does not drop below -7°C. It prefers deep, fertile, and moist neutral or acidic soils. Young trees are shade-tolerant, while mature trees are strong and long-lived. These trees are often found near villages, where they serve as landmarks.
Propagation of *Torreya grandis* is primarily done through seeds, though hardwood cuttings, root cuttings, and tillering can also be used, albeit with lower survival rates. Seed collection should be done from well-developed, mature trees between October and November. When the fruits turn red and purple, they naturally fall, so timely harvesting is essential. Seeds should be processed immediately after collection to prevent heat accumulation and embryo damage. After washing, the pulp is removed, and the seeds are defatted in ash for 12–14 hours before being dried. The seeding rate is around 25–30%, with 1,000 seeds weighing 120–130 grams, and approximately 7,600–8,000 seeds per kilogram. Germination rates are typically 80–90%. Seeds can be sown in autumn or stored in wet sand until spring.
In the nursery, shaded and wind-protected areas are ideal. Soaking dry seeds in warm water or storing them with sand can improve germination. Sowing usually occurs in mid-February, but if temperatures are low, it can be delayed until mid-March. The seeds are planted in furrows about 3 cm deep, with 40–50 seeds per meter. Covering with humus or fire soil and grass helps retain moisture. Germination takes 40–50 days, and seedlings emerge over 50–60 days. Seedlings are transplanted when they have 3–5 true leaves, and proper watering and fertilization are crucial during their growth period. Annual seedlings reach 30–50 cm in height and can be planted in the field.
Transplanting large trees of *Torreya grandis* is common, especially for urban greening projects. Trees with a trunk diameter of 10 cm or more are typically selected. The best time for transplanting is early spring or late autumn, before the ground freezes. Crown pruning, root reduction, and cut-dry methods are commonly used techniques. Proper care, such as wound protection, root wrapping, and post-transplant watering, ensures higher survival rates. Shading and winter protection are also important for newly transplanted trees. Overall, *Torreya grandis* is a valuable species for both ecological and aesthetic purposes, enhancing urban landscapes and providing environmental benefits.
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