Key Technical Points for Seed Collection, Storage and Seedling Cultivation of Korean Pine

1. Seed Collection and Processing

Korean pine is a monoecious species with unisexual flowers; its flowering period is in mid-to-late June, and it takes 15 months from flowering to cone maturity. The seed collection period for Korean pine can last up to 4 months; in the early stage, cones can be picked or knocked down from the trees, and in the later stage, cones can be picked up from the snow. After collection, the cones are spread out to sun-dry or air-dry in the shade for several days; when the scales slightly open, they can be processed by beating with a stick by hand. The seed extraction rate of cones from natural forests is 13%-14%, while that of cones from plantations can reach 30%, with a 1000-seed weight of 520 grams. During seed collection, attention should be paid to the selection of cones, and during seed processing, small seeds should be screened out to ensure seed quality and high-quality, high-yield seedlings. The seeds must be dried until their moisture content drops to 10% before they can be stored.

2. Seedling Cultivation Methods

Seed treatment. First, seed cleaning. Korean pine seeds are large, and the sowing rate per unit area is high; generally, first-grade seeds are sown at 0.5 kg per sq m. Typically, the seeds are soaked in clean water for 24 hours, the floating seeds are removed, and the sunken seeds are retained. Second, seed disinfection. Korean pine seeds require a long stratification period; if not disinfected, they are prone to mildew and rot. Before disinfection, soak the seeds first, then soak them in a 0.5% sulfuric acid aqueous solution for disinfection for 3 hours, remove the seeds and drain them, and prepare for sand stratification. Third, seed stratification. Korean pine seeds have a long dormant period; without sufficient stratification treatment, they will not emerge in the year of spring sowing or will emerge unevenly.

Indoor natural-temperature stacking method. In mid-to-late August, soak the seeds in water for 2 days, mix with twice their volume of sand, maintain 60% humidity, and place indoors in a pile 30-40 cm high, turning once every other day and watering when dry. When the weather turns cold and freezing, pile them 60 cm high and water to seal in the frost. Before spring sowing, turn the pile to make temperature and moisture uniform.

Rapid stratification method. 40 days before sowing, soak the seeds in 50-degree hot water and stir thoroughly until the water temperature drops to 30 degrees. After 24 hours, replace with cool water, then replace with cool water once every two days, soaking for 10 days. When the seed kernel turns milky white, remove the seeds, evenly mix with 3 times their volume of moist sand, and spread them out to sun in a wind-sheltered, sunny place. Each evening, pile the seeds up and cover with a straw curtain, then spread them out again the next day. To speed up stratification, they can be placed indoors with appropriate heating, maintaining a temperature of 20-30 degrees, turned twice daily and watered evenly to maintain a certain humidity.

With the above two methods, when more than 30% of the seeds have cracked open, stratification is considered good and they can be used for sowing.

Sowing time and method. When the temperature at 5 cm below ground in spring reaches above 8 degrees, sowing can begin. The sowing rate (calculated on a dry-seed basis) is 200-250 kg per mu. Use a seeder to sow the seeds on the bed surface, then press them down so that the seeds are in close contact with the soil, then cover with humus soil or sawdust to twice the depth of the seeds, and press down once more. If sawdust is used as cover, it must be watered thoroughly.