In the Sakju district of the North Phyong-an province, there is a reserve established to protect and multiply the so-called Japanese cucumber belonging to the flora of the temperate zone.
Other tall, climbing plants and shrubs such as holm oaks, wild walnut trees, linden trees and pines grow there, forming a lush forest.
The reserve occupies approximately two hectares.
The trees are 22 – 25 m in average height, 81 – 82 cm in perimeter of the root neck and 20 – 25 cm in diameter at chest height. They bloom in mid-May and the fruits fully ripen in early October. About 10 kg of seeds are collected from a tree.
As a natural monument of the country, this grove enhances the landscape and has great importance in the ecological study of this variety.