Detailed Explanation of Key Technical Points for Overwintering Cucumber Seedling Cultivation

Overwintering cucumbers refer to cucumbers grown in solar greenhouses, sown in autumn, harvested starting in winter, and continuing until late spring or early summer of the second year. This crop is also called the overwintering main crop, or the "winter-spring crop." Overwintering cucumber production goes through the season with the poorest sunlight and lowest temperatures of the year, making it technically demanding and requiring strict standards, but it also yields the best economic returns of any crop.

??I. Basic Conditions Required for Production

Using solar greenhouses for overwintering cucumber production is based on no heating or essentially no heating (limited temporary supplemental heating), so greenhouse construction and management requirements are strict. Regardless of the structural form of the high-efficiency energy-saving solar greenhouse used, the temperature during the harsh winter season must meet the most basic needs of cucumber growth. Under normal management, the minimum temperature in the greenhouse should not be lower than 8°C. In regions with severe cold and poor sunlight conditions, temporary supplemental heating measures can be taken to ensure the indoor temperature reaches the critical limit or is slightly higher by 1-2°C.

???II. Varieties

Overwintering cucumbers currently mostly use grafted seedlings, and the scion varieties have strict requirements: they must set fruit normally under low temperature and weak light; they must also tolerate high temperature and high humidity, with strong fruit-setting ability under such conditions and producing many second-crop fruits; in addition, they must have good disease resistance and strong adaptability to the greenhouse environment. Currently, the most widely used in production are the dense-spine types, including Changchun Mici, Xintai Mici, Shandong Mici, Jiza No. 1 and No. 2, Beijing 102, Jinlv No. 3, and others.

???III. Sowing Period

Overwintering cucumbers generally have a seedling age of about 35 days, and harvesting begins about 35 days after transplanting, with about 70 days from sowing to harvest. Overwintering cucumbers are generally required to begin harvesting around New Year's Day, so as to enter the peak production period around the Spring Festival. Calculating from this, the normal sowing period should be from early to mid-October. Sowing during this period is beneficial for graft wound healing and for building a high-yield framework before the harsh winter arrives. To increase pre-winter yield and reduce overwintering risks, the sowing period can also be appropriately advanced.

???IV. Grafting and Seedling Cultivation

Cultivating overwintering cucumber seedlings is generally carried out in solar greenhouses. Generally, cucumber seeds should be sown 5-7 days earlier. When the squash cotyledons have flattened and the first true leaf is half-unfolded, and the cucumber has 2 true leaves and 1 heart leaf, it is the suitable time for grafting. If black-seed squash seedlings are too large and become hollow, it will affect the grafting survival rate. Currently, the approach grafting method is most widely used for overwintering cucumber grafted seedling cultivation. There are 3 methods for approach grafting: first, sow and raise cucumber and black-seed squash seedlings in separate beds, dig up the seedlings separately at grafting time, and transplant them into another bed after grafting; second, sow cucumber seeds in a sand bed by broadcasting, and after sprouting black-seed squash seeds, dibble them into nutrient pots (in the center position); at grafting time, only dig up the cucumber seedlings, then temporarily plant the cucumber seedling roots to one side of the nutrient pot, place them in the seedling bed for cultivation, and manage them by moving the nutrient pots according to seedling conditions; at transplanting time, the seedlings are easy to transport and the roots are not easily damaged; the third method is to sow squash seeds directly on the bed ridges, dig up cucumber seedlings at grafting time, and after grafting, temporarily plant the cucumber seedling roots to one side of the bed ridge. These 3 methods each have advantages and disadvantages, but the latter two methods facilitate seedling recovery, yet require skilled grafting technique to ensure the grafting survival rate. For the first 3 days after grafting, maintain a temperature of 25-30°C and humidity of 90-95%, then gradually lower the temperature and humidity. Through careful management, cultivate robust seedlings that are 10-15 cm tall, 0.6-0.7 cm thick, with 4 leaves and 1 heart leaf, and a seedling age of 35-40 days.