Overwintering Management Methods and Technical Points for Flowers in Greenhouses

According to observations, during continuous rain and snow, the temperature difference between inside and outside the greenhouse is 2°C—4°C; on clear days, the temperature inside the greenhouse rises quickly and can be 15°C—25°C higher than outside; while in the early morning or late at night, the temperature inside the greenhouse is only 1°C—3°C higher than outside. Therefore, flowers should be managed in plastic greenhouses reasonably according to their different types.

I. Flowers suitable for overwintering in cold rooms

Potted camellias, azaleas, palm grass (Rhapis excelsa), banana shrubs (Michelia figo), and amaryllis (Hippeastrum) in the Yangtze River basin can safely overwinter in a dormant state as long as they are given slight protection during low temperatures. After being moved into the greenhouse, attention should be paid to ventilation and cooling on clear days, and their dormancy must not be broken. Of course, if the purpose is to force flowering, that is a different matter. For cineraria, primroses, calceolaria (Pouch Flower), cyclamen, and calla lilies, the daytime temperature should be kept at 15°C—20°C. If the greenhouse temperature is too high, ventilate; at night, cover for insulation; if the temperature is too low, add heat to keep it around 5°C, and do not let it fall below 0°C.

II. Flowers suitable for overwintering in heated greenhouses

Cacti, bromeliads, marantas (Prayer Plants), crotons (Codiaeum variegatum), Brazilian ironwood (Caesalpinia ferrea), money trees (Pachira aquatica), dragon trees (Dracaena), tropical orchids, and other flowers that prefer high temperatures. First, cover the outside of the greenhouse with insulation material to prevent heat loss at night; this method is extremely effective on clear nights. Second, build a simple greenhouse inside the greenhouse, that is, a double-layer greenhouse. The spacing between the two layers of plastic film is best kept at about 10 cm; the air in between has a lower thermal conductivity, giving a better insulation effect, and the temperature inside the greenhouse is more stable. Third, add heat, using electricity or a boiler for heating; energy consumption is relatively large and the cost is relatively high, so it can be combined with the previous two measures and used for short periods during especially low temperatures and on rainy and snowy days. For such flowers, on clear days, if the greenhouse temperature reaches above 25°C, ventilate as well, to maintain overwintering in dormancy.

In addition, the air humidity inside the greenhouse is high, so special attention should be paid to the prevention and control of fungal diseases such as black spot and powdery mildew. For flowers overwintering in dormancy, stop fertilizing, control watering, and keep them in a semi-arid state to prevent root rot and seedling death. For flowers growing inside the greenhouse, watering should also be moderately controlled, watering when dry and letting them dry out between waterings, and ventilating frequently to keep them growing robustly.