COLD STORAGE OF STRAWBERRY PLANTS FOR OVERWINTERING IN A DOUBLE CROPPING SYSTEM IN PLASTIC GREENHOUSE

By combining different cultivation systems, year-round strawberry production is pursued in Belgium. In a double-cropping system in plastic greenhouses, the plants need enough chilling between the first crop in autumn and the second crop in spring. On the other hand, the plants should be protected against frost during the winter. By storing the plants in cooling units, temperature can be controlled, and a sufficient amount of chilling units can be obtained without incurring frost damage. Different overwintering techniques were compared. After the first crop in autumn, plants remained in the greenhouse for several weeks, after which the leaves were cut. A part of the plants were kept in the greenhouse the entire winter, while the rest was moved into a wet (0°C) and/or dry (-1.5°C) cooling system, by putting the culture pots in stacked wooden boxes. To prevent dehydration in the dry cooling system, the stacked boxes are wrapped in plastic foil. The top of the upper box was covered with a plastic foil. Dehydration can also be prevented by using plastic bags inside the box. When wrapping plastic around the boxes, the pallet gaps can be cut open to create cold air flow between the boxes. A quick decrease in temperature inside the boxes is crucial for decreasing plant respiration and obtaining successful preservation of the plants. Results show that cooling of the plants can be successful when certain requirements are met. Plants need a sufficient amount of chilling units before cooling in order to prevent excessive respiration and consequently an inhibition of a rapid temperature decrease. Both dry and wet cooling systems can be successful. Plastic top covers are necessary to prevent dehydration in a dry cooling system each time there is a cold air flow present above the box. The temperature decrease can be influenced positively by opening the pallet gaps. The second crop is delayed by cooling compared to overwintering in the greenhouse.