Plastic greenhouses, also known as cold frames, are widely used in northern regions to extend the growing season for crops like tomatoes. These structures are typically covered with single-layer plastic films, which provide limited insulation compared to solar greenhouses. As a result, they are mainly used during spring and autumn when frost is still a concern but extreme cold has not yet set in. In early spring, Tomato planting in greenhouses can be delayed by about a month compared to open fields, while in the Yangtze River region, winter tomato production is possible using small plastic sheds covered with straw.
In spring, plastic greenhouses help create a more favorable environment for tomato growth when outdoor temperatures remain too low for direct planting. Seedlings are usually sown between mid-January and early February, with a seedling age of 55 to 70 days before transplanting. During this period, especially in areas with poor night-time insulation, it's crucial to maintain proper temperatures to avoid issues like flower malformation or leaf drop due to cold stress. After transplanting, careful attention must be paid to frost protection and timely pollination and fruit care as temperatures gradually rise. Proper ventilation and insect netting should be introduced as conditions improve, and water and fertilizer management should be intensified during the fruit development stage to ensure high-quality harvests.
In the fall, plastic greenhouses play a vital role in supplying tomatoes from mid-September to mid-November in northern areas, helping to meet market demand during the off-season. Sowing typically occurs between late June and mid-July, either through direct seeding or transplanting. However, midsummer planting presents challenges such as high temperatures, strong sunlight, and heavy rains, increasing the risk of virus diseases. Earlier sowing increases disease risk, while later sowing shortens the growing period and reduces yield. To mitigate these issues, shading, temperature control, and rain protection are essential. Seedlings should be kept for about 20 days to avoid overgrowth. The ideal time for fall tomato production is between early September and early October. Flower pruning should occur by mid-September, and when nighttime temperatures drop below 14°C, the greenhouse should be sealed for warmth, while daytime ventilation is still necessary. By mid-October, nighttime temperatures drop rapidly, so additional heating may be required to prevent frost damage. Greenhouses should be closed to promote fruit ripening, and all unripe fruits should be harvested and stored properly before the first major cold spell in late October or early November.
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