What are the techniques for growing strawberries in greenhouses?
Strawberries have long been deeply loved for their sweet-and-sour taste, fresh fragrance and rich nutritional value. Some people group them together with mangosteen and blueberries under the name “queen of fruits”, which further highlights the place strawberries hold in people's hearts. Nowadays, in order to achieve off-season cultivation of strawberries and obtain greater economic benefits, strawberry cultivation mostly uses plastic film-covered small arched tunnels for planting. In order to bring them to market early to meet market demand, the key lies in winter management, and the main thing is to grasp the following five technical points.
1. Cover the tunnel and keep it warm at the right time. Generally, when the temperature drops below 5°C, a semicircular small arched tunnel should promptly be set up over the strawberry cultivation beds, covered with colorless plastic film. At the beginning of covering the tunnel, attention should be paid to ventilation to prevent the temperature inside the tunnel from exceeding 30°C, especially around noon on clear, cloudless days with strong sunlight, when high temperatures scorching the seedlings must be prevented even more. In addition, when the minimum temperature inside the tunnel is around 5°C, paper quilts or straw mats should be laid over the tunnel film at night to keep warm, and removed promptly after sunrise during the day to increase sunlight exposure and raise the temperature inside the tunnel, carefully preventing cold damage or root rot. Once the coldest days of winter arrive, if the maximum temperature inside the tunnel is below 10°C, the insulating coverings should also not be removed during the day, so as to help the strawberries overwinter safely. After the “fifth nine-day period” and “sixth nine-day period”, when the outside temperature steadily remains above 0°C, the paper quilts or straw mats can be removed after sunrise during the day, but they must be put back in place before sunset in the evening to maintain a relatively high temperature inside the arched tunnel. When the temperature inside the small arched tunnel also steadily remains above 5°C at night, the coverings can be removed, and attention should be paid to weather changes at all times, with timely ventilation to prevent high-temperature damage.
2. Prevent early buds and early flowers. In the process of greenhouse strawberry production, plants are prone to showing buds early and blooming early. If this phenomenon occurs too much, it will seriously affect the yield and quality of strawberries. The occurrence of early buds and early flowers in greenhouse strawberries is related to the following factors. First, it is related to varietal characteristics. Varieties whose flower buds differentiate easily and whose dormancy is relatively shallow, such as Lihong and Qiuxiang, need only about 50 hours of dormancy, require less low temperature during the dormancy period, and are prone to early buds. Second, it is related to premature flower bud differentiation caused by fertilizer and temporary planting. On the one hand, during seedling raising and before flower bud differentiation, if nitrogen uptake is relatively low, strawberry flower bud differentiation often occurs earlier; on the other hand, if temporary planting is done too late, the temporarily planted seedlings are too small, or aged seedlings form, or the soil in the temporary planting bed is too dry or too wet, or fertilizer is insufficient, all of these can cause strawberry flower buds to differentiate prematurely. All of these will cause early buds and early flowers in strawberries after planting. To prevent early buds and early flowers in strawberries, the following points should be achieved in production: First, choose suitable varieties. For greenhouse cultivation, varieties with relatively shallow dormancy should be chosen. If varieties with relatively strong dormancy are chosen, heat-preserving covering should not be done too early. Second, during the seedling raising process, fertilize reasonably, strengthen management and cultivate strong seedlings. By removing old leaves, removing inflorescences, straightening runners, spraying gibberellin and other measures, strengthen the management of the mother plants and produce high-quality strong seedlings. Third, pay attention to temperature control after covering the tunnel. The temperature inside the tunnel should be controlled below 25°C during the day and above 0°C at night. In severe winter, through measures such as putting small tunnels inside the greenhouse, thickening coverings and setting up windbreaks, ensure normal strawberry development. For plants that have already developed early buds and early flowers, remove the flower buds promptly, strengthen fertilizer and water management, and promote axillary buds to bloom and bear fruit, so as to reduce losses.
3. Strengthen fertilizer and water management. Greenhouse strawberries have a long fruiting period, so on the basis of heavy application of base fertilizer, reasonable topdressing should be carried out to meet their nutritional requirements. Topdressing follows the principle of “small amounts, many times”. From covering the tunnel to bud emergence, shallow watering with fertilizer can be done about once every 10 days, applying 10 kg of urea, 5-8 kg each of superphosphate and potassium chloride per mu each time. In addition, in the middle and late stages, combined with pesticide spraying, organic nutrient solutions such as multi-element micro-fertilizer or Zhibaosu can be sprayed on the leaves to increase strawberry fruit weight and sugar content. When the temperature inside the greenhouse is too high and soil moisture evaporation is large, irrigation should be done in time. In the early stage, when the outside temperature is high, irrigation should be carried out in the evening; in the later stage, when temperatures inside and outside the greenhouse are both relatively low, irrigation should be carried out in the morning. After irrigation, first raise the greenhouse temperature, then increase ventilation to lower humidity. Do not water too frequently, and each watering should soak thoroughly. Stop watering 1 week before flowering, and 15 days after flowering, water once in combination with fertilization.
4. Prevent deformed fruit. Mixing some varieties with a large amount of pollen into the main cultivated varieties is an effective measure to prevent deformed fruit in greenhouse strawberries. The local main cultivated variety is Baojiaozaosheng, and the pollinating varieties are Chunxiang, Fengxiang and others, generally planted at 5%-10%. Pesticides must not be sprayed during the strawberry flowering period, to prevent the pollen germination rate from decreasing, affecting fertilization and producing deformed fruit. Diseases can be controlled with medication before strawberry flowering, and after flowering, diseased plants should be promptly pulled out and diseased leaves and inflorescences removed to control the spread of disease. When soil moisture is insufficient, timely dark irrigation under the plastic film between ridges should be carried out. When fertilizer is lacking, apply 15 kg of 45% ternary compound fertilizer per mu in combination with watering, and do not apply ammonium bicarbonate. It is better to dilute the fertilizer with water and then apply it by punching holes, because in this way water can promote fertilizer and meet the needs of normal flowering and fruiting of strawberries. When each batch of flower buds forms in greenhouse strawberries, place bees inside the tunnel, stocking 5,000 bees per standard tunnel, so that the pollination rate can reach 100%. The times for placing bees are 8-9 a.m. and 3-4 p.m.
5. Prevent and control diseases and insect pests. When using small arched tunnels to cultivate strawberries, because the small environment inside the tunnel has high temperature and high humidity, it is very easy for diseases such as powdery mildew and gray mold, as well as underground pests, to harm strawberry plants. For insect pests, before planting, 25% phoxim can be mixed with water or fine soil and scattered into the soil, or trichlorfon powder can be scattered into the soil for control. For diseases, after mulching with film, promptly spray 40% thiophanate-methyl at 300-400 times dilution or Bordeaux mixture at 240 times dilution.
The above are the main technical points for growing strawberries in greenhouses. As severe winter is approaching, strawberry growers might as well give it a try. Perhaps next year's harvest will reach an even higher level, so act quickly!