Detailed Explanation of Key Points for Greenhouse Strawberry Cultivation Techniques
1. Field Preparation
?? (1) Field Selection Select a field that has not grown strawberries for many years as the production field for greenhouse strawberries.
?? (2) Base Fertilizer Apply sufficient organic base fertilizer to the field. About one month before planting, generally apply 1500-2000 kg of fully decomposed organic fertilizer per 667 sq m as base fertilizer, and plow and harrow multiple times.
(3) Bed Making About 10 days before planting, choose sunny weather and make the beds when the soil has good workability. Before building, additionally apply 50 kg of imported NPK compound fertilizer and 50 kg of superphosphate as surface fertilizer, and apply 10 kg of phoxim granules per 667 sq m to control underground pests such as white grubs. The beds run north-south (parallel to the greenhouse direction). Each greenhouse has 7 beds: the middle 5 beds each have a surface width of 40-45 cm, with 2 rows planted per bed; the 2 beds on the sides each have a surface width of 15-20 cm, with each ridge height of 30-35 cm and the bed furrow depth of about 30-35 cm, with 1 row planted per bed.
2. Planting
(1) Planting Time Mid-September is the suitable period, and it should not be later than early October at the latest.
(2) Seedling Lifting Water the nursery thoroughly one day before digging the seedlings to help keep the soil ball intact and minimize root damage. Plant in separate greenhouses according to seedling size. If using nutrient pot seedlings, remove the plastic pot by hand during planting, which results in a higher survival rate.
(3) Planting Density For the "Fengxiang" variety under greenhouse cultivation, the plant spacing is about 20 cm, with 1800-2000 plants per greenhouse and 6000-7000 plants per 667 sq m.
(4) Directional Planting For ease of management, "directional planting" is adopted, which can also reduce disease and improve fruit quality. The middle 5 beds are planted with 2 rows each, planted as close to both sides as possible (with row spacing controlled at about 30 cm), and the seedling crown of the strawberry plant should be clearly oriented with the curved back facing the outer side of the bed. The 2 beds on both sides of the greenhouse are planted with a single row.
(5) Planting Depth The planting depth must be moderate. The base of the new stem must be buried in the soil to promote new root development, but the heart of the seedling (the stipule part of the outer leaves) must not be buried in the soil. Pay special attention that weak and small seedlings may not survive if planted, otherwise it easily leads to seedling death.
3. Management After Planting Water immediately after planting to stabilize the roots. They will survive in about 10 days. Along with weeding, loosen the soil between plants and earth up the roots. Regularly remove dead, old, and diseased leaves, and promptly fill in missing plants.
(1) Laying Black Plastic Mulch Laying black plastic mulch can maintain soil moisture, suppress weed growth, lower the air temperature inside the greenhouse, isolate strawberry fruits from contact with the soil to reduce disease, and keep the fruits brightly colored, clean, and hygienic. The black plastic mulch is generally laid in mid-to-late October, when the strawberry plants have basically all survived and the work of weeding, loosening soil, earthing up roots, and filling in missing plants has been initially completed. The laying method is to cover the black plastic mulch over the plants on the bed surface, feel for the location of the seedlings, tear a small hole in the mulch, and then carefully pull out the leaves. Be sure to expose the central leaves of the seedling, and press the surrounding old leaves on the mulch over the edges of the holes so that they cling tightly to the ground.
(2) Plastic Film Covering After covering the greenhouse with plastic film, insulation begins. In the Jinshan area, film covering for insulation generally begins from late October to early November. When the temperature continues to drop below 5°C at night, an inner greenhouse frame should be added inside the greenhouse. When the minimum nighttime temperature further drops below 0°C, a small tunnel should be added over the strawberry beds.
(3) Temperature and Humidity Regulation Strawberries have different temperature requirements at different stages of growth and development, and these should be met as much as possible after the greenhouse is warmed. Because greenhouse-cultivated strawberries bloom and bear fruit continuously and in overlapping cycles, after bud emergence, generally maintain 24°C-28°C during the day and 6°C-8°C at night. Temperatures above 30°C or below 5°C are not conducive to strawberry flowering and fruiting. The air humidity inside the greenhouse is very high, especially from early morning to mid-morning or during rainy weather, when relative humidity can reach 95-100%, which hinders pollination, easily breeds disease, and causes severe gray mold rot. Therefore, in addition to covering the beds with black plastic mulch, straw should also be spread on the bottom of the furrows to prevent water evaporation. On sunny days around 9 o'clock, ventilation should be carried out on the leeward side with a single-sided skirt to reduce the humidity inside the greenhouse to below 75%.
(4) Plant Management After insulation in the greenhouse, strawberry plants grow faster and sprout a large number of tillers and runners, which should be removed promptly. This can increase the leaf area of the main stem, promote timely emergence of the terminal flower buds, and produce robust terminal inflorescences, leading to early flowering and good fruiting. Generally, each strawberry plant should retain at most 1-2 relatively robust tillers. Promptly remove old, declining, and diseased leaves.
(5) Gibberellin Treatment Generally carried out about 7 days after covering the greenhouse with plastic film (under sunny conditions). The purpose of spraying gibberellin is mainly to address phenomena such as weak growth vigor of strawberry plants, prostrate and dwarfed growth, smaller leaves, short petioles, and short inflorescence stalks. Taking the "Fengxiang" variety as an example, the concentration is generally controlled at about 7 PPM, and the dosage is 10-12 kg of solution per standard greenhouse. Spraying should be done on sunny days. If the plant growth condition does not improve significantly after spraying, spray once more during the bud emergence stage.
(6) Bud Thinning and Flower Thinning Strawberries have cymose inflorescences with many flowers. The development and opening of these flowers consumes a lot of nutrients, especially the higher-order flowers. Even if they set fruit, the fruit is small and poor in quality with no economic value, so buds and flowers should be thinned as early as possible. Generally, this work can be carried out after flowering. Mainly retain the 1st, 2nd, and 3rd order flowers, and first remove the 4th and 5th order flower buds, black flowers (frost-damaged flowers), and severely deformed fruits. Generally, each strawberry plant retains 6-7 fruits on the terminal inflorescence, and the number of fruits retained on subsequent inflorescences depends on growth and harvest conditions. In total, no more than 15 fruits of varying sizes should be borne at the same time. Along with bud and flower thinning, promptly remove old leaves and inflorescence stalks that have finished fruiting.
(7) Top Dressing Greenhouse strawberry top dressing is generally applied 2-3 times from after planting and survival to before and after covering with black plastic mulch. Each greenhouse (180 sq m) uses 1-1.5 kg of urea dissolved in about 500 kg of water for irrigation application each time. Thereafter, top dressing is mostly foliar feeding based on seedling vigor, spraying 20 kg of 0.5% concentration urea per 667 sq m.
(8) Prevention of Black Flowers Black flowers form after low-temperature frost damage. If flower buds 7-8 days before flowering encounter a low temperature of minus 2°C, the stamens can be damaged. If the pistils from 3 days before flowering to one week after flowering encounter a low temperature of minus 2°C, they will also be frost-damaged and form black flowers. Therefore, before severe cold arrives, prepare the inner layer greenhouse frame and small tunnels to strengthen insulation. Keeping the minimum nighttime temperature inside the greenhouse at 3°C-5°C can effectively reduce the formation of black flowers.
(9) Prevention of Deformed Fruits The occurrence of deformed fruits is mainly caused by multiple factors such as temperature, humidity, wind, and improper pesticide spraying. In general, it is caused by poor pollination. Therefore, by strengthening insulation and reducing humidity in the greenhouse in winter, avoiding pesticide spraying as much as possible when the 1st-2nd order flowers of each inflorescence are in full bloom, and keeping bees inside the greenhouse for pollination, the formation of deformed fruits can be significantly reduced.