Key Management Points for Greenhouse Grapes in January–March

1. Greenhouse Film Management and Temperature–Humidity Control

1) Installing and sealing the plastic mulch. For single‑layer mulch cultivation, the mulch is typically sealed in mid- to late January; for double‑layer mulch cultivation, it can be sealed from late December to early January. When sealing, first lay the top film, then seal the side films—never seal them simultaneously. For double‑layer mulch systems, it is best to apply the inner film about 15 days after the outer film has been laid.

2) Dormancy-breaking treatment: After removing the plastic cover, apply a 20% calcium cyanamide solution or a 20-fold dilution of Duomeizhi to break dormancy by coating the buds; however, do not apply it to the apical bud. If the shoots become dry within seven days after treatment, spray them with water once to enhance absorption.

3) Temperature and humidity control. After mulching, raise the temperature gradually to ensure that air temperature and soil temperature remain in harmony. Initially, implement low‑temperature management: during the day, maintain the greenhouse temperature at 15–20°C, and at night at 5–10°C. In the second week after covering the greenhouse, increase daytime temperatures to 15–20°C while keeping nighttime temperatures at 7–10°C. By the third week, gradually raise daytime temperatures to 20–25°C and maintain nighttime temperatures at 10–15°C. Following bud break, strictly regulate greenhouse temperatures, with an optimal range of 22–28°C during the day and no lower than 10°C at night; relative humidity inside the greenhouse should be kept between 60% and 70%. During the new shoot growth stage, maintain soil moisture at 70%–80% and air humidity around 70%, with nighttime temperatures not falling below 10°C and daytime temperatures not exceeding 30°C. During the flowering period, keep greenhouse temperatures between 15 and 28°C and relative humidity between 50% and 60%.

4) Greenhouse film management: After bud break, promptly lift the side films for ventilation and cooling when the temperature inside exceeds 32°C; after 3:00 p.m., lower the side films to retain heat once the internal temperature drops below 25°C. When new shoots reach 2 cm in length, apply mulch film across the entire orchard. During the flowering period, open the roof vents for ventilation and cooling when the internal temperature rises above 30°C. If excessive humidity causes fogging inside the greenhouse, ventilate promptly to reduce moisture, thereby preventing high temperature and high humidity from leading to bud rot, flower rot, and the exacerbation of diseases. Before the onset of cold weather, seal the greenhouse early and cover the exterior with insulating materials, or implement warming measures such as fumigation or heating inside the structure to ensure healthy shoot growth, flowering, and fruit set.

2. Fertilizer and Water Management

1) Irrigation: Before mulching, thoroughly irrigate the greenhouse to ensure adequate moisture; this is known as the “mulch‑covering irrigation.” After mulching, irrigate promptly according to soil and air humidity conditions: during the germination stage, maintain a relative soil water holding capacity of 70%–80% and keep indoor air humidity above 90%; during the bud‑break stage, apply a single, uniform irrigation—referred to as the “bud‑break irrigation”—to promote uniform sprouting. Following bud break, irrigate frequently with small amounts based on soil moisture levels; avoid excessive flood irrigation. During the new shoot growth period, water demand is high; maintain soil moisture at 70%–80% and minimize abrupt fluctuations in soil moisture. Ten days before flowering, apply a “flower‑induction irrigation” according to soil moisture conditions, keeping soil moisture at 60%–65% during bloom. Excessive moisture during flowering can lead to significant flower and fruit drop; unless the soil is excessively dry, refrain from watering during this phase.

2) Fertilization.

3. Vine and Fruit Management

1) Bud removal. Primarily, remove secondary buds, weak buds, and buds that are improperly positioned on the fruiting canes. When the buds have developed 2–3 leaves, regardless of whether a cane produces double or multiple buds, retain only one vigorous bud and remove all others. On average, leave one bud every 15–20 cm along the fruiting cane, with 2–5 buds per cane; leave more buds where branches are lacking and fewer where they are abundant, ensuring that each bud eye bears only one shoot. However, in regions prone to early‑spring low temperatures, prolonged rain, and late spring frosts, to safeguard yield, you may also decide whether to keep or remove shoots when they have grown to 4–5 leaves, based on the position of the flower clusters.

2) Pinch and tie the shoots. Determine the number of shoots to retain based on cluster size, leaf size, an appropriate shoot–cluster ratio, and target yield. For clusters averaging over 500 grams or for large‑leaf varieties, typically maintain 2,800–3,000 shoots per mu; for clusters averaging around 500 grams or for medium‑leaf varieties, aim for 3,000–3,500 shoots per mu. Remove any tendrils promptly, and also thin out weak, non‑flowering young shoots and overly dense growth. When new shoots reach 30–40 cm in length, tie them securely as you prune to prevent wind damage.

3) Pinching and cluster thinning. Perform pinching 3–5 days before flowering or when the first flowers appear across the entire vineyard. Typically, leave 5–7 leaves above the flower cluster and pinch; for vigorous vines, retain more leaves. For varieties like Kyoho that are prone to flower and fruit drop, pinch back to 2–4 leaves. On secondary shoots below the flower cluster, remove the terminal leaf and then pinch; on shoots above the flower cluster, leave 1–2 leaves and repeat pinching; retain 1–2 apical secondary shoots and pinch them repeatedly at 3–4 leaves. For developing canes, pinch back to 10–13 leaves, and on the resulting secondary shoots, leave 2–3 leaves and continue pinching. One week before flowering, carry out cluster thinning: remove shoulder clusters and the first and second secondary clusters; for large clusters, shorten the secondary clusters by one‑third to one‑half and trim the tip by one‑fifth to one‑quarter, ensuring a neat, well‑shaped cluster—typically conical in European‑Asian hybrids and cylindrical in European‑American crosses. At the same time, determine the number of clusters based on the leaf‑to‑fruit ratio, cluster size, and desired yield: weak shoots should bear no clusters, medium‑strength shoots one cluster, and vigorous shoots two clusters. In a vineyard yielding 1,500 kg per mu, select and retain 2,000–2,500 flower clusters, depending on cluster size.

4) Seedlessness treatment. Seedlessness is suitable for varieties that set fruit parthenocarpically in large numbers, have poor commercial quality when fruiting naturally, or mature early, such as the Kyoho‑type cultivars Fujiminori, Kyoho, Sōtetsu, Saikinkō, and Kyo‑ya. These varieties require uniformly vigorous growth and well‑developed shoots; flower‑cluster thinning should be carried out 7–10 days before flowering, typically leaving 4–7 cm of the cluster tip. For Kyoho‑type grapes, seedlessness is generally achieved through a two‑step treatment: the first application, 2 days around full bloom, involves immersing or spraying the inflorescence with a solution containing 12.5–25 mg/kg gibberellic acid plus 2–5 mg/kg paclobutrazol; a second application, 10–15 days later, uses 25 mg/kg gibberellic acid. In each treatment, a spreading agent such as Kuairun or Tween 20 should be added at a dilution of 3,000–4,000 times to ensure even coverage of the spray solution.

4. Pest and Disease Control

1) Thoroughly clean the vineyard. For areas that were not cleared in the previous autumn–winter season, or where cleanup was incomplete, remove all weeds, dead branches, old bark, diseased leaves, fallen fruit, and any plastic ties still attached to new shoots on the wires; dispose of these materials by burning or deep burial. During the grape “velvet ball” stage—ideally after the velvet balls turn green—apply a single spray of 3–5°Bé lime–sulfur mixture across the entire orchard to reduce the initial population of pests and pathogens. Ensure this treatment is comprehensive and thorough, covering every surface: the trees, the ground, the support posts, the trellis wires, and the wire itself. For vineyards with a history of complex pest and disease problems, add an additional spray of a mixture consisting of an 80% fungicide diluted 300–500 times, combined with an oil (or diesel) emulsion diluted 200 times.

2) Timely prevention and control at the node level.