Detailed Explanation of Key Techniques for Greenhouse Cultivation of American Blackberry

American blackberry, commonly known as “black strawberry”, is a perennial vine fresh-eating fruit of the genus Rubus in the Rosaceae family. Native to North America, it is a third-generation emerging fruit.

1. Greenhouse structure: The greenhouse faces south, with its length running east-west. The north wall and gable walls are built with adobe bricks, with a wall thickness of 0-8m. The frame uses concrete pillars as uprights and bamboo poles as support frames. The greenhouse is 60m long, 10m wide, and 3m high at the roof. The film used for the greenhouse is anti-drip film.

2. Planting and trellising methods:

(1) Planting. Use north-south row planting, with a plant-to-row spacing of lm×1.6m, that is, 420 plants per 667m2. Planting time is November-December or March-April. Before planting, dig planting trenches 50cm wide and 60cm long according to the plant-to-row spacing, and per 667 square meters apply 4000 tons of high-quality farmyard manure and 50kg of compound fertilizer into the trenches. When planting, select high-quality vigorous seedlings with well-developed roots.

(2) Trellising. Use a hedge-type trellis. After planting, set a concrete pillar every 5m along the planting row, and stretch 2-3 wires on the pillars, with 30-40cm spacing between the wires.

3. Management inside the greenhouse:

(1) Time to cover the greenhouse. Timely covering of the greenhouse for heat preservation is a key technique in blackberry cultivation. When the nighttime field temperature drops to 8.0 degrees C, covering the greenhouse is relatively suitable. At this time, flower buds have already differentiated and the plants have not yet entered dormancy.

(2) Fertilizer, water and humidity management. Before covering the greenhouse, sufficient base fertilizer should be applied: per 667 square meters, apply 3000kg of high-quality farmyard manure, 50% potassium sulfate, and 30kg each of diammonium phosphate containing 47% phosphorus and 19% nitrogen. Topdressing is carried out in 2 applications before flowering and during the fruit enlargement stage, generally using 50-75g of compound fertilizer per plant. Starting 7-10 days before flowering, spray foliar fertilizer once every 10-15 days, in sequence: urea (300x solution), amino acid compound fertilizer (300x solution), photosynthetic micro-fertilizer (500x solution), monopotassium phosphate (300x solution), etc.

Water 3 times in total, respectively after covering the greenhouse, before flowering, and during the fruit enlargement stage. The relative humidity inside the greenhouse should preferably be 70%-80% before flowering; when the temperature is on the low side, water can be sprayed on the branches to promote new shoot growth; during flowering and fruit set, it should preferably be around 60%, which is favorable for pollination and fruit set; after fruit set until the harvest period, it should preferably be 60%-70%. If humidity is too high, ventilate for 1-2 hours every morning to reduce humidity, or add plastic mulch to reduce soil moisture evaporation into the greenhouse.

(3) Temperature regulation. The temperature regulation of blackberry from covering the greenhouse to the end of harvest can be divided into 4 periods:

(1) From covering the greenhouse to the bud break stage, keep the greenhouse closed for 4-5 days after covering, with straw curtains covering day and night; then roll up the straw curtains on the greenhouse at around 8 a.m. each day, and cover them again at 3 p.m.

(2) From budding to before flowering, during this period regulate the daytime temperature inside the greenhouse to no more than 20 degrees C, and keep the nighttime temperature at 4-10 degrees C.

(3) From flowering to before berry enlargement, during this period regulate the daytime temperature inside the greenhouse to 20-26 degrees C, and keep the nighttime temperature at 7-13 degrees C, to favor pollination and increase the fruit set rate;

(4) From berry enlargement to the end of harvest, during this period keep the daytime temperature inside the greenhouse at 25-32 degrees C, and maintain the nighttime temperature at 10-16 degrees C; control the day-night temperature difference above 10 degrees C to favor berry enlargement, coloring, and increased sugar content. During periods (2)-(4), if the temperature inside the greenhouse is too high, open ventilation windows to cool it down; if the temperature drops to the lower limit of the suitable range, promptly close the ventilation windows, etc., and even cover straw curtains. In case of continuous rainy and cloudy days, measures can be taken inside the greenhouse to increase temperature and preserve heat.

(4) Shaping and pruning. After planting, the young seedlings begin to sprout in spring. Keep 3-4 vigorous new shoots at the base and tie them upward to the wires on the pillars, and cut off the remaining new shoots from the stem base, so as to form 3-4 main trunk branches. After covering the greenhouse, similarly keep 2-3 new growing shoots to form 2-3 secondary trunk branches, and cut off the remaining new shoots from the stem base. When the main and secondary trunk branches grow to 60cm, begin to keep secondary shoots to form side branches. When the main and secondary trunk branches grow to lm, top them in time to promote secondary shoot growth. Secondary shoots are generally topped after retaining 4-7 leaves. In late August, cut off some pest-damaged branches, thin and weak branches, and overly dense branches; after covering the greenhouse, cut off dead branches and aged branches on the main and secondary trunk branches from the base. Generally, keep 3-4 main trunk branches and 2-3 secondary trunk branches per plant, retain 4-6 side branches on each main and secondary trunk branch, and retain about 450 buds per plant.

(5) Harvesting. Inside the greenhouse, the temperature is higher in the middle area, so berries ripen earlier, while the temperature is lower in the surrounding 2m area, so berries ripen later. The berry ripening period inside the greenhouse starts in late March and ends in late April, lasting 30-40 days, so harvesting should be done in batches, generally once every 5-6 days.