Detailed Guide to Softwood Cutting Propagation of Norway Spruce

Norway spruce (Picea abies) is a superior tree species introduced to China from Northern Europe. The tree grows fast. With a straight trunk, wide adaptability, and especially strong cold resistance, it has not only become an excellent timber species, but also an ornamental species for urban landscaping due to its attractive tree shape and dense, evergreen branches. Because seedlings are raised directly from introduced seeds, growth at the seedling stage is slow, and it takes 5 years before seedlings can leave the nursery; importing seeds also requires a large amount of foreign currency, so development has been very slow. In order to accelerate the promotion of this tree species and meet the needs of rapidly developing forestry construction and urban and rural landscaping, we conducted softwood cutting propagation trials. The trial results showed a rooting rate of 77.5%, an average of 5.6 roots per plant, and a survival rate of 85% for transplanted seedlings. Cutting propagation can not only preserve the superior characteristics of the mother tree, but also allow seedlings to leave the nursery and be used for afforestation 2 years earlier.

I. Collection of Cutting Material

In stands under 10 years old, select superior mother trees with straight trunks and dense crowns, and collect current-year semi-lignified softwood shoots as cutting material. The cutting material is required to be robust in growth, free of pests and diseases, and free of mechanical wounds. It is best to collect and insert cuttings immediately. If the cutting collection stand is far from the cutting site, collection may be done 1-2 days before insertion, but during transport, care must be taken to maintain moisture; the base can be soaked with a high-concentration moisture absorbent to retain water.

II. Cutting Bed Setup

The cutting bed uses a cantilever rotating full-light automatic misting system. The cutting bed is set up in a place in the nursery close to a water source. According to the requirements of the misting system, a circular cutting bed with a diameter of 13 m and a height of 50 cm is built accordingly, with the perimeter built of brick and cement, and drainage holes left at the base every 1.5-2.0 m. First, a layer of large cobblestones 15-20 cm thick is laid on the bed, covered with a filter layer composed of a layer of small stones about 10 cm thick, and on top of the filter layer a layer of clean river sand 20 cm thick is placed as the cutting medium.

III. Sterilization of the Cutting Bed

In order to prevent the cuttings from being harmed by fungi and bacteria and affecting rooting and survival, the cutting medium must be sterilized before insertion. First, thoroughly rinse the bed surface with clean water, then spray it with a 0.5% potassium permanganate solution at a rate of 2500-3000 ml per sq m; a 500-fold dilution of carbendazim may also be used for spraying.

IV. Cutting Preparation and Insertion

The insertion time is around June 20. Cut the Norway spruce cutting material into cuttings 10 x 12 cm long with terminal buds, and remove thin, weak, dry, and poorly developed branches. To improve the survival rate of cuttings, after cutting, bundle every 50 cuttings together and soak the basal 2-3 cm in a 1000 ppm indolebutyric acid solution for 30-50 minutes. Insert cuttings before 10 a.m. and after 4 p.m. on the same day, with an insertion depth of 3.5 cm and a spacing of 3 x 5 cm (666 cuttings per sq m). After insertion, press lightly and water immediately as each cutting is inserted, so that the cuttings are in close contact with the cutting medium.

V. Post-Insertion Management

1. Sterilization and disease prevention. Once the cutting bed is fully planted, immediately spray a 500-fold dilution of carbendazim solution over the entire area for sterilization, at a rate of 1000 ml per sq m. After that, apply the chemical once every 10 days, and add one additional spray after rain. Spraying is done in the evening after the misting has been stopped.

2. Water management. Water management is the key to whether cuttings survive. After insertion, start the automatic intermittent misting system, and the misting interval and misting duration must be strictly controlled. Each misting duration should be the time for the boom to rotate 2 revolutions. As for the interval, during the first 20 days after insertion, on sunny days from 10 a.m. to 5 p.m., mist once every 2-3 minutes, and before 10 a.m. and after 5 p.m. reduce the misting frequency to once every 10-15 minutes. From 41-60 days and after 60 days, the misting frequency is again correspondingly reduced to once every 6-7 minutes, 20-30 minutes, and 10-15 minutes, 40-60 minutes respectively. On cloudy days, the misting frequency should be reduced, and no misting is done at night.

3. Foliar fertilization. Fertilization can supply nutrients to the cuttings and improve cutting survival. From 20 days after insertion to late September, spray a mixture of 0.2% urea and 0.3% monopotassium phosphate once every 7-10 days, with a liquid volume of 0.5 kg per sq m. Foliar fertilization is carried out in the evening after the misting has been stopped.

VI. Transplanting and Bed Transfer

In order to accelerate seedling growth, the rooted 1-year-old seedlings from cuttings must be transplanted to ordinary nursery land and cultivated for 2 years. If cuttings are inserted in late June, the surviving seedlings should be lifted from the cutting bed at the end of October, and seedlings with poorly developed root systems should be removed. After bundling them 60 plants per bundle, store them in sand for overwintering. In the following spring, transplant them using the double-ridge planting method. Water thoroughly immediately after ridging; other seedling-stage management measures are the same as for field-grown seedling transplants.