Key points of boxwood cutting propagation technology, suitable for northern regions

Boxwood is an evergreen tree species from the south, belonging to the Buxaceae family, genus Buxus. For many years, because of its many advantages such as low, compact growth, dense leaves, beautiful shape and evergreen foliage, it has been deeply loved by people and widely used in hedges and topiary design in landscaping. It is one of the tree species with the largest usage and the widest application in northern landscaping, but due to the influence of climate and other factors, raising seedlings in the north has always been relatively difficult. Greening seedlings in the north can only be transported over long distances from the south, which not only increases costs but also results in a low seedling survival rate. In response, we carefully summarized the experience and lessons in boxwood cutting propagation, changed winter cuttings to summer cuttings, changed soil substrate to stone substrate, changed old branches to young branches, and changed natural conditions to protected conditions. After many trials, we summarized a set of boxwood cutting propagation techniques suitable for northern regions, and achieved success through large-scale promotion. Not only is the survival rate as high as over 85%, but it is also easy to operate and produces seedlings quickly, ending the history of difficult boxwood propagation in northern regions. Last year alone, we used this technique to propagate 400,000 cuttings. The specific operation methods and technical key points are as follows:

I. Requirements for the cutting bed

1. The cutting bed should be selected on a plot with good ventilation and drainage. Build the bed with a bed surface of 1-1.2 m and an operation strip of 0.5-0.6 m. The surroundings of the bed should be enclosed with upright bricks. The bed surface should be deeply turned and leveled to prepare for filling the substrate, and the operation strip should be hardened with bricks.

2. Substrate: stone powder with good water retention and air permeability should be selected, and clean fine river sand can also be used as a substitute. The substrate thickness is generally 4-5 cm, and a 2 cm thick layer of coarse sand should be added at the lower layer.

3. Shading: A solar greenhouse with the film removed and covered with a 65% shading shade net can be used. If there is no solar greenhouse, bamboo poles or steel frames can also be used to build a shed frame, generally 20-30 m long from north to south and 6-8 m wide from east to west. The shed frame must be sturdy to prepare for covering with film in winter.

4. Micro-sprinkling: Because leafy cuttings are taken during the growing season, micro-sprinkling is the main measure for cooling and increasing humidity. The sprinkler heads should be evenly distributed according to their spraying diameter, and there should be no dead corners on the bed surface. It is best to use a fully automatic intermittent spray device; if conditions are poor, manual control is also acceptable.

II. Requirements for cuttings

1. Cutting time: Cuttings can be taken from mid-May to early August, and it is best before the peak of new shoot growth begins and after it ends.

2. Mother plants and cuttings: Cuttings are the internal factor affecting cutting survival. According to experience, it is better to select mother plants that are younger in tree age (1-5 years old), growing vigorously, and free of pests and diseases. For cuttings, choose annual semi-lignified clustered branches or single branches and biennial vigorous clustered branches; generally do not use old branches more than three years old.

3. Management of cuttings: Branches should be collected before 10 a.m. and after 4 p.m. After collection, trim and insert them in a cool place to reduce water loss. Remove branches and leaves from 4-5 cm above the base of the cutting, leave 2-3 leafy small branches at the upper part, and cut the tips of the leafy small branches to 5-6 cm. Leaving a certain number of leaves on the cutting is beneficial for rooting. Because boxwood belongs to the callus rooting type, the wounds caused by removing branches at the base are also beneficial for rooting. After treating the branches, bundle them in groups of 30-50 (with the bases aligned) and soak them in a container holding 2-3 cm of clean water until use.

III. Cutting

1. The base of the cutting bed should be thoroughly watered, and dry insertion should not be used.

2. Before insertion, treat with hormone, generally dipping the base of the branches quickly in 500 mg/kg naphthaleneacetic acid.

3. The plant and row spacing is generally 4 cm x 4 cm, or 5 cm x 5 cm. Dense insertion at 2 cm x 2 cm is also possible, followed by transplanting after rooting. The insertion depth is preferably 4-5 cm, and after insertion the substrate around the branches should be pressed firm by hand.

IV. Management after cutting

1. Humidity control: Humidity is the key factor affecting cutting survival, including substrate humidity and air humidity. Generally, the substrate moisture content should be maintained at 15%-25%. If the water amount is too large, aeration will decrease and cause branch tip rot. The relative air humidity should preferably be no lower than 70%. Therefore, the micro-sprinkling time should be determined according to the specific cutting time, weather conditions and rooting conditions. During high-temperature periods, the spraying time should be appropriately extended, while in the morning, evening and on cloudy and rainy days, spraying should be reduced or not done as appropriate. Within 1 month after cutting, it is the rooting period and more spraying is needed; after rooting, less spraying is needed. If heavy rain occurs, drainage should also be carried out promptly.

2. Pest and disease control: Because cutting takes place in the high-temperature season and humidity is high, the branches are prone to disease. Carbendazim or chlorothalonil should be sprayed once every 1 week. If there are leaf-eating insects, pesticide should also be applied promptly.

3. If the cuttings are not transplanted in the same year after surviving, foliar fertilization should be carried out once every 15 days, generally spraying 0.3%-0.5% imported urea or compound fertilizer.

4. If transplanted in the same year, the shade net should be gradually removed 2 months after cutting and water control should be used to harden the seedlings, so that the young seedlings gradually adapt to the external environment after planting.