Hydrangea Planting Methods and Key Technical Points
Hydrangea, also known as eight-immortals flower, purple sun flower, seven-change flower, powder-ball flower, foreign hydrangea, etc., is native to the Sichuan area of China and Japan. It is a deciduous shrub of the genus Hydrangea (scientific name: Hydrangea macrophylla) in the family Saxifragaceae, with a plant height of 0.5-1 m. The leaves are elliptical or obovate, with blunt teeth along the edges. The corymb is terminal and spherical. The flowers are almost entirely sterile flowers; the so-called "flower" is merely the sepals.
Propagation Methods
Cuttings, division, layering and grafting are commonly used for propagation, with cuttings being the main method. During the plum rain season, select robust young shoots from a young mother plant as cuttings. The base of the cutting needs to have a node and be dipped in mud slurry. The length is about 20 cm, and the lower leaves are removed. The suitable temperature for cuttings is 1 3-18°C. After insertion, shade is needed and moisture should be kept constant. Roots develop in about 15 days to 1 month, and after survival they can be transplanted in the second year. Division propagation is suitable before budding in early spring. Separate the rooted branches from the mother plant and pot them directly. Do not water too much. Maintain them in semi-shade, and after new buds sprout, return to normal care. Layering propagation can be carried out when the buds begin to swell. Growth occurs after 30 days, and in the following spring cut it from the mother plant, transplant with soil, and it can bloom in the same year. Generally, air layering is done in March-April in spring, roots form in June-July, and it can be cut off and planted separately in the same year. For grafting propagation, use seedlings of Viburnum macrocephalum as rootstock and cleft graft in spring; it is easy to survive. Transplanting is suitable after leaf fall or before budding, and the original soil should be kept. The main branches easily produce water sprouts, so after flowering they need proper pruning to shape the tree.
Cultivation Management
The suitable growth temperature for hydrangea is 18-28°C, and the winter temperature should not be lower than 5°C. Flower bud differentiation requires 6-8 weeks at 5-7°C. A temperature of 20°C can promote flowering. After the flowers appear, maintaining 16°C can prolong the viewing period. However, high temperatures make the flowers fade quickly. Hydrangea is a short-day plant. With more than 10 hours of darkness each day, flower buds form in about 45-50 days. Potted hydrangeas commonly use 15-20 cm pots. After budding in spring, potted plants should be watered thoroughly to ensure the leaves do not wilt. During the flowering period in June-July, fertilizer and water should be sufficient, with fertilization once every half month. In ordinary cultivation, avoid direct sunlight, and 60%-70% shade is ideal. When the light is too strong in midsummer, appropriate shading can prolong the viewing period. After flowering, remove the flower stems to encourage new branches.
The soil is best as loose, fertile and well-drained sandy loam. But flower color is affected by soil pH: in acidic soil the flowers are blue, and in alkaline soil they are red. The potting soil should be kept moist, but watering should not be excessive. Especially in the rainy season, pay attention to drainage to prevent waterlogging from causing root rot. In winter, indoor potted plants are better kept slightly dry. If too moist, the leaves rot easily. Repot once every spring. Prune properly to maintain a beautiful plant shape.
Potting and Pruning
(1) In addition to a seedbed made of bricks, for easy movement and management, a foam box can be used as a seedbed. First cut several openings in the bottom of the box, cover the openings with tile pieces, fill in a layer of coarse sand, then put in the growing medium (3 parts sand and 2 parts sterile mountain soil mixed evenly), and level it before inserting cuttings. Cut the cuttings into 10-15 cm sections, remove the lower leaves of the terminal branches, and keep only 2-3 leaves at the top. After cutting, tie the cuttings neatly and level them. In order for the cutting wounds to heal and root early, soak the leveled cuttings in a strong rooting agent (about 0.2 kg of water per packet) for 5-10 minutes before inserting. After inserting, press the soil around the branches firmly with your fingers so that the cuttings are closely combined with the soil. Then water thoroughly once with a watering can. After that, as long as the bed soil is moist, there is no need to water, but frequently mist the cutting leaves and keep the environment around the seedbed moist. If the weather is hot and the sunlight is strong, a shade shed must be built for shading. Under such careful management, in about 25 days the wounds begin to heal and new roots grow from the nodes.
(2) Potting and care. After about 25 days of careful management, the hydrangea has survived and new leaf buds begin to grow upward from the terminal bud. At this time it must be divided and potted for management. The growing medium for cultivating hydrangea uses coniferous soil (relatively high in acid) plus chaff, and a compound fertilizer of nitrogen, phosphorus and potassium (according to the amount of coniferous soil) mixed with the soil, piled and fully fermented for more than half a year. Before use, turn it over and sun-dry it for several days and it can be used. After the seedlings survive and the terminal branch grows to about 10 cm, the first pinching can be carried out to encourage new leaf buds in the lower part; when the several branch buds that later grow reach a certain length, carry out the second pinching and let them grow evenly and lushly. When the main trunk branches are thick, leave only 3-4 branches to grow freely. From potting and survival to the branch-setting period, fertilizer needs to be applied 3-4 times, mainly potassium dihydrogen phosphate.
Pest and Disease Control
The main ones are wilt disease, powdery mildew and leaf spot disease.
Spray with 65% zineb wettable powder at 600 times dilution for control.
Pests include aphids and mirid bugs, which can be killed by spraying with 40% omethoate emulsifiable concentrate at 1500 times dilution.