How to Grow Hydrangeas? A Detailed Guide to Hydrangea Cultivation Methods
The correct name of the hydrangea is hoya, also known as eight immortals flower, purple sun flower, seven transformations, foreign hydrangea, and pink cluster flower. It originated in the Sichuan area of China and Japan. It is a deciduous shrub of the genus Hydrangea in the family Hydrangeaceae, order Cornales. Its flowers are almost entirely sterile, and the so-called “flower” is merely the sepals. China cultivated the eight immortals flower quite early; hydrangeas were planted in the Jiangnan gardens built during the Ming and Qing dynasties. Parks built in the early 20th century also could not do without hydrangea plantings. Modern parks and scenic areas plant them in large masses to form landscapes. Artificially bred hydrangeas have large flowers and vivid colors, with flower colors including blue, white, purple-red, pink, and peach red. It is a common ornamental flowering shrub.
Growth Habits of Hydrangeas
We must first understand the growth habits of hydrangeas in order to master hydrangea cultivation methods in a targeted way. Hydrangeas originated in China's Yangtze River basin and prefer warm, humid, and semi-shaded environments. They fear both drought and waterlogging, are not cold-tolerant, and in cold regions the aboveground parts die in winter, only sprouting new shoots again the following spring. Hydrangeas like fertile, moist, well-drained light loam and have strong adaptability. The acidity or alkalinity of the soil has a major effect on hydrangea flower color: in acidic soil they are mostly blue, and in alkaline soil they are mostly red.
Propagation Methods for Hydrangeas
Cuttings, division, layering, and grafting are commonly used for propagation, with cuttings being the main method. During the plum rain period, select robust young shoots from a young mother plant as cuttings; the base of the cutting must include a node and be dipped in mud slurry. The cuttings should be about 20 cm long, with the lower leaves removed. The suitable temperature for cuttings is 13-18°C. After inserting them, shade is needed and moisture should be maintained regularly. Roots develop in about 15 days to 1 month, and after surviving they can be transplanted in the second year. Division propagation is best carried out in early spring before budding. Separate rooted branches from the mother plant and pot them directly; do not water too much, keep them in semi-shade, and after new buds sprout, switch to normal care. Layering propagation can be done when buds begin to swell; growth occurs after 30 days, and the following spring it can be cut from the mother plant, transplanted with soil, and it may bloom that 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 that same year. For grafting propagation, use seedlings of Viburnum macrocephalum as rootstock and do cleft grafting in spring, which roots easily. Transplanting is best done after leaf fall or before budding, and the root ball must be kept intact. The main branches easily send out vigorous water shoots, so after flowering they should be pruned appropriately to shape the tree.
Cultivation and Management of Hydrangeas
The suitable growth temperature for hydrangeas 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, and after flowers appear, maintaining 16°C can prolong the viewing period. However, high temperatures make the flowers fade quickly. Hydrangeas are short-day plants; with more than 10 hours of darkness per day, flower buds form in about 45-50 days. Potted hydrangeas commonly use 15-20 cm pots. After potted plants sprout in spring, pay attention to watering thoroughly to ensure the leaves do not wilt. During the flowering period in June-July, fertilizer and water must be sufficient, with fertilizer applied once every half month. In ordinary cultivation, avoid direct sunlight, with 60%-70% shade being ideal. When summer sunlight is too strong, appropriate shading can prolong the viewing period. After flowering, remove the flower stems to encourage new branches.
The soil is best as loose, fertile, well-drained sandy loam. However, flower color is affected by soil acidity and alkalinity: acidic soil produces blue flowers, and alkaline soil produces red flowers. The potting soil should be kept moist, but watering should not be excessive. Especially in the rainy season, pay attention to drainage to prevent root rot caused by waterlogging. In winter, indoor potted plants are better kept slightly dry. If too humid, the leaves rot easily. Repot once every spring. Prune appropriately to maintain a beautiful plant shape.
Potting and Pruning Hydrangeas
Hydrangea propagation is suitable in spring and autumn, but late spring and early summer (late April to July) are best. At this time, the hydrangea flowering period has basically ended in May, and after removing spent flowers and withered leaves and pruning, new branches and leaf buds have grown. At this point, the top branch buds can be cut as cuttings. Cuttings can also be taken from late September to October. In early spring, after hydrangeas are pruned and the top buds are taken as cuttings, many new branch leaf buds sprout again. At this time, because the weather turns cooler, it is suitable for cutting propagation.
1. In addition to a seedbed made of bricks, for easier movement and management, a foam box can be used as a seedbed. First cut several openings in the bottom of the box, then cover the openings with tile pieces, fill in a layer of coarse sand, and then add culture soil (mix 3 parts sand and 2 parts sterile mountain soil evenly), and level it before inserting cuttings. Cut the cuttings into 10-15 cm sections, remove the lower leaves of the terminal shoots, and keep only 2-3 leaves at the top. After cutting, tie the cuttings neatly and level them. To help the cutting wounds heal and root early, soak the leveled cuttings in a strong rooting agent (about one packet diluted in 0.2 kg water) for 5-10 minutes before inserting. After inserting, press the soil around the stems firmly with your fingers so the cuttings and soil are tightly combined. 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 mist the cutting leaves frequently and keep the environment around the seedbed moist. If the weather is hot and sunlight is strong, a shade shed must be built for shading. With such careful management, in about 25 days the wounds begin to heal and new roots grow from the nodes.
2. Potting and cultivation care: After about 25 days of careful management, the hydrangeas have survived and new leaf buds begin to grow upward from the top buds. At this time, they must be separately planted and potted for management. The culture soil for cultivating hydrangeas 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 evenly with soil, piled and fully fermented for more than half a year. Before use, turn it over and air-dry it for several days, and then it can be used. After the seedlings survive and the terminal shoots grow to about 10 cm, the first pinching can be done to encourage new leaf buds to sprout from the lower part. When the several branch buds that grow later reach a certain length, do a second pinching and let them grow evenly and vigorously. When the main stem and branches are thick and strong, leave only 3-4 branches and let them grow. From potting survival to branch selection, fertilizer needs to be applied 3-4 times, mainly potassium dihydrogen phosphate.