How to cultivate and propagate zinnias properly? A detailed guide to the methods
The side branches of the zinnia fork in a branching pattern. It blooms in summer and autumn, with a solitary flower head at the top of each branch, a flower diameter of about 10 cm, petals in a variety of colors, a long flowering period, and highly varied flower forms, essentially all of them being double-flowered types.
It is robust, tolerant of drought, fond of sunlight, and prefers fertile, deep soil. It dislikes extreme summer heat. It grows poorly in summer rainy weather with poor drainage. It is the national flower of the United Arab Emirates. With large, brightly colored flowers, early blooming, a long flowering period, and an attractive plant shape, it is a common material for flower beds and flower borders, and dwarf varieties can be grown in pots. Tall varieties are suitable for cut flower production.
The zinnia is native to Mexico, the United States, and South America. Plant height varies markedly with variety, generally 50-90 cm, while dwarf types are only 20-30 cm. The flower head is solitary at the branch tip, and the receptacle is raised and cylindrical. The flower diameter is 5-15 cm, and the ray florets come in colors including white, yellow, red, pink, purple, and bicolor, among others. Flower forms are divided into single and double types. The flowering period is June to October.
The zinnia has strong growth vigor and prefers a warm, dry environment with ample sunlight, though it can also tolerate partial shade. The optimum growth temperature is 20-25°C, and it does not tolerate extreme summer heat; when the temperature is above 35°C, its growth is noticeably weakened, it blooms sparsely, and the flowers are smaller. It is a short-day plant: under long days (14 hours of light per day), plant height increases and there are more ray florets; under short days (9 hours of light per day), the ray florets become smaller and the tubular florets increase in number. It is highly adaptable and not particular about soil, but grows best in deep, well-drained fertile soil. In summers with abundant rain or when the soil drainage is poor, the plants become spindly and the flowers become smaller; continuous cropping should be avoided.
The zinnia is mainly propagated by seed, and can also be propagated by cuttings. Seed propagation is best done by spring sowing, generally in mid-to-late April, with an optimum germination temperature of 15-20°C. Its seeds are photophobic, so after sowing they should be covered with soil, watered, and kept moist; they sprout and emerge in about 1 week. The germination rate is generally around 60%. From Xiaoman to the summer solstice, in combination with pinching and pruning, select vigorous branches and cut a 10-15 cm section of young shoot as a cutting, remove the lower leaves, keep the two upper leaves, insert it into fine river sand, spray water frequently, provide appropriate shade, and it will root in about 2 weeks.
After the plants are established and survive, fertilization during the seedling-growing stage need not be too frequent; generally apply a liquid fertilizer once a month. As the flowering period approaches, more topdressing can be applied, with a liquid fertilizer every 5-7 days until the flowers are in full bloom. When the seedlings reach 10 cm in height, keep 2 pairs of leaves and pinch off the growing tip to encourage the development of side branches. When the side branches grow to 2-3 pairs of leaves, keep 2 pairs of leaves and pinch again a second time. Doing this makes the plant shape fuller and the flowering more abundant. After spring sowing, it can bloom after 70 days. The zinnia blooms at the branch tips, so when the flowers fade, promptly cut off the spent flowers from the base of the flower stem while leaving 2 pairs of leaves, so as to induce new shoots from the leaf axils at the cut. After pruning, water frequently and apply topdressing 2-3 times, which can extend the flowering period to before the first frost. The first batch of seeds that matures before the rainy season is of better quality and should be harvested and saved for seed in good time.
The zinnia is an important annual herbaceous flower and likes a sunny, warm climate. It is drought-tolerant and slightly tolerant of high temperatures. It requires loose, fertile, well-drained soil.
Propagation is mainly by sowing. Sow in the open field in April; under a temperature of 20-25°C, sprouts can emerge in about a week, and when the seedlings are 5-10 cm tall, transplant once with a plant spacing of 10 cm.
The planting site must have good drainage. Because the zinnia has relatively few lateral roots, it should be planted out in good time and with soil attached. The planting distance is 30 cm for dwarf varieties and 50 cm for tall-stemmed varieties. After planting, water thoroughly. Apply topdressing once a month until the plants cover the ground. When the seedlings reach 20 cm in height, begin pinching, doing it 1-2 times to promote branching and increase the number of flowers. Do a good job of intertillage, weeding, and loosening the soil. Spent flowers should be cut off promptly, which helps them sprout and bloom again.