How to Grow Potted Poinsettias? A Detailed Guide to Cultivation Methods

Poinsettia, also known as ivory red, laolai jiao, Christmas flower, and so on, is an evergreen shrub of the genus Euphorbia in the family Euphorbiaceae. It is native to Central America and widely cultivated in tropical and subtropical regions. It is cultivated in the vast majority of provinces, regions, and municipalities in China, and is commonly seen in parks, botanical gardens, and greenhouses for ornamental purposes. Its stems and leaves are used in medicine and have a detumescence effect. Now let us take a look at the cultivation methods for potted poinsettias!

Growth Habits of Poinsettia

Poinsettia is native to the Taxco region of Mexico in Central America, and was introduced to the United States in 1825 by Joel·Poinsett, the first U.S. ambassador to Mexico. It is a short-day plant and prefers warmth. The suitable temperature for growth is 18-25°C, 18-24°C from April to September, and 13-16°C from September to April of the following year. The winter temperature should not be lower than 10°C. It prefers humidity, and poinsettia is relatively sensitive to moisture; during the growing period, it only needs a sufficient supply of water. It prefers sunlight, and during the stem and leaf growing period it needs sufficient sunlight to promote rapid and luxuriant stem and leaf growth.

Propagation Methods for Poinsettia

1. Cuttings: The main cutting propagation methods for poinsettia are semi-hardwood cuttings and softwood cuttings, and there is also old-root cutting. Regardless of which cutting propagation method is used, poinsettia cuttings should preferably be taken in the early morning, because at this time the cuttings have a relatively sufficient moisture content. When cutting the cuttings, the cut should be smooth, and the split epidermis and xylem should be trimmed off to avoid water accumulation and rot, which would affect healing and rooting.

2. Layering: Poinsettia generally uses the air layering propagation method, and the best time for layering is from April to July. Select lignified branches, generally healthy and plump branches from the previous year, and perform ring barking at a smooth part. The width of the ring bark should be similar to the thickness of the branch at the ring-barked area, generally 3-4 cm. After layering, roots usually grow in about two months. At this time, it can be cut off and planted in a pot, forming a new plant.

Cultivation Methods for Poinsettia

1. Soil: Poinsettia prefers loose, well-drained soil. Generally, use 3 parts vegetable garden soil, 3 parts humus soil, 3 parts leaf mold, and 1 part decomposed cake fertilizer, mixed with a small amount of cinder.

2. Temperature: Poinsettia prefers warmth and fears cold. In mid-to-late September each year, move it indoors and increase ventilation so the plant gradually adapts to the indoor environment. In winter, the room temperature should be maintained at 15°C to 20°C. This is exactly the period of bract color change and flower bud differentiation. If the room temperature is below 15°C, flower and leaf development will be poor. After mid-December, it enters the flowering stage, and ventilation should be gradually increased.

3. Light: Poinsettia prefers sufficient light and is strongly phototropic; it is a short-day plant. It should receive sufficient light throughout the four seasons, and this is even more important during bract color change, flower bud differentiation, and flowering. If light is insufficient, branches tend to grow leggy and are prone to disease, and flower color is dull. If placed in a dark place for a long time, it will not bloom and will drop leaves in winter. To make it bloom earlier or later, light can be controlled. Generally, giving 8 to 9 hours of light per day will allow it to bloom in 40 days.

4. Fertilizing: Poinsettia prefers fertile sandy soil. In addition to adding organic fertilizer and horseshoe slices as base fertilizer when potting and repotting, during the growing and flowering season apply a diluted 5-fold fully decomposed sesame paste residue liquid fertilizer once every 10 to 15 days. After autumn begins, a 0.3% compound chemical fertilizer can also be applied once a week for 3 to 4 consecutive times to promote bract color change and flower bud differentiation.

5. Watering: Poinsettia is neither tolerant of drought nor of waterlogging. Watering should be flexibly controlled according to the weather, potting soil, and plant growth conditions. Generally, watering should keep the potting soil moist without accumulating water, but after flowering, watering should be reduced. Watering should be even to prevent excessive dryness or wetness; otherwise, the lower leaves of the plant will turn yellow and fall off, commonly known as "bare legs," or the branches will grow unevenly.

6. Pinching: About 3 weeks after planting, when the root system has grown, poinsettia can be pinched. When pinching, leave 4-6 leaf nodes and raise the temperature to a daytime temperature of 28-30°C and a nighttime temperature of 23°C. Mist frequently to increase humidity, and continue for about two weeks. After buds are seen growing, slowly lower the temperature to 25-28°C during the day, and humidity should also be reduced. During this period, according to the uniformity and fullness of the plant, carry out a second pinching, supplement nutrients, and combine this with treatment using a dwarfing agent.

7. Pruning: Around Qingming Festival, repot the dormant old plant of poinsettia, cut off old roots and diseased or weak branches, and promote the sprouting of new shoots. During the growth process, pinching should be done twice: the first in late June and the second in mid-August. During cultivation, heavy fertilization and heavy watering should be controlled, especially before the plant shape is set in autumn. When the branches grow to 20-30 cm, begin shaping and bending, with the aim of making the plant short and compact, with neat flower heads evenly distributed, improving ornamental value.

8. Plant Height Control: During the cultivation of poinsettia, plant growth regulators must be used to dwarf the plant height so as to meet the requirement of consistent height for commercial flowers. In addition, maintaining consistency between day and night temperatures during cultivation is also crucial and should be tracked and monitored at all times. When the day-night temperature difference exceeds 3°C, after sufficient pinching, spray 750 to 1000 ppm chlormequat 1 to 4 times to inhibit stem legginess.

Pest and Disease Control for Poinsettia

1. Gray Mold

[Symptoms]Gray mold mainly occurs in winter, exactly during the flowering season of poinsettia. Once there is continuous rain, dampness, and no sunlight, it can harm poinsettia flower clusters, bracts, leaves, and branches. Generally, water-soaked lesions first appear on the flower clusters. Afterward, the lesions are covered with a layer of pathogenic fungal conidia, and the pathogen continues to spread to the bracts. In the early stage, the bracts produce water-soaked discolored spots, which then gradually expand into irregular shapes. The pathogen then spreads to the branches, producing yellow-brown to brown lesions on the branches. In the later stage, the lesions clearly sink downward and become dark brown. In severe cases, the lesions become dry and withered.

[Control]Taking advantage of the closed characteristics of the facility, create a high-temperature, low-humidity ecological environment to control the occurrence and development of gray mold. At night, indoor humidity in the facility is often higher than 90%. After raising the mat in the early morning, immediately open the ventilation openings to ventilate and remove moisture, reduce indoor humidity, and control disease development with a relatively low temperature. After 9 o'clock, when the indoor temperature rises faster, close the ventilation openings to quickly raise the indoor temperature to about 32°C.

2. Root Rot

[Symptoms]It generally occurs more severely in high-temperature seasons, and is also very likely to occur when the cultivated soil has a high water content. In the early stage, the plant shows wilting. If the stem base is examined at this time, a light brown constriction can be seen, but the infected plant shows no decay or hydrolysis. Later, the lesions gradually spread upward, and the wilting gradually becomes more severe. The stem lesions are slightly sunken and yellow-brown. In the later stage, the tissue at the lesions disintegrates, causing the plant to wither and die due to severe water shortage. Sometimes the whole plant turns yellow in a water-soaked manner and eventually rots and dies. White mycelium can be seen near the ground, and in severe cases it can spread to the cultivation soil. When the roots are affected, root rot often results, initially affecting the normal growth of the plant and in severe cases leading to death.

[Control]① Practice crop rotation: rotate every other year in lightly diseased fields, and rotate every 3-5 years in heavily diseased fields. ② Deep plowing and soil improvement: increase organic fertilizer, ensure reasonable irrigation and drainage, and enhance disease resistance. ③ Strict seed selection: eliminate unqualified seeds. Treat seeds with 50% carbendazim wettable powder at 0.5% of seed weight. ④ When disease occurs, spray the stem base of peanuts with a 1000-fold solution of 50% carbendazim wettable powder, using 25-30 kg of liquid per mu each time.

3. Leaf Spot

[Symptoms]Leaf spot occurs more severely mainly in spring and summer, and the lesions mostly begin on old leaves. In the early stage, small purple-red to brown spots appear on the leaves. The lesions are nearly circular to irregular, and then gradually expand. Many lesions can merge with each other to form one large lesion. In the later stage, the center of the lesion gradually turns gray-brown. In severe cases, the lesion tissue becomes gangrenous, causing the leaves to twist and dry up.

[Control]① Remove diseased tissue promptly and burn it in a centralized manner. ② Crop rotation (soil can be changed in greenhouses). ③ Do not spray water over the plants. ④ Begin spraying from the early stage of disease occurrence to prevent the disease from spreading and expanding.

4. Whiteflies

[Symptoms]Adults and larvae of whiteflies prefer dense, shaded environments. They gather on the undersides of the upper leaves of poinsettia and suck sap with piercing-sucking mouthparts, causing leaves to fade or develop chlorotic spots, affecting photosynthesis and leading to poor plant growth. The honeydew excreted by the insects often causes sooty mold. Adults are attracted to yellow.

[Control]For whiteflies, the newly mobile young larvae are the most vulnerable, followed by newly emerged adults, which are sensitive to pesticides and suitable for spraying control. Whiteflies generally occur in large numbers under high temperature and low humidity, with the peak period from late September to late November. The optimal control period is late September, and the spraying time is from 6 to 10 a.m.