Japanese honeysuckle (*Lonicera japonica*) is a twining vine native to East Asia. It features white-yellow flowers that emit a pleasant, sweet aroma and are often visited by pollinators such as honeybees, but some parts of the plant are toxic to humans. In landscaping, Japanese honeysuckle is used as a groundcover because its dense, fast-growing nature helps prevent weeds and improve soil health.
I. Appearance and Characteristics
Lonicera japonica, known as Japanese honeysuckle and golden-and-silver honeysuckle, is a species of honeysuckle native to East Asia, including many parts of China. It is often grown as an ornamental plant, but has become an invasive species in a number of countries. Japanese honeysuckle is used in traditional Chinese medicine.
Lonicera japonica is a twining vine able to climb up to 10 m (33 ft) high or more in trees, with opposite, simple oval leaves 3–8 cm (1.2–3.1 in) long and 2–3 cm (0.79–1.18 in) broad. When its stems are young, they are slightly red in color and may be fuzzy. Older stems are brown with peeling bark, and are often hollow on the inside.
The flowers are double-tongued, opening white and fading to yellow, and sweetly vanilla scented. The fruit, which is produced in fall, is a black spherical berry 3–4 mm (0.12–0.16 in) diameter containing a few seeds. While the nectar from the flowers can be safely consumed by humans, all other parts of the plant have the potential to be toxic.
II. How to Grow and Care
Sunlight
Japanese honeysuckle likes sufficient sunlight, so plant them where they can receive long lengths of light exposure time. This way they will thrive, growing denser branches and leaves and blooming in brighter colors. If they are planted in shady areas, the branches and leaves of Japanese honeysuckle will be more sparse and have fewer flowers and fruits. However, note that when the temperature is high and the sunlight is strong in the summer, these plants need shades to prevent too much sun exposure.
Temperature
Japanese honeysuckle grows in temperate and subtropical zones. The plants enjoy warm weather and are suited to grow in an environment with a temperature of 10 to 30 ℃. When the temperature is close to 10 ℃, some of their leaves turn yellow. When the temperature is lower than 5 ℃, almost all of the leaves will wither and fall. When the temperature is higher than 35 ℃, the plant’s speed of growth slows. When Japanese honeysuckle has just been planted, it requires regular watering. However, once established it does not require much water. It is a type of hedge that requires relatively less water.
Watering
Regularly check the moisture of the soil to determine whether a plant needs watering. If the soil is relatively dry, then water it to maintain a slightly moist soil condition. Japanese honeysuckle in gardens with ample rainfall does not need watering. Make sure water does not accumulate in the soil. In drier weather, water the plants appropriately.
During summer, increase the amount of water provided. In winter, reduce it. Wait until the soil turns a lighter color before watering. It is recommended to water japanese honeysuckle once every 3-5 days after pruning leaves or cutting off flowers. This will help it develop new branches and bloom more impressively. It is best to water it in the morning or early evening. Rainwater or snow water is better for watering than tap water. Tap water contains fluoride or chloride, which can cause soil compaction and worsen soil permeability, affecting the breathing of the roots.
Soil
Japanese honeysuckle has strong adaptability and no special soil requirements. The plants can be grown in clay or sandy soil. They like rich, moist, well-drained, and sandy loam the most, and are adaptable to soil with a pH of 6-8, which is slightly acidic, slightly alkalic, or even saline soil.
Fertilizing
When planting japanese honeysuckle in gardens, applying sufficient base fertilizer usually ensures normal growth. If they are planted in flower pots, apply water-soluble organic fertilizer in low concentrations once every 15-20 days in spring and summer. This will allow them to grow more healthily and produce better blooms. When buds appear, mix the organic fertilizer solution with an appropriate amount of fertilizer rich in phosphorus and potassium once or twice. This can promote more blooms and more beautiful flowers.
Planting Instructions
Plant Lonicera japonica either via transplant or by seed. In areas where Japanese honeysuckle is deciduous, transplant shrubs in late winter. Where the shrubs are evergreen, plant in temperate seasons, in spring or fall. Grow new plants from seed in winter, and transplant them out in spring. Choose an area for your transplants in full sun that has average, well-draining soil. Dryer areas and those with partial shade keep the aggressive vine in check. Choose a place around small trees or use the plants as ground cover for erosion control. They’re excellent in containers, too.
To transplant this trumpet creeper, prune it to ⅓ its size and dig a hole large enough to fit the roots and soil from its nursery pot. Place the root system in the hole and cover it with soil. Mound the base of the plant slightly for good drainage. Provide adequate support for the vine and vegetation.
To sow Japanese honeysuckle seeds in spring, soak peat moss in water and wring it out. Then bundle the peat and press the seeds into it, placing the whole mass in a clear plastic bag. Seal it and put it in the refrigerator for 60 days. Then sow them in flats with peat moss and potting soil. Wrap the flats with plastic wrap or cover them with a dome. Within 30 days seed germination occurs.
Pruning
Pruning should usually be done in fall after the leaves of japanese honeysuckle drop, before germination. Fertilizing and pruning after blooming can encourage Japanese honeysuckle to bloom again. Stronger branches need light pruning while weaker branches need hard pruning. Dry or old branches need to be completely pruned because pruning older branches can help younger branches develop. Pruning the branches in the middle can promote air circulation in the center of the plant while also letting lower branches receive more sunlight.
After pruning, the plant’s branches will bloom at similar times, so you can harvest more flowering branches at a time. It is recommended to just lightly prune newly planted japanese honeysuckle as long as its shape is controlled.
Propagation
The main propagation method of Japanese honeysuckle is cutting. This can be done in all seasons except for winter. Select solid branches that have sprouted for 1-2 years and are approximately 35 cm long. Remove the lower leaves and apply rooting powder to the cuts, then stick them in perlite or vermiculite. Before they take root, be sure to promptly provide shade and water to prevent the branches from drying out. If cutting is propagated during the rainy season, a branch can root after half a month.
Japanese honeysuckle can also be propagated by layering. Stem nodes buried in moist soil are able to take root. After rooting, the branches can be cut off for transplanting and bloom as early as the next year.
Transplanting
The ideal season for transplanting japanese honeysuckle is from late spring to mid-summer, as this ensures optimal growth. Choose a location with moist, well-draining soil and partial to full sun exposure. Prioritize spacing for better air circulation, and water thoroughly after transplanting.
Pests and Diseases
- Common Pests
While small infestations are the worst you’ll see on the vines, there are a few pests to look out for.
Aphids feed on the sap of leaves and vines and can cause defoliation in extreme cases. To prevent them, start with a strong stream of water from a hose to rip their suckers off their bodies and prevent further feeding. Horticultural oil sprays, neem oil, or insecticidal soap are good follow-up measures if necessary. Do not spray the vines when they flower. Instead, wait until after that time, and apply sprays in intervals of 7 to 10 days until the aphids are gone.
European honeysuckle leafroller moths lay eggs on the leaves of the vine. The eggs hatch and small striped caterpillars feed on the leaves. Eventually, they roll their cocoon up in a leaf, and the cycle continues. Remove cocoons as you find them, and spray horticultural oil or spinosad spray on leaves to prevent leafrollers.
Honeysuckle sawflies curl up the undersides of leaves as they feed on the vine. These small striped insects with cloudy wings lay eggs that produce 1 inch long larvae that keep the feeding going. We recommend the use of spinosad to prevent sawflies from feeding on the vegetation.
- Common Diseases
Leaf blight is a fungal disease that causes gray spots, and thickened curled leaves. In later stages, the spots develop spores that spread by wind to other parts of the trumpet creeper. Prune and destroy affected branches, and apply copper fungicide sprays in spring when new growth emerges to prevent leaf blight.
Powdery mildew is a fungal disease that produces white patches on leaves. While it’s not a serious problem, it’s highly contagious. Remove any diseased leaves as they appear. Copper fungicides also treat the issue. Spray them as soon as symptoms appear, and reapply in intervals of 7 to 10 days until the problem ceases.
Crown gall is a bacterial disease that causes swelling and rough galls at the base of the trailing vine. Prune effectively with clean cuts to prevent bacterial entry at wounds. Keep your pruners and garden tools clean and disease-free as another prevention method. Overall, affected honeysuckles should be removed and destroyed to prevent spreading the bacterial infection to other plants in the garden.
- Common Problems
In too much shade, flowers may not be as prolific on your honeysuckle. If fragrant blooms are what you seek, try to find a happy medium between shade and full sun. Prune overhead branches to adjust and add more sunlight. Shade the plant if it produces too much. In heavy clay soils, honeysuckle can suffer from nutrient deficiencies which could cause yellow leaves. Provide adequate drainage from the get-go, or introduce drainage elements in a ring around the vines to adjust.
III. Uses and Benefits
- Ornamental uses
Japanese honeysuckle (Lonicera japonica) has a lot to offer as an ornamental plant since this climbing vine produces long-blooming fragrant and showy flowers from late spring to fall. It is primarily used as an attractive groundcover or to decorate walls, fences, and trellises in coastal, cottage, and informal gardens. However, japanese honeysuckle is best grown alone or in small numbers when carefully controlled. The white flowers work well when combined with the brightness of roses.
- Medicinal uses
Herbal medicine
In traditional Chinese medicine, Lonicera japonica is called rěn dōng téng (忍冬藤); literally “winter enduring vine”) or jīn yín huā (Chinese: 金銀花; literally “gold-silver flower”, in reference to the presence of flowers of different age on the same plant as each flower change from white (silver) to yellow (gold)). Alternative Chinese names include er hua (二花) and shuang hua (雙花), meaning double-[color] flowers.
The dried leaves and flowers (Flos Lonicerae Japonicae) are employed in traditional Chinese medicine, where they are believed to be of use to treat fever, cold-related headache, cough, thirst, certain inflammation including sore throat, skin infection, and tumor necrosis.
Antiviral action
The antiviral action of loniflavone, a compound found in Lonicera japonica, has been investigated in computational studies, in which the ability of this compound to bind with high affinity to the spike protein of SARS-CoV-2 has been demonstrated, an early step towards drug development for the disease caused by that virus.
