Silverleaf spurflower is renowned as one of the most beautiful plant species to hail from South Africa, where it grows prominently on forest floors. Due to the contrast created by its bright white flowers against the dark shade of its leaves, this plant is sometimes said to resemble the look of lit candles.
I. Appearance and Characteristics
Plectranthus oertendahlii is a species of flowering plant in the sage and mint family, Lamiaceae. Common names include silverleaf spurflower, Swedish ivy, Oertendahl’s spurflower, November lights and Brazilian coleus, though it is native to eastern South Africa rather than Brazil. Plectranthus oertendahlii and the cultivar ‘Uvongo’ have gained the Royal Horticultural Society’s Award of Garden Merit.
Growing to 20 cm (7.9 in) tall, it is a tender forest-dwelling perennial, with somewhat succulent heart-shaped leaves whose surface is strikingly marked with silver, while the undersides are a deep reddish purple. The undersides contain the chemical anthocyanin, which helps to trap what little light is available beneath the forest canopy. The stems are square, creeping and rooted. The leaves are slightly succulent, rounded to rhombic and roughly serrated. The top of the leaves is dark green with silver veins in silver, and the underside is deep red.
The pink-tinged white or pale blue flowers, held in erect sprays above the foliage, are double-lipped and resemble those of its relatives in the genus Salvia (sage). It blooms in autumn and winter.
P. oertendahlii is named for Ivan Anders Oertendahl of Sweden’s Uppsala University. Nobody knows how the plant reached Sweden, but it has been cultivated in Scandinavia for over a century, and remains popular there. It increases both by setting seed and by putting down roots as it spreads along the ground.
This plant and its cultivars are widely grown as ornamentals, often under its former name Coleus. In temperate climates it is grown as a houseplant, as it does not tolerate temperatures below 5 °C (41 °F). However, plants may be placed outside in a warm shaded area during the summer months.
II. How to Grow and Care
Silverleaf sunflower is a low-maintenance plant ideal for gardeners seeking minimal care requirements. It thrives in full sunlight and well-draining soil, making it suitable for xeric gardens. Special care points include ensuring proper spacing to prevent overcrowding and support for its tall stems to resist wind damage. Regular deadheading promotes continued blooming throughout the growing season.
Sunlight
The seedlings, leaves, and flower heads of sunflowers all exhibit very strong phototropism. Sufficient sunlight will make the seedlings grow strongly and healthily. During the middle period of their growth stage, sufficient sunlight can promote the growth of stems and leaves and the differentiation of flower buds. If sunflowers receive sufficient sunlight during their entire growth period, the stems and leaves grow healthily and the flowers are vivid and bright. However, if there is continuous rain or they are grown for a long time in a partially shady spot they may grow poorly and become weak. The stems will not be straight, the leaves will be soft and droop in yellow green, and the flower head will be small and irregular.
Temperature
Sunflowers were originally native to North America, where it is cold in the winter and hot in the summer, meaning there is a significant annual variation in temperature. Sunflowers like a warm environment. The most suitable temperature for their growth is 18 to 30 ℃, and they can happily grow as long as the temperature is not lower than 10 ℃. Within this suitable temperature range, the higher the temperature is, the faster sunflowers grow.
At different stages of their growth, sunflowers require different amounts of water, although in general they are drought-resistant. However, their soil should not be too moist since waterlogging soil can kill them. During the budding and flowering period, sunflowers should be regularly watered, to ensure better blooming.
Watering
Silverleaf sunflower hails from regions with a relatively balanced water distribution. It has developed a preference for moderate humidity, showing neither drought tolerance nor an inclination towards excess moisture. Watering silverleaf sunflower once every 1-2 weeks will cater to its needs efficiently. Typically thriving outdoors, this deciduous plant’s growth cycle is highly influenced by the availability of water, making it crucial to maintain its watering schedule.
Soil
Sunflowers can grow well in all types of soil. However, the soil they most prefer is sandy loam or loamy soil, with a pH of between 5.8 and 6.5. Good soil drainage is crucial for the growth of sunflowers. If sunflowers are planted in the garden, it is recommended that loose and fertile loam is used, which can be mixed with decomposed compost as a base fertilizer. Quick-acting fertilizer can also be added. Soil should be dug over prior to fertilization and sowing to improve soil structure and drainage.
If sunflowers are grown in pots, their soil should be made up of peat, vermiculite, and sand in the ratio 2: 1: 1; organic fertilizers can be mixed in at the same time. Please note that sunflowers should not be continuously planted in the same soil or in soil where other plants of the same family have been planted, otherwise they will grow poorly. It is recommended that the soil is replaced once a year, or that sunflowers are grown in a different area.
Fertilizing
When sunflowers are grown in pots, liquid fertilizer or compound fertilizer should be applied once every 7 to 10 days. During the growth of seedlings, nitrogen fertilizer should be applied to promote the luxuriant growth of stems and leaves. When budding begins, more phosphate-potassium fertilizer should be applied, which will provide sufficient nutrients to promote robust growth of the buds and facilitate blooming.
If sunflowers are planted in the garden, no fertilizer is required if the soil is already fertile. However, if the soil is relatively poor, nitrogen fertilizer should be applied during the early stages of growth and phosphorus and potassium fertilizers should be applied during the late stages, similar to that carried out for potted plants. They can be fertilized once every 20 days during the growth period, with an additional two or three applications of thin phosphate-potassium fertilizer provided before blooming.
Planting Instructions
Sunflowers are generally sown in late winter or spring and will bloom 60 to 70 days after sowing. The seeds should be sown directly into the soil, with spacing between the seeds of at least 12 cm. After sowing, a 2 cm layer of fine soil should be used to cover the seeds. Then, the seeds should be watered before being covered with a layer of mulch.
If sunflowers are sown in seed trays, deep seed trays should be used. First, place the compost into the seed tray, thoroughly water it, and wait for the excess water to drain before sowing. Sow each seed in a hole, cover it with a thin layer of soil, place the tray in a shady place, and wait for the young seedlings to appear.
Once the seedlings appear, ventilate them well, reduce the humidity and temperature, and gradually expose the seedlings to sunlight. Two weeks after sowing, the seedlings will grow to about 5 cm. At this time, the seedlings can be transplanted into a 10 cm pot and cared for until planting out. The optimum soil temperature for planting sunflowers is 15 ℃.
Pruning
To ensure the robust growth of the main stem, the lateral buds of sunflowers should be removed so as not to distribute nutrients too widely and affect the growth of flowers on the main stem. If planted in a border, the top bud of the main stem can be picked off, so that branching occurs to give 4-5 blooms and the plant remains quite short and bushy.
For sunflowers planted to provide cut flowers, the apical bud should be removed to facilitate the growth of lateral stems. After such treatment, several stems will be produced, and 7-10 flowers can be harvested from one plant. For sunflowers grown in pots, it is recommended to keep the primary stem and remove the lateral buds, since in this case it is better to have just one flower.
Propagation
Sunflowers are usually propagated by sowing seeds. It is a cross-pollinated plant that can be naturally pollinated by insects and bees, although artificial pollination can also be carried out when sunflowers are in bloom, which can improve the seed setting rate and produce more seeds.
Transplanting
For silverleaf sunflower, the quintessential time to transplant is from the awakening of spring until the cusp of summer, capturing robust growth. Choose sunny spots with well-draining soil, and consider enriching the bed before transplantation for best establishment.
III. Harvesting and Storage
For sunflowers planted to be used for cut flowers, they can be harvested when the outermost ligulate flowers bloom. It is best to harvest them in the early morning when the temperature is low; they should not be harvested at midday or in the afternoon, when the temperature is high. Gardening scissors should be used to cut the inflorescences obliquely at the bottom of the stem; this can increase the area for water absorption.
The cut inflorescences should be placed in a container of clean water as soon as possible to avoid water loss. If the flower cannot be placed into water immediately, the bottom of the stem should be cut again before it is placed in water to ensure sufficient water absorption. The vase life of sunflowers is 6 to 8 days in the summer and 10 to 15 days in the winter.
