Other names for purpledisk sunflower (Helianthus atrorubens) include Appalachian sunflower, wild sunflower, and dark-eyed sunflower. It’s a species that’s indigenous to the southeastern part of the United States. It is in fact a member of the sunflower family. However, unlike other species in this family, it prefers to grow by itself instead of with others.
I. Appearance and Characteristics
Helianthus atrorubens is a North American species of sunflower known by the common name purpledisc sunflower. It is native to the southeastern United States. It is found in all the coastal states from Louisiana to Virginia, plus the inland states of Kentucky and Tennessee.
Helianthus atrorubens is a perennial herb sometimes as much as 200 cm (80 inches) tall. Most of the leaves are close to the base of the stem. One plant can produce 1-15 flower heads, each with 10-15 yellow ray florets surrounding 75 or more red or purple disc florets. The plant grows in mixed woods and along roadsides.
II. How to Grow and Care
Purpledisk sunflower is recognized for its resilience and ease of care, thriving in a range of garden environments. Key care points include ensuring full sunlight exposure for optimal growth and consistent moisture, particularly during the blooming period. A special care point for purpledisk sunflower is that it requires well-draining soil to prevent root rot and other moisture-related diseases.
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 native in North America, where it is cold in winter and hot in summer, have a significant annual variation in temperature. Sunflowers likes a warm environment. The suitable temperature for growth is 18 to 30 ℃ and they can grow normally as long as the temperature is not lower than 10 ℃. Within the suitable temperature range, the higher the temperature is, the faster the Sunflowers grow.
In different stages of growth, Sunflowers require different amounts of water, and in general, they are drought-resistant. The soil shall not be too moist and no water logging is important. From the budding period to the flowering period, stable water supply shall be ensured for good blooming.
Watering
Native to North American prairies, purpledisk sunflower thrives in environments that mimic its natural habitat, with moderate moisture and well-draining soil. This species exhibits a balance between drought resistance and a preference for consistent hydration. It should be watered every week to maintain optimal health. Purpledisk sunflower is typically grown outdoors where it can benefit from the seasonal rainfall patterns, aligning with its growth cycles and ensuring adequate water availability during critical developmental stages.
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
For optimal growth, purpledisk sunflower benefits from fertilization with balanced nutrition fertilizers during active growing seasons, spring and summer, and high phosphorus formulas pre-flowering to encourage blooms. Apply every 4-6 weeks, adhering to manufacturer’s guidelines for dosage, to enhance health and vigor. Avoid over-fertilization to prevent root burn. Seasonal adjustments reflect growth; less is required in fall/winter. Water soil before and after applying to distribute nutrients and safeguard roots.
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
Purpledisk sunflower, with its striking flowers, is commonly propagated through sowing. To achieve success, ensure the use of well-draining soil and maintain consistent moisture without waterlogging. Plant the seeds at a shallow depth to allow for sufficient light exposure, which is crucial for germination. For optimal growth, use a fertile substrate and provide ample sunlight. Gentle care during the early growth stages will result in strong, healthy specimens.
Transplanting
For purpledisk sunflower, the prime window for transplanting spans from the awakening of early spring to the genial days of late spring. Choose a sunny spot with well-draining soil. Purpledisk sunflower thrives with ample space for growth—ensure friendly advice by spacing them well.
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.
