Rose of Sharon (Hibiscus syriacus 'Diana')

Overview

Hibiscus syriacus ‘Diana’ is a favored cultivar of the Rose of Sharon, cherished for its reliable and extended bloom period lasting from mid-summer well into autumn. This vigorous, upright deciduous shrub produces showy, hollyhock-like flowers of pure white, contrasting beautifully against its attractive green foliage. Gardeners appreciate the Hibiscus syriacus ‘Diana’ for its low maintenance requirements and exceptional tolerance to heat, humidity, and challenging soil conditions, making it a dependable backbone plant in many landscapes.

As a multi-stemmed shrub, it easily transitions into a small tree form if desired, offering vertical interest. The ‘Diana’ cultivar is particularly noted for being triploid, meaning it produces very few viable seed pods, reducing potential self-seeding issues common in the species. Planting the Rose of Sharon ensures continuous late-season color when many other shrubs have finished flowering.

Its adaptability makes the Hibiscus syriacus ‘Diana’ an excellent choice for screening, borders, or as a specimen plant where its clean white flowers can truly shine. When properly sited, this versatile shrub requires minimal supplemental care throughout the growing season.

Fast Facts

• Plant Family: Malvaceae
• Plant Type: Deciduous shrub
• Hardiness Zones: USDA Zones 5-8
• Size at Maturity:
  • Height: 5-8 ft
  • Spread: 4-6 ft
• Bloom Time: July to October
• Bloom Description: Pure white with no eye
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Low

How to Grow

Planting should ideally occur in spring or early fall to allow the Rose of Sharon roots time to establish before extreme heat or cold hits. Choose a location providing full sun for the best flowering display, although Hibiscus syriacus ‘Diana’ tolerates part shade. It thrives in average, medium moisture, well-drained soils but is notably tolerant of poorer soils, clay, and provides drought resistance once established.

Water moderately during the first growing season; thereafter, this shrub handles periods of drought well, though consistent moisture promotes healthier growth. Fertilizing is usually unnecessary unless soil quality is extremely poor. Pruning is best performed in spring when buds are just beginning to swell. Pruning back the branches to just 2-3 buds can encourage significantly larger blooms on the Hibiscus syriacus ‘Diana’.

This shrub shows excellent tolerance to summer heat and humidity, making it reliable in warmer climates. While generally robust, be aware that it is generally tolerant of urban pollution. Stem cuttings offer an easy method for propagation, although seeds will not reliably produce the desirable pure white flowers of the parent plant.

Landscape Uses

The Rose of Sharon excels in various formal and informal landscape settings due to its vase shape and extended flowering period. It is highly recommended when massed together for a dramatic screen or used as a structural element in shrub borders. The uniform growth habit makes Hibiscus syriacus ‘Diana’ a fantastic choice for hedges that offer both seasonal screening and summer flowers.

For foundation plantings, use smaller specimens unless you desire a taller, more informal look. Avoid overcrowding, allowing air circulation which helps minimize potential foliage diseases. To create a classic garden look, pair the white blooms of the Rose of Sharon with blue or purple flowers like Russian Sage or Catmint for high-contrast summer beds.

When utilizing the plant as a hedge, ensure consistent spacing appropriate for its mature spread of 4 to 6 feet. Its upright nature also allows it to be trained vertically as a small specimen tree or espalier against a sun-drenched wall.

Standout Features

Flower Qualities

• Showy

Noteworthy Characteristics

Hibiscus syriacus, commonly called rose of Sharon or shrub althea, is a vigorous, upright, vase-shaped, multi-stemmed, deciduous shrub that typically grows 8-12’ tall. It may be trained as a small tree or espalier. Showy, hollyhock-like, 5-petaled flowers (to 3” diameter) appear over a long, early-summer to fall bloom period. The cultivar ‘Diana’ features pure white flowers that are 3 to 4 inches across and holds the distinction of being a Royal Horticultural Society of Great Britain Award of Garden Merit plant.

Tolerances

• Deer
• Drought
• Clay Soil
• Black Walnut

Potential Problems

The Rose of Sharon can occasionally display susceptibility to common fungal issues, including leaf spots, blights, and rusts, as well as canker. Good air circulation, achieved through proper spacing and pruning, is the best preventative measure against these diseases. Monitor plants regularly, especially during wet springs, and treat promptly with appropriate fungicides if spots appear.

Insect pests are sporadic visitors, with aphids, whiteflies, and most notably, Japanese beetles being occasional problems. Japanese beetles are particularly destructive as they can rapidly skeletonize the foliage if left unchecked. If beetle infestations occur, manual removal or targeted insecticide application during peak activity periods will protect the leaves and ensure the Hibiscus syriacus ‘Diana’ maintains its photosynthetic capacity for optimal flowering.

Frequently Asked Questions

What hardiness zones is Rose of Sharon suitable for?

The Hibiscus syriacus ‘Diana’ is reliably hardy in USDA Zones 5 through 8. Always ensure your planting zone matches this range for optimal long-term health.

How large does Rose of Sharon grow?

This deciduous shrub typically matures to a height between 5 and 8 feet, with a spread ranging from 4 to 6 feet wide. Pruning in early spring can help manage its size.

When does Rose of Sharon bloom?

The bloom time for the Hibiscus syriacus ‘Diana’ is generous, running from July all the way through October, offering pure white, eye-less flowers throughout the late summer and fall.

What sun exposure does Rose of Sharon need?

For best results, plant the beautiful white-flowering Rose of Sharon in full sun, though it will tolerate conditions reaching into partial shade.

Conclusion

The Hibiscus syriacus ‘Diana’ stands out as a low-maintenance, heat-tolerant shrub that guarantees a late-season floral show with its stunning, large, pure white blooms. Providing reliable performance across USDA Zones 5 to 8, this cultivar of the Rose of Sharon avoids aggressive seeding, simplifying garden maintenance. Before planting, confirm that your site offers full sun to part shade conditions and plan your prune for early spring to encourage the best display this season.

Companion Planting

When selecting companions for the Hibiscus syriacus ‘Diana’, focus on plants that share similar full sun and medium water needs, and complement its upright habit. Consider pairing it with low-growing, silver-leafed plants like Lamb’s Ears (Stachys byzantina) at the base to provide textural contrast and suppress weeds around the root zone. For color contrast that lasts into autumn, plant perennials such as ornamental grasses like Karl Foerster Feather Reed Grass, whose fine texture balances the broad leaves of the Rose of Sharon. Alternatively, blue or deep purple perennials, such as Salvia or Russian Sage, create dynamic complimentary color schemes against the white flowers of the Hibiscus.

Propagation Tips

While the species form of Rose of Sharon can readily self-seed, the superior triploid ‘Diana’ cultivar is best multiplied vegetatively to ensure true-to-type flowering. Softwood cuttings taken from new growth during the early summer months offer the greatest success rate. Take cuttings just below a leaf node, remove the lower leaves, and dip the base in rooting hormone before planting in a sterile, moist medium, ideally placed under humidity-controlled conditions or a mist bench. Hardwood cuttings taken in late fall while the plant is dormant are another viable, though sometimes slower, method for increasing stock of the Hibiscus syriacus ‘Diana’.