Hypericum ascyron: complete guide

Overview

Hypericum ascyron, also known as Great St. Johnswort or Great St. John's-Wort, is a remarkable herbaceous plant from the Hypericaceae family. This temperate-distributed plant is found across Asia from Tibet to Japan and in North America from Canada to North Carolina.

Great St. Johnswort is a robust, upright plant renowned for its large yellow flowers and strikingly thick, square stems. It is an excellent choice for borders and garden areas where a long flowering period and easy cultivation are desired.

Appearance and Bloom

Hypericum ascyron grows as a robust, upright plant with thick, four-angled green stems that can reach up to 1.2 meters in height. The stems feature distinctive winged-like ribs and are highly structural and architectural.

The leaves are opposite, elliptic to lanceolate, approximately 5-10 centimeters long, with fresh green coloring and notably fine veining. The leaves are semi-transparent and allow light to pass through against bright light.

The flowers are the highlight of this plant. They are large, approximately 5-7 centimeters in diameter, brilliant yellow with numerous stamens forming a prominent yellow column in the center. The flowers appear from July through September in rich branched clusters. They are highly attractive to bees and other pollinators.

Ideal Location

Hypericum ascyron grows best in full sun to partial shade. The plant thrives in sunny positions with at least 5-6 hours of direct sunlight daily. In hotter climates, some afternoon shade can be beneficial.

The plant is very winter-hardy and can tolerate temperatures down to -25 to -30 degrees Celsius. This makes it excellent for UK gardens and Northern European climates.

The location should be well-protected from very strong winds, although the robust stems can withstand considerable wind stress.

Soil

Hypericum ascyron grows best in well-draining soil with moderate nutrient content. The plant is fairly undemanding and grows even in poorer soils. An acidic to neutral pH of approximately 5.5 to 7.0 is ideal.

The plant dislikes overly wet soils; waterlogging must be avoided. Well-prepared garden soil, possibly with some additional organic matter, is sufficient.

Once established, the plant is drought-tolerant and does not require much fertilization.

Watering

Hypericum ascyron is relatively drought-tolerant once well-established. Water regularly during the first season until roots are well-established. Subsequently, it only needs extra water during prolonged dry periods.

In containers or very poor soils, more frequent watering may be necessary. Water preferably in early morning or evening to prevent evaporation.

The plant can tolerate brief dry periods without noticeable damage.

Pruning

Pruning is straightforward for Hypericum ascyron. In spring, before new growth begins, prune the plant back to approximately 30 centimeters in height. This encourages a compact, upright form.

Thereafter, it can be lightly pruned back to encourage branching. Faded flowers can be removed, although this is not essential.

After very cold weather, dead material may need to be removed.

Maintenance Calendar

March-April: Heavy spring pruning. Add fertilizer. Begin watering. May-June: New growth. Regular watering. No additional feeding needed. July-September: Flowering period. Deadheading possible. Minimal care. October-November: Flowering begins to decline. Gradually reduce watering. December-February: Plant rests. Remove dead material. Frost protection usually unnecessary.

Winter Hardiness

Hypericum ascyron is very winter-hardy. The plant can tolerate temperatures down to -25 to -30 degrees Celsius without damage. This is excellent for UK winters and Northern European climates.

The plant may die back in very severe winters but usually regrows from the roots in spring.

Companion Plants

Hypericum ascyron combines well with:

• Salvia: purple flowering plant
• Coreopsis: yellow flowering plant for continuity
• Rudbeckia: larger yellow flowers
• Stipa: grass for movement and texture
• Achillea: pink or yellow flowering plant

Together they form an attractive summer flower composition.

Conclusion

Hypericum ascyron is an exceptionally beautiful plant for those seeking long flowering periods and striking structure. With its enormous yellow flowers and thick square stems, it adds dramatic visual interest to any border.

The plant is very winter-hardy, drought-tolerant, and requires minimal maintenance. For those interested in easy-to-grow summer bloomers with characteristic appearance, this is certainly worth trying.

Available from plant nurseries and garden centers. Try this fascinating plant and enjoy its extended flowering season.