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Hypericum kalmianum Cobalt-n-Gold - St. John's wort

Hypericum kalmianum Cobalt-n-Gold®
Kalm's St. John's Wort, Kalm St. Johnswort

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A very decorative variety of Kalmian St. John's Wort. Its deciduous bluish foliage is made up of narrow leaves that turn orange in autumn before falling. It displays a bright yellow flowering in summer, well enhanced by the green-blue foliage. Its spreading habit, wider than tall, makes it an ideal plant for slopes. This bush is very adaptable, thriving in full sun or partial shade, in neutral to limestone soil, moist to dry, even poor. Hardy and enduring, it is an excellent choice for beginners in gardening.
Flower size
4 cm
Height at maturity
1 m
Spread at maturity
1.50 m
Exposure
Sun, Partial shade, Shade
Hardiness
Hardy down to -29°C
Soil moisture
Dry soil, Moist soil
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Best planting time March, October
Recommended planting time February to April, September to November
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Flowering time June to July
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Description

If their massive use a few years ago may have tired of Millepertuis, the Hypericum kalmianum 'Cobalt-n-Gold' heralds the revival of the genus with an attractive bush in more ways than one. Compact, it forms a spread out bush of a bluish colour that is very impressive. Its narrow and fine leaves are decorative throughout the season, and even more so in autumn, when they turn orange before falling. The classic yellow flowers bloom in summer and are particularly enhanced by the green-blue mass of foliage. Winter allows you to enjoy the decorative bark, which is cinnamon in colour. Hardy, tolerating most growing conditions, it is the ideal plant to start in the garden, perfect for filling a slope or in association in a mixed border. 

The Hypericum 'Cobalt-n-Gold' is a recent horticultural creation (2008) derived from Hypericum kalmianum, a botanical species native to North America. This small bush belongs to the Hypericaceae family (or Clusiaceae according to classifications, and formerly Guttiferae). Of medium growth, it generally does not exceed 100 cm (39.4 in) in height and 1.50 m (4 ft 11 in) in width, depending on growing conditions. It has a dense, rounded, spread out, slightly irregular habit, carried by arched quadrangular stems. They are adorned with long, entire and narrow leaves, often semi-evergreen (depending on the severity of the winter). These elongated, pointed leaves, 4 to 6 cm (1.6 to 2.4 in) long, are a beautiful bluish green and turn yellow to orange-red in autumn. In June-July, it produces abundant clusters of 3-4 cm (1.2-1.6 in) diameter flowers, composed of 5 rounded petals arranged in an open cup. The center of the flower is occupied by a bouquet of prominent stamens, particularly decorative. Hardy to at least -20°C, in cold climates, the dropping of the leaves reveals a beautiful cinnamon-colored bark, which peels off and adds attraction to this shrub.
This Millepertuis is easy to grow, it thrives in neutral to alkaline, moist to dry, even poor soil. Tolerant of soil type, it is also tolerant of exposure, from sunny in cool climates, to partial shade, or even shade in hot climates. 

Millepertuis are appreciated for their long flowering period and their ease of cultivation in all types of soil and in all our climates, even by the sea. As long as you like yellow flowers, Hypericum 'Cobalt-n-Gold' is one of the small shrubs to be planted in a brand-new garden, even for beginners in gardening. It excels in all areas of the garden, whether sunny or shaded and impoverished by tree roots. It only requires well-drained soil to thrive in borders.
In light woodland, for example, it can be associated with symphorines and the male dogwood 'Jolico' to create a wild scene. In sunnier areas, it will accompany the Lavatera 'Burgundy Wine', the Berberis thunbergii Atropurpurea Nana, blue perennial geraniums or an upright conifer with golden foliage like the Taxus baccata David.

Hypericum kalmianum Cobalt-n-Gold - St. John's wort in pictures

Hypericum kalmianum Cobalt-n-Gold - St. John's wort (Flowering) Flowering
Hypericum kalmianum Cobalt-n-Gold - St. John's wort (Foliage) Foliage

Plant habit

Height at maturity 1 m
Spread at maturity 1.50 m
Habit Irregular, bushy
Growth rate normal

Flowering

Flower colour yellow
Flowering time June to July
Inflorescence Cyme
Flower size 4 cm
Bee-friendly Attracts pollinators

Foliage

Foliage persistence Semi-evergreen
Foliage colour green

Botanical data

Genus

Hypericum

Species

kalmianum

Cultivar

Cobalt-n-Gold®

Family

Hypericaceae

Other common names

Kalm's St. John's Wort, Kalm St. Johnswort

Origin

Cultivar or hybrid

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Planting and care

Plant Hypericum Cobalt-n-Gold in a sunny position, or in partial shade to shade in a warm climate, sheltered from dry and cold winds. Its foliage can be damaged by too much sun. This St. John's wort appreciates well-drained soils and dreads excessive humidity in winter. In heavy soils, it is useful to mix a good amount of coarse sand or gravel with the garden soil to improve drainage. It adapts very well to sandy or limestone and poor soils, moist to dry in summer. It is very tolerant, but it prefers slightly alkaline soils. It needs a fairly deep soil to allow it to find some freshness that will help it escape drought in hot regions. It is hardy to at least -20°C (-4 °F), not very susceptible to diseases, and its enemies are rare. Pruning is not necessary for this well-branched variety. However, if it is necessary, it will be done sparingly after flowering.

Planting period

Best planting time March, October
Recommended planting time February to April, September to November

Intended location

Suitable for Meadow, Woodland edge
Type of use Border, Hedge
Hardiness Hardy down to -29°C (USDA zone 5) Show map
Ease of cultivation Beginner
Planting density 3 per m2
Exposure Sun, Partial shade, Shade
Soil pH Any
Soil type Chalky (poor, alkaline and well-drained), Silty-loamy (rich and light)
Soil moisture Dry soil, Moist soil, well-drained

Care

Pruning No pruning necessary
Soil moisture Dry soil, Moist soil
Disease resistance Very good
Overwinter Can be left in the ground

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