Hypericum kalmianum Kalm's St. John's Wort Description Blooms golden-yellow flowers. Green foliage.Bloom Period: Late Spring into SummerGrowth Habit: Dwarf and rounded Mature Height: 2' to 2.5' (60 cm to 75 cm)Mature Spread: 2' to 2.5' (60 cm to 75 cm)Growth Rate: Slow More Details Sun Exposure: Full sun to partial shadeCold Hardiness Zone: 4Drought tolerantLong bloomingAttracts butterfliesLandscape Uses: Foundation planting, container and gardenNative to Ontario