The Brunnera macrophylla ‘Jack Frost’, often called Siberian Bugloss, is a highly sought-after perennial for shade gardens. It is prized for its distinctive foliage: heart-shaped leaves covered in a striking silver overlay, leaving only the veins and edges green. Airy sprays of tiny, pale blue flowers, resembling forget-me-nots, appear in mid-spring. Many gardeners wonder if this popular groundcover possesses an aggressive spreading habit.
Understanding the Clumping Growth Habit
The core characteristic of ‘Jack Frost’ is its strictly clumping growth habit; it is not a fast or aggressive spreader. Unlike groundcovers that rapidly colonize an area, this perennial expands very slowly outward to form a dense, tidy mound. This controlled spread is achieved through short, creeping rhizomes, which are underground stems that allow the plant to spread vegetatively. Because ‘Jack Frost’ produces these rhizomes slowly, the clump size increases gradually over many years while maintaining a compact, mounded form. This slow expansion and lack of long runners means the plant is easily managed and contained, making it effective as a specimen or controlled ground cover in shaded borders.
How New Plants Emerge: Seeding and Division
New Brunnera plants can emerge through self-seeding or physical division. While the species Brunnera macrophylla self-seeds readily, ‘Jack Frost’ is a genetically distinct cultivar. If the flowers produce viable seeds, the resulting seedlings will not retain the desirable silver variegation. The genetic trait for the frosted foliage is unstable when reproduced sexually, causing seedlings to revert to the plain green coloration of the parent species. To ensure the new plant has the striking silver pattern, propagation must be done asexually, primarily by dividing the mature clump, which guarantees genetically identical clones.
Controlling Size and Ideal Placement
Since ‘Jack Frost’ is a clumping plant, division is rarely needed for containment. However, gardeners can divide the perennial every three to four years to maintain vigor or create new plants. Division is best performed in early spring before new growth or in early fall. Promptly removing spent flower stalks helps prevent unwanted self-seeding and the appearance of plain green seedlings. The plant thrives best in partial to full shade, as intense afternoon sun can scorch the delicate foliage; ideal placement requires consistently moist, organically rich, and well-drained soil.