How tall does brunnera get is a fair question to ask before you plant. The plant reaches 12 to 18 inches (30 to 45 centimeters) tall at full size per NC State Extension data. The leaf mound stays a bit shorter than the flower stems in spring. You can plan your bed with full trust in these size limits for years to come.
Brunnera height has two parts you should know about for good planning. The leaf mound alone reaches just 10 to 12 inches tall in most years. The flower stems push up to 18 inches tall in spring for the bloom show. Once the flowers fade, the plant goes back to the shorter leaf mound for the rest of the season.
I have a row of Jack Frost brunnera in my front bed that I have measured for years. The clumps hit 18 inches tall at peak bloom in early May each year. By June, the flower stems are gone and the leaf mound sits at about 12 inches tall. The plants stay at this height for the rest of the summer and fall.
Brunnera mature size also includes the spread of the clump, not just the height. Most plants reach 18 to 30 inches (45 to 75 centimeters) wide at full size. The width grows a few inches each year as the rhizomes push out. Some big-leaf forms like Looking Glass spread a bit wider than the basic types.
I have found that mature size takes about three years to reach from a one gallon pot. Smaller four inch pots may need a full year longer to catch up. Plant your brunnera with full size in mind from day one. This saves you from moving plants later when they fill in their space.
Light also plays a role in how tall your brunnera will grow each year. Plants in deep shade tend to grow a bit taller as they reach for any light. Plants in part shade stay a bit more compact and dense. Both spots produce good results but the looks vary a bit by site.
Brunnera spread dimensions matter most for ground cover planning in shade beds. Plant clumps about 24 inches (60 centimeters) apart for a solid cover in three to four years. The leaves will fill in the space and block out most weeds. This spacing gives each plant room to grow without crowding its neighbors at full size.
For accent plantings, you can space brunnera a bit farther apart for distinct clumps. 30 inches (75 centimeters) between plants keeps each clump as a clear focal point. This works well in mixed beds with other shade plants like hostas and ferns. You see each plant as its own piece of the bigger picture.
I learned to plan for the 30 inch spread of mature plants when I first started shade gardening. My early beds had plants too close together and they fought for space within a few years. Now I leave plenty of room between brunnera and other shade plants. The beds look a bit sparse for the first year, but fill in fast by year three.
Edge of bed plantings should sit at least 12 inches in from the lawn edge. The leaves will spill out a bit as the plant grows wider each year. This setup keeps the lawn mower clear of the leaves and stops damage. Plan ahead and your brunnera will have the right space to grow into a full mature plant for years of beauty in your shade beds.
Read the full article: Brunnera Plant Growing and Care Guide
