Heather is a low-growing evergreen shrub that brings year-round texture and often vibrant color to the landscape. The common name refers to two distinct but related genera: Calluna and Erica. Understanding that growth size is highly variable and depends on both the plant’s specific type and its environmental care is important for successful cultivation. Different species and cultivated varieties, known as cultivars, exhibit a wide range of mature heights and spreads, making the selection process important for achieving a desired garden effect.
Understanding the Two Main Types of Heather
Heather belongs to two genera within the Ericaceae family: Calluna (Scotch Heather or Ling) and Erica (Heath). Calluna vulgaris is the sole species within its genus, typically flowering in the summer and autumn months. This type is recognized by its small, scale-like leaves and tends to form dense, low-mounding habits.
The Erica genus, often called “heath,” contains over 800 species and offers a much wider spectrum of growth habits and sizes. Many popular varieties of Erica are winter- or spring-blooming, such as Erica carnea and Erica × darleyensis, providing color during colder months. While both types generally thrive in acidic, well-drained soil, the number of Erica species means their mature dimensions vary more dramatically than the more uniform Calluna.
Size Variation Among Cultivars
Heather size is determined by its cultivar, with mature dimensions generally reached after three to five years of growth. These mature sizes are often categorized to help gardeners select the right plant for their space.
Dwarf Cultivars
Dwarf cultivars, such as Calluna vulgaris ‘Foxii Nana’ or Calluna vulgaris ‘Sister Anne’, typically remain very low, growing to a height of less than 6 inches. They are perfect for rock gardens or as dense groundcovers.
Medium and Large Cultivars
Medium or Standard cultivars make up the largest group, reaching heights generally between 6 and 18 inches, with a similar spread. Cultivars like Calluna vulgaris ‘County Wicklow’ and Erica carnea varieties form substantial mounds suitable for mass plantings. Upright or Large varieties can grow taller, sometimes reaching heights of 18 to over 30 inches. Some Erica species, known as “tree heaths,” such as Erica arborea, can even develop into large shrubs or small trees, reaching heights of four to six feet or more in favorable conditions.
Factors Influencing Final Size
The final size a heather plant achieves is a result of its genetic potential interacting with specific environmental variables. Light exposure is a major factor, as heather performs best in full sun, which encourages dense, compact growth. Plants grown in excessive shade will often become “leggy,” stretching their stems out in search of light, resulting in a less dense habit and reduced size potential.
Soil composition is important, as most heather requires acidic soil, ideally with a pH of 6.5 or less. Alkaline soil restricts the plant’s ability to absorb necessary nutrients, stunting its growth and preventing it from reaching its maximum size. Well-draining soil is required, because poor drainage and waterlogged conditions cause root rot, severely limiting the plant’s growth and survival. Climate and hardiness also play a role, as extreme temperatures or hardiness zone mismatches can limit the plant’s overall maturity and longevity.
Managing Heather Size Through Pruning
Pruning is the most direct way a gardener can control and maintain heather size and shape, while also promoting dense, healthy growth. This annual trimming is necessary to prevent the plant from becoming woody and straggly, which results in bare lower stems and reduced flowering. The correct timing for pruning is immediately after the plant has finished flowering, which varies depending on whether it is a summer-blooming Calluna or a winter-blooming Erica.
The technique involves lightly shearing the plant, removing the faded flower spikes and only a few inches of the current season’s green growth. It is important to never cut back into the brown, old wood, as heather does not reliably regenerate or sprout new growth from this older tissue. For severely overgrown or woody plants, rejuvenation pruning is often unsuccessful, and it is usually recommended to replace the specimen with a younger plant to maintain the garden’s desired scale.