Grace Ward Lithodora (Lithodora diffusa ‘Grace Ward’) is a favored groundcover known for its vivid blue flowers and evergreen foliage. It is a popular choice for rock gardens, borders, and as a cascading element in landscapes. Many gardeners wonder if its vigorous spreading habit means it is an invasive species, prompting a closer look at its growth characteristics and ecological impact.
Understanding Invasive Versus Spreading
An “invasive species” is a non-native organism that causes environmental or economic harm, or harm to human health. Such plants often reproduce rapidly, lack natural predators, and can outcompete native flora, disrupting local ecosystems. They might produce many seeds, possess aggressive root systems, or release chemicals that hinder the growth of surrounding plants.
Invasive plants are often introduced by human activity. They establish quickly in disturbed soils and spread over vast distances, leading to significant ecological shifts. In contrast, a “spreading” or “vigorous” plant grows enthusiastically in a garden without posing a broader ecological threat. These plants may require management to maintain their desired size or location, but they do not escape cultivation to colonize wildlands or displace native plant communities.
Grace Ward Lithodora’s Growth Characteristics
Grace Ward Lithodora is not classified as an ecologically invasive plant. It is a vigorous, mat-forming evergreen shrub with a prostrate, spreading habit, typically reaching 6 to 12 inches high and spreading 2 to 6 feet wide. This plant spreads by rooting along its trailing stems, forming a dense groundcover. While it can spread enthusiastically within a garden bed, it generally remains contained within cultivated areas and does not pose a threat to natural ecosystems.
Its vibrant, deep blue flowers appear from late spring through summer, with sporadic blooms into fall. It prefers well-drained, acidic soil and thrives in full sun, though it appreciates some afternoon shade in hotter climates. Its growth is moderate to slow, and it is generally deer-resistant and easy to care for. While it may self-seed in ideal conditions, this rarely leads to widespread colonization beyond the cultivated garden.
Managing Vigorous Growth
Its vigorous, spreading nature means gardeners may need to manage its growth. Regular pruning is an effective method to maintain its shape and size. Trimming after its main flowering flush in late spring or early summer encourages bushier growth, a tidier appearance, and further blooms.
If the plant spreads beyond its intended area, its trailing stems can be trimmed or lifted. Division of mature plants in spring or fall can also help control their spread and provide new plants. For containment, installing physical barriers like edging can restrict its outward growth. Ensuring proper spacing during planting, typically 2 to 3 feet apart, allows the plants to fill in without immediately overcrowding.