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Hyssops are great for adding height to a border with whorls of long-lasting tiny flowers arranged like a bottlebrush and pointed aromatic fresh green leaves that are attractive to butterflies. They are short-lived though and may need replacing every few years especially after a cold or wet winter. 'Black Adder' has smoky violet flowers on long spires from July to October. Try it as part of a Mediterranean scheme or in a sunny well-drained border among ornamental grasses.

• Garden care: Don't cut back the faded flower-stems until early spring as they provide interest in the winter months. Lift and divide congested colonies in spring.