Common zinnia

A compact, mounding deciduous shrub bred in the 1930s by crossing the East Asian species Caryopteris incana (southern China, Taiwan, Korea, Japan) and C. mongholica (Siberia, Mongolia, northern China) - it has no wild range of its own. Its defining virtue is a flush of vivid blue-to-violet flowers on the current year's growth in late summer and early fall, a period when little else in the garden blooms, combined with aromatic gray-green foliage and exceptional drought tolerance once established. The honest catch is its borderline hardiness at the cold edge of its range: in zones 5–6 the woody stems routinely die to the ground in winter and the plant resprouts from the base each spring, behaving more like an herbaceous perennial than a shrub - gardeners in those zones should hold back pruning until new growth confirms the crown has survived.

A dwarf, evergreen Mediterranean sub-shrub with intensely aromatic silver-grey needle-like leaves and clusters of small, long-lasting yellow button flowers in summer. Native to the dry, rocky ground of the western and central Mediterranean basin, it is prized for its bold textural foliage and the illusion of a curry scent - although the plant has no culinary relationship to curry spice and its flavor largely disappears on cooking. The honest catch is hardiness: Helichrysum italicum is reliably winter-hardy only to about USDA Zone 8 (around 10°F); in colder climates it either dies outright or must be overwintered frost-free, and even within its range it is short-lived on heavy, wet soils where winter root rot claims it quickly.

Grecian horehound (Ballota pseudodictamnus, accepted name Pseudodictamnus mediterraneus) is a compact, mound-forming evergreen subshrub native to dry Mediterranean regions of southern Greece, Crete, southwest Turkey, northeast Libya, and northwest Egypt, where it grows on rocky, sun-baked slopes. Its nearly circular, silver-felted leaves and small pink late-spring flowers (largely hidden among the foliage) earn it a place in any drought-tolerant planting, and it holds the RHS Award of Garden Merit. The honest catch is hardiness: while it tolerates brief dips to around 14°F (USDA zone 7b), prolonged wet cold kills it reliably, so in climates with cold, wet winters it must have razor-sharp drainage or it rots at the crown - a combination of frost and wet soil is almost always fatal.

Aubrieta (Aubrieta deltoidea) is a low, mat-forming evergreen perennial in the mustard family (Brassicaceae), native to the rocky hillsides of southeastern Europe - primarily Greece, the Aegean Islands, Crete, and adjacent Mediterranean coasts. It is one of the most reliable spring-flowering ground covers for sunny, well-drained spots: cascading sheets of violet to deep pink four-petalled blooms from March through May, attractive to bees and bee flies. The honest catch is that without a hard cut-back immediately after flowering, plants become woody and bare in the centre within two or three years, collapsing from a tight carpet into a tired, gappy mat.

Felicia amelloides is an evergreen, woody-based perennial subshrub native to a narrow coastal strip of South Africa's Western and Eastern Cape, where it colonises stabilising sand dunes, sandy flats, and rocky outcrops at 0 to 3,280.8 feet. In the garden it delivers a near-continuous flush of sky-blue, yellow-centred daisy flowers on neat mounding growth, typically 12 to 24 inches but capable of reaching about 3.3 feet, making it one of the few true blue-flowered plants for sunny pots and borders. The honest catch is frost-tenderness: it survives only light frost in sharply drained soil and collapses below about 23°F, so outside USDA zones 9-11 it must be overwintered under glass or replaced annually - a real commitment in cool-temperate gardens.

Campanula carpatica is a low, mounding herbaceous perennial native to the rocky subalpine habitats of the Carpathian Mountains, ranging across Poland, the Czech Republic, Slovakia, Romania, and Ukraine (Wikipedia). Its wide, upward-facing bell flowers in violet-blue, white, or pink appear from June through August, making it one of the longest-blooming edging perennials available, and it holds an RHS Award of Garden Merit. The honest catch is longevity: it tends to behave as a short-lived perennial, often thinning or declining after a few seasons, so gardeners should plan for regular division or fresh plants from seed to hold the planting.