Impatiens

A tender perennial from Madagascar grown across temperate North America as a heat-loving summer annual - a mounding 6-18 inch plant in the dogbane family covered in flat five-lobed phlox-like flowers from June to frost. The species blooms rosy-pink to red with a darker mauve throat, and it shrugs off the hot, humid weather that wilts most bedding plants. Every part of the plant is poisonous: it is the natural source of the vinca alkaloids used in chemotherapy.

A compact, frost-tender warm-season annual from Mexico and Central America grown for its dense, fuzzy, thread-like ("flossy") flower clusters - most famously in soft true blue and lavender-blue, the trait that sets it apart from almost every other bedding annual, plus pink and white forms. It mounds into a clumping cushion 6 to 12 inches tall and about as wide, blooming from early summer until frost over soft, heart-shaped, slightly hairy leaves. It is easy and rewarding bedding, edging, and container color in full sun to part shade with steady moisture, but it is strictly look-don't-eat: the foliage and stems contain hepatotoxic pyrrolizidine alkaloids and are toxic if ingested.

A tender perennial from New Guinea grown almost everywhere in North America as a warm-season annual, prized for non-stop bright bloom in part shade - and, unlike common impatiens, in considerably more sun. It mounds 6 to 24 inches tall and 1.5 to 3 feet wide, carrying large, flat, five-petaled flowers in coral, salmon, pink, red, orange, lavender, and white above bold, often bronze-tinted dark foliage. Its real selling point is honest and practical: Impatiens hawkeri is resistant to impatiens downy mildew (Plasmopara obducens), the disease that collapsed plantings of Impatiens walleriana, making it the dependable shade-to-part-sun bedding plant where the common species can no longer be trusted.

The garden petunia is a complex Brazilian-derived hybrid in the nightshade family, grown almost everywhere as a warm-season bedding annual for its funnel-shaped, often fragrant flowers in nearly every color except true brown and black. Missouri Botanical Garden ranks it second only to impatiens in annual bedding-plant sales, prized for non-stop bloom from late spring until frost. It is a tender perennial hardy only in USDA Zones 10-11, so most of North America treats it as a single-season annual.

Common houseleek, or hens-and-chicks (Sempervivum tectorum), is an evergreen alpine succulent that forms tight rosettes of fleshy, pointed leaves, each rosette (the "hen") ringed by smaller offset rosettes (the "chicks") on short runners. Barely a few inches tall, it spreads into a low mat and thrives in the harshest hot, dry, sharply drained spots: gravel, walls, sink gardens, and the tiled roofs it was once planted on. In summer a mature rosette sends up a stout stalk of star-shaped reddish-purple flowers, then that rosette dies, leaving its chicks to carry on. It is one of the toughest, most cold-hardy, most forgiving plants there is, asking only for sun and drainage and resenting nothing so much as wet, rich soil.

Bergenia cordifolia (often treated by botanists as a synonym within B. crassifolia) is a tough, evergreen perennial native to the Altai Mountains, southern Siberia and Mongolia, grown for its bold, heart-shaped leathery leaves that flush red-bronze through winter and its deep pink flower spikes in early-to-mid spring. It is one of the most tolerant groundcovers in cultivation - enduring deep shade, poor soil, drought, and hard continental cold (commonly rated to USDA Zone 3 in US horticulture; RHS rates it H7, hardy below -4°F). The honest catch is its shallowly creeping rhizomes: in mild, moist climates they can colonise well beyond the intended planting, and the large, persistent leaves trap fallen debris and are notoriously attractive to slugs and vine weevils.