Pansies (Viola x wittrockiana) are the reliable standbys for cool-weather blossoms. Their engaging "faces," or top petals, come in bold or pastel colors. Remove spent flowers to promote repeat blooming. Although they're technically perennials, pansies tend to be short-lived because they don't tolerate heat well (some varieties are more heat-tolerant than others). Pansies will bloom all winter in warmer climates.