The various Colorado regions have different climates and growing conditions. While the prairies experience a temperate climate, the valleys have a semi-arid climate. Mountain areas are alpine. Colorado falls within the United States Department of Agriculture (USDA) Hardiness Zones 2 to 7. Colorado gardeners should select flowers according to appropriate zone, flower color, bloom time, intended use and mature plant size.
The marsh marigold (Caltha palustris), an herbaceous perennial in the buttercup family (Ranunculaceae), prefers organic soils in marshy areas. This flower features dark green leaves and yellow, waxy flowers that bloom from April through June. Marsh marigolds reach from 12 to 18 inches in both height and spread. Rust and powdery mildew sometimes affect this plant. Colorado gardeners often use marsh marigolds in water gardens, bog gardens and pond margins.
The friar's cap (Aconitum napellus), a perennial member of the Ranunculaceae plant family, earned its name due to the hood-shaped, blue-purple flowers that appear in late summer. Mature plants reach from 2 to 4 feet in height and 12 to 18 inches wide. All parts of the friar's cap plant contain toxic principles. This plant is also called wolfsbane since the toxins were once used to kill wolves. The friar's cap grows best in moist, well-drained soils that receive at least partial sun. Verticillim wilt and crown rot sometimes occur. Friar's cap plants work well in continuously moist soils along ponds, streams or water gardens.
Fan columbine plants (Aquilegia flabellate), herbaceous perennials in the buttercup family, naturally occur in Japan but grow well in Colorado climates. Mature plants form clumps reaching between 6 and 9 inches in both height and spread. Fan columbines bear fan-shaped leaves and light blue flowers that bloom in May and June. This plant prefers moist, well-drained soils in partly to fully shady locations. Leaf miners often feed on the foliage. Fan columbine flowers perform well in rock gardens, naturalized areas, cottage gardens and borders.
Siberian bugloss (Brunnera macrophylla) belongs to the borage family (Boraginaceae) and grows well in moist, rich soils that receive partial shade. This perennial forms clumps ranging from 12 to 18 inches high and 18 to 36 inches wide. Siberian bugloss flowers bloom in April and May, featuring blue petals with yellow centers. Snails and slugs occasionally feed on the heart-shaped, black-green leaves. Colorado gardeners often plant Siberian bugloss in borders and woodland gardens.
The bellflower (Campanula persicifolia), also called the willow bell, reaches up to 36 inches in height and 18 inches wide. This member of the Campanulaceae family features bell-shaped, white or blue flowers that bloom in June and July. The bellflower prefers medium moist, well-drained soils in partly shady to fully sunny locations. This perennial plant sometimes suffers from aphid infestations. Bellflowers work well when mass planted in cottage gardens and borders.