Fall blooming chrysanthemums extend the gardening year to the first frosts, their bright, daisy-like blooms providing generous flower displays. Also called garden mums, hardy chrysanthemums return year after year, requiring minimal attention. Specialist nurseries have bred many chrysanthemum varieties, allowing gardeners a wide choice of color, flower type and plant size. Usually hardy down to U.S. Department of Agriculture (USDA) plant hardiness zone 4 or 5, cold-tolerant varieties are available for zone 3.
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Tall chrysanthemums provide leafy backgrounds to front-of-border flowers during spring and summer, then continue the flowering display in fall. "Emperor of China" chrysanthemum (Chrysanthemum "Emperor of China") grows 3 to 4 feet tall and bears 1 1/2-inch wide, dark-pink centered pink flowers in late fall, and is suitable for USDA zones 4 through 9. For a cooler climate, another tall garden mum is "J. C. Weigelan" chrysanthemum (Chrysanthemum "J. C. Weigelan"). Hardy in USDA zones 3 through 7, this bears 3 1/2-inch-wide, bright red blooms and grows a minimum of 3 feet tall.
One or two compact, hardy chrysanthemums planted toward the front of garden borders provide prominent fall flowers. Chrysanthemum "Sweet Peg" (Chrysanthemum "Sweet Peg"), grows 12 to 18 inches tall and bears pink-purple, 3/4-inch wide blooms. Chrysanthemum weyrichii is smaller, growing 8 to 12 inches tall. This garden mum provides 2-inch wide, yellow-centered, pink or white flowers from late summer to hard frost. For reliably pink or white blooms, plant cultivars "Pink Bomb" or "White Bomb." All plants are hardy in USDA zones 5 through 9.
The University of Minnesota has bred several fall-blooming chrysanthemums to withstand very cold winter weather. Mammoth "Red Daisy" garden mum (Chrysanthemum morifolium "Red Daisy") grows up to 3 feet tall and 6 feet wide after its first year, and bears prolific yellow-centered, deep-red fall flowers that fade to antique rose. Mammoth "Yellow Quill" garden mum (Chrysanthemum morifolium "Yellow Quill") bears interesting tubular-shaped, clear yellow fall flowers, and eventually reaches up to 3 feet tall and 5 feet wide. Both plants are hardy in USDA zones 3 to 9.
Growing on a suitable site, hardy fall-blooming chrysanthemums are low-maintenance plants. Established plants tolerate freezing temperatures, but to give the optimum start, wait until frosts are over before planting young plants in spring. Soil enriched with organic matter, such as garden compost or well-rotted manure, promotes good growth and flowering, and increases drainage, helping prevent plants rotting over winter. Chrysanthemums also need full-sun sites. In mid-July, pinch out new growth and stake plants in danger of falling over. Water during dry weather to keep soil moist.