Beloved for late summer and fall bloom,Chrysanthemum once included around 160 species, but taxonomists have moved the vast majority to other genera.
Chrysanthemums bred for the cut-flower industry, for forcing in pots (and sold in bloom every day of the year), and for exhibition are primarily florists’ chrysanthemums. Some of these also make good garden subjects, as do all C. weyrichii and C. zawadskii selections. You may also find excellent hybrids between C. zawadskii and C.x grandiflorum called rubellums.
Chrysanthemum x grandiflorum
The most useful of all autumn-blooming perennials for borders, containers, and cutting, and the most versatile and varied of all chrysanthemum species, available in many flower forms, colors, plant sizes (from under a foot to 6 ft. tall), flower sizes, and growth habits. Colors include white, yellow, red, pink, orange, bronze, purple, and lavender, as well as multicolors.
Garden culture. It’s easy to grow chrysanthemums, not so easy to grow prize-winning chrysanthemums. The latter need more water, feeding, pinching, pruning, grooming, and pest control than most perennials. Plant in early spring, in an area away from large trees or hedges with invasive roots. In hot climates, choose a spot shaded from afternoon sun. Dig organic matter and a complete fertilizer into good, well-drained garden soil 2 to 3 weeks before planting.
Water deeply at intervals determined by your soil structure—frequently in porous soils, less often in heavy soils. Too little water causes woody stems and loss of lower leaves; overwatering causes leaves to yellow, then blacken and drop. Feed in-ground plants two or three times during the growing season. Make the last application with low-nitrogen fertilizer not less than 2 weeks before bloom.
Frequent pinching produces sturdy plants with big flowers. Begin at planting time by removing the plant tip. Lateral shoots will form; select one to four of these for continued growth. Keep pinching all summer, nipping the top pair of leaves on every shoot that reaches 5 in. long. Stop pinching earlier in coldest regions. For huge blooms (on large-flowered sorts), disbud (remove all flower buds except one or two per cluster).
Stems are attacked by borers in desert areas. Aphids are the only notable pest in all areas. One way to avoid them is to feed plants with systemic insecticide/ fertilizer combination.
Stake taller plants as needed to keep them upright. After bloom, cut back plants to within 8 in. of the ground. Where soils are heavy and likely to remain wet in winter, dig clumps with soil intact and set on top of ground in an inconspicuous place. Cover with sand or sawdust if you wish (a good idea in Zones 2, 3, and 10). Take cuttings from early to late spring (up until May for some varieties) or when shoots are 3–4 in. long. As new shoots develop, you can take additional cuttings from them. In cold-winter areas, store in a cold frame or mulch with light, noncompacting material like excelsior.
Pot culture. Pot rooted cuttings midwinter to early spring, using porous, fibrous, moisture-holding planting mix. Move plants to larger pots as growth requires—don’t let them become root-bound. Pinch and/or stake as required. Plants need water daily in warm weather, every other day in cool conditions. Feed with liquid fertilizer every 7 to 10 days until buds show color.
Off-season, potted chrysanthemums. Florists and even grocery stores sell potted chrysanthemums in bloom every day of the year, though by nature a chrysanthemum blooms in late summer or fall. Growers force these plants to bloom out of season by subjecting them to artificial day lengths, using lights and dark cloths. You can plunge the potted flowering plants right into a garden bed or border for an immediate (but expensive) display, or enjoy them in the house while the flowers remain fresh and then plant them out. Either way, they will not bloom again at the same off-season time the next year. Instead, they will revert to their natural inclination and commence fall bloom once again.
To pot off-season mums after bloom, cut off flowers when they fade, leaving stems 6–8 in. long. Remove the soil clump from the pot and break apart the several individual plants that were grown in the pot. Plant these individual plants. When new growth shows from the roots, cut off the remainder of the old flower stems.