What Are the Causes of Mum Blooms Turning Brown?

Disease

• Shasta daisy mums may get a disease called Alternaria leaf spot. The blossoms sometimes turn brown and die off sooner than usual, and light and dark circles and brown spots sometimes appear on the leaves as well. Various rust diseases and Botrytis, a fungal disease, also turns infected areas, including blossoms, from brown to dark brown, starting in one spot and spreading over the flower. Fusarium wilt also causes mums to turn brown and die one at a time or entirely. Most diseases are remedied with proper watering and fungal or sanitation treatment.

Poor Conditions

• An unhappy brown mum may be living in less than ideal conditions. Using too much fertilizer or the wrong balance can burn plants, including their blossoms. Keeping mums in their original pot can also cause drying and browning. The roots become cramped, and you typically see them sprouting out the bottom or near the top of the pot. Mums are fairly drought resistant, but they do need irrigation in dry climates. Mums need soil to remain moist but not wet.

Overgrowth

• Chrysanthemums grow tall and will overgrow unless you pinch the tops during the growing season. Lower leaves and blossoms may brown when this happens, since they aren't getting enough light. Pinching the plant creates a more compact growth habit with healthier and more prolific blooming. When new shoots grow during the summer, pinch off the tops and leave two to three leaves. Do this about once a month until late summer. Toward the end of the summer, mums should be left to grow naturally so flower buds will form.

Normal Life Cycle

• Mums are widely grown as annuals, so a frost will kill them. If it's mid- to late fall, and you've already experienced low temperatures or a frost in your area, this could be why the mums are turning brown. Cut off the plant and leave the roots in the ground to see if it will come back next season, covering it with 3 to 5 inches of mulch. Otherwise, remove the roots from your garden and plant new flowers next year.