White perennial flowers include foxgloves, dahlia, columbine, primrose, iris, geraniums, Shasta daisies and carnations. Perennial flowers grow for more than two seasons and frequently go dormant in the winter. Flowering plants that have a dormant season are cut back, or pruned, in the fall. White perennial flowers such as iris and dahlia grow from bulbs and rhizomes. Their green stems, leaves, and flower blooms are left to dry before cutting them back.
Choose which white perennial flowers require cutting back in the fall. White iris have bloomed in spring, been left to dry on the plant, and by fall are ready to be cut. Shasta daisies show their readiness when the tall stems droop and the flowers curl up. Marguerite daisies show signs of wilt and leaves droop when the plant is ready for a pruning trim.
Use garden shears to cut away all deadwood and stems that are not producing leaves and flowers. Bulbs and rhizome plant leaves should be cut back to 3 inches from the ground. Some perennial flowers are getting dry by this time of the year and can be pulled up gently by the stalk. Shasta daisy and white cyclamen separate easily from their root systems when it is time to go dormant. White blooming perennial geraniums do not go completely dormant but perform better if cut back once a year. Cut deadwood and stems to 4 inches from the ground.
Clean up plant debris and put it on your compost pile. Debris attracts insect pests, which weaken new growth in spring.
Use a shovel or trowel to add a portion of compost as a side dressing to each pruned plant. Flowering perennials need nutrients during their dormant season to replenish their growing strength for springtime. Compost provides a steady slow release of nutrients all winter long