Grasses thicken and provide better cover when regularly clipped at the proper height. Prune rhododendrons after they flower. On young and old plants, snap off spent flower stalks by bending them over until they break away from their stems. Be careful not to damage growth buds at the base of each flower stalk. Don't trim iris leaves into scallops or fan shapes after the flowers fade.
Leaves carry on photosynthesis and develop nourishment for next year's growth.
Cut off brown tips and remove the flowering stalk down to the rhizome. If you're dividing irises, cut the leaves back by about half just before you move them. If you're growing plants outdoors in containers, don't use a soilless potting mix. Be sure it contains at least half soil. Or make your own blend for window boxes and patio containers by mixing one part compost, one part garden soil, and one part builder's sand.