Excess nitrogen will increase foliage growth at the expense of flowering. Deadheading or removing spent flowers will promote longer flowering. Unless collecting seeds for planting, also remove seedpods so energy will go into the blooms the following year. Daylilies will continue to flower even during the heat of summer when other flowers may slow down. However, they will benefit from an occasional watering during the growing season, especially during extended dry periods.
Daylilies also respond favorably to additional moisture before bloom.
Perennial grasses that become established in daylily clumps can be difficult to eradicate. A pre-emergence herbicide containing trifluralin or pendamethalin will help control some broadleaf and grassy weeds in daylily beds. For current herbicide rates and other information, read the herbicide label. Mulching two to three inches deep also will help eliminate some weed problems. Elbert C. Dickey, Interim Dean and Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.