The variety of available colors combined with low maintenance makes daylilies popular among gardeners. However, their roots spread in a weed-like manner causing new plants to sprout next to the old ones. Controlling daylilies is a matter of planning and regular maintenance.
Controlling daylily spread prevents other ornamental plants situated nearby from becoming starved of nutrients from the crowding. Further, fewer daylilies means more delicate plants have an easier time establishing roots as there is less competition in the soil.
Daylilies can be controlled by confining them inside permanent barriers (such as a flower bed surrounded by cement), planting them in containers, and thinning out their roots.
According to "The Southern Living Garden Book" crowded plants should be thinned every three to six years. Dig them up with a pitchfork and divide them at the roots. Replant some of the smaller clumps and give some away if desired.
Avoid having to remove daylilies after they have become established by only planting them in areas where spreading would be desirable.
Removing daylilies by trying to pull them out by their leaves is unwise. The roots are invasive and if you leave even small fragments underground new plants can form. Dig up the entire clump with a shovel.