Daylilies are one of those flowers you can plant in your garden and never have to worry about. They seem to grow and produce gorgeous flowers regardless of the soil conditions or the amount of watering they receive. The only thing you might have to do once in a while is thin them out because they will slowly fill up the space you planted them in, continuing to spread year after year. You can easily remedy this by digging up the mass of roots, separating the tubers, and replanting them with plenty of room to spread out.
In late summer or early fall, at or after the end of the growing season, trim back the patch of daylilies that you want to thin out by cutting the green blades to six inches above the soil line. This will make the job of thinning much easier since the grassy portion of the lilies can become tangled. You can trim a very large patch by running over it with your lawn mower set at the highest setting. Rake up the debris and put it in the compost heap.
Dig your fork into the ground about six inches out from the edge of the patch of daylillies and down as deep as you can with your weight stepping on the heel of the fork. Pull back and down on the fork handle so that the soil is lifted up when the tines come to the surface. You'll be able to see how all the tubers have grown together, forming a mat of roots. You may have to dig around the clump in several places before you can lift the matted tubers out of the ground.
Separate the tubers by shaking off the dirt and carefully separating the roots that are holding the mat together. Large patches may require you to cut through the mass of roots with a landscaping shovel and remove large sections. For smaller gardens, set aside one tuber for every six square inches of space you want to fill. Throw the rest of the tubers into a bucket to be planted elsewhere or given away.
Replant the tubers with the leafy part sticking up just at the soil line. You can add more composted dirt at this point to refresh the soil and revitalize the plants. Make sure you keep them at least six inches from each other or you will be thinning them again in 2 years instead of 4 or 5. Tamp the soil down over the tubers to make sure they have good soil contact.
Add a 3- to 4-inch layer of mulch over the bed to conserve moisture and improve the area's appearance—it will look better if the old growth is totally covered under the mulch. Within a week you will see new green shoots popping through the mulch. Allow them to grow until the frost kills them, at which point you can trim them down to just below the mulch.