Daylilies are sturdy, adaptable plants that will grow nearly anywhere with very little effort, as long as they have plenty of bright sunlight. Although daylilies need very little special care, they will continue to bloom at their best and brightest if the plants are divided every few years. Split daylilies by early September, and the roots will have time to establish before winter cold.
Prepare the planting area for the divided daylilies before you begin. It's important that you plant the divided daylilies quickly so the roots don't have time to dry out. Dig out any weeds, and cultivate the area with a shovel or garden fork to a depth of at least 12 inches. Work 3 or 4 inches of peat moss or compost into the top of the soil.
Rake any debris, weeds or mulch away from the daylily plant. This will give you room to work, and will enable you to see where you need to dig. If necessary, cut the outer leaves down to about 6 inches to make the plant more manageable.
Place a garden fork into the ground about 6 to 12 inches from the base of the daylily plant and use the fork to dig 10 to 12 inches into the soil, loosening the daylilly's roots. Repeat as you work in a circle around the plant until the roots are loose, then lift the daylily from the ground. Work slowly and carefully and try to retain as much of the root system as possible.
Separate the daylily plant into two clumps. The easiest way to do this is to put two garden forks back-to-back into the center of the plant, then pull the garden forks in opposite directions. Once you've divided the daylily into two clumps, divide the clumps with your hands, or cut them apart with a sharp knife. Dispose of any dead, weak or spindly areas at the center of the daylily plant.
Dig holes in the prepared area for the divided daylilies. The height of the holes should be a bit less than the daylilies, and twice as wide. Leave at least 18 inches for each plant. If necessary, use scissors to trim the roots back to 8 to 9 inches to make the clumps easier to plant. Don't plant the daylilies with the roots twisted or matted.
Plant the daylilies, and cover the crown of the plant with less than an inch of soil. If the roots are planted too deeply, they can rot.
Water the transplanted daylilies throroughly, and spread an inch of mulch around the perimeter of the plant to retain moisture and keep weeds down. Don't put the mulch on top of the plant, because it can become too hot, and can invite pests and disease. The daylilies shouldn't need to be divided again for another four or five years.