If you cut true lilies back to the ground you would have no foliage left, since the foliage on a true lily grows from the lily stalk. As was mentioned by daylilydayzed, daylilies do not grow from bulbs - only true lilies do. True lilies should be trimmed (after blooming) so that 2/3 of the stem is still standing.
http://forums.gardenweb.com/discussions/1948695/cutting-back-foliage
Tip. 1  Daylilies are occasionally infested with mildew or insects in summer. Cut back badly affected plants to within 6 inches of the ground. 2  Divide the daylily bulbs every five to seven years. Dig and divide after the foliage dies in fall or before new growth begins in spring.
http://homeguides.sfgate.com/trim-daylily-leaves-22696.html
Daylilies are a perennial flower with bright blooms that appear amidst sword-like leaves throughout the summer. In order to protect daylilies so that they come back each year, it is best to cut them back. Daylilies begin with the tips of green fronds emerging from the soil in early spring.
http://agriviet.net/20908-when-should-daylilies-be-cut-back/
gailwrite(6KY) Purists will have a fit, but I cut my daylilies down to the ground, feed them and keep them watered, they grow back before fall and I have fabulous day lilies every year. Otherwise, they mess up the garden with dying foliage. Like Bookmark July 19, 2012 at 8:39PM.
http://forums2.gardenweb.com/discussions/1654593/when-do-you-cut-back-daylilies
When daylilies are sent through the mail, they are cut back to about 5-6, and when planted, they sometimes lose the original foliage, and new foliage sprouts from the crown. I don't know where you are in zone 5, but you should have a few weeks of growing weather left before the ground freezes, so maybe there's hope.
http://forums.gardenweb.com/discussions/1948695/cutting-back-foliage
Once the leaves have begun to droop and turn brown you can cut back your daylilies using simple garden shears and cutting them off at ground level. This is also the best time to thin or move your daylilies. There is no need to dig up daylilies for the winter. Simply cut them back and cover them with compost and mulch.
http://agriviet.net/20908-when-should-daylilies-be-cut-back/
Site and soil. Daylilies grow best in full sun. They will tolerate light shade, but flower best with a minimum of six hours of direct sun. Light shade during the hottest part of the day keeps the flowers fresh. Daylilies should not be planted near trees and shrubs that are likely to compete for moisture and nutrients.
http://www.extension.umn.edu/garden/yard%2Dgarden/flowers/growing-daylilies/
After your day lily flowers fade, leave the foliage. Cutting back the plant in an effort to tidy up the garden can weaken your day lilies. The leaves of the day lily photosynthesize to provide food for the roots. This builds up the roots to strengthen them to survive the winter and to grow again the following year.
http://homeguides.sfgate.com/happens-cut-down-day-lilies-early-76673.html
Daylilies are occasionally infested with mildew or insects in summer. Cut back badly affected plants to within 6 inches of the ground. The plants grow back healthy foliage and usually resume blooming within four weeks. Divide the daylily bulbs every five to seven years. Dig and divide after the foliage dies in fall or before new growth begins in spring.
http://homeguides.sfgate.com/trim-daylily-leaves-22696.html
Transplant Trimming. Just after the flowers fade in late summer or early fall is the optimal time to divide and transplant day lilies. Before the move, cut the foliage back to 6 to 8 inches high. This makes the plant easier to work with while still leaving enough foliage to provide energy to the roots.
http://homeguides.sfgate.com/happens-cut-down-day-lilies-early-76673.html
when to cut back daylilies foliage
Cut back a day lily, foliage within 6 inches of the ground.