Asiatic lilies look exotic and tropical but are hardy staples even in northern gardens. They make lovely cut flowers and provide a broad range of colors to the garden palette. When the bloom is done, however, the foliage can begin to fade, dry out, and die, tempting gardeners to cut the plant to the ground. Care and restraint are called for, however, if you want your lilies to to be strong and beautiful next year.
Storing Food for Next Year
Because lilies store food for the next year's growth in their bulbs underground, the current year's leaves are vital to the next year's bloom. Long after the blooms have faded, dried out, and dropped their petals, the leaves and remaining living tissue are taking in sunshine and, through photosynthesis, making food for next year's flowers and storing it underground. For the best, healthiest, most spectacular lilies next year, every bit of above-ground plant tissue must be preserved so it can do that work.
Breaking off spent blooms prevents the plant from making seeds. Because seed production diverts some of the plant's energy resources away from storage, deadheading lilies is a good practice. However, even in this, it pays to be conservative. Take only as much stem as you absolutely must. If you decide to pick a few stems for a bouquet, keep in mind the plant's food-storing needs, too. Take one stem each from several plants rather than several stems from one plant. Leave at least half the leaves and stems on each plant; two-thirds is better.
Resist the temptation to stake or wrap the foliage to disguise its increasingly bedraggled appearance. Because overlapped leaves will get less sun, their photosynthesis capabilities will drop.
Once a leaf, section of leaf, or stem dries out completely and becomes yellow and brittle, it's OK to cut away that section, but only that section, to improve the plant's appearance.
Once the plant is hit with a killing frost, photosynthesis is over for the season, and so the plant can produce and store no more food. You can then cut the remaining foliage down to the ground as part of your fall garden cleanup