The heady fragrance of traditional Easter lilies (Lilium longiflorum) or Madonna lily (Lilium candidum) is never forgotten once experienced. Both are true members of the lily family. They grow about 1-1/2 to 3-1/2 feet tall in full sun in rich, evenly moist but well-drained soil. Because you are asking about planting outside in zones 5 and 6, you’ve probably heard numerous stories of how people have a whole garden full of “Easter lilies” that they’ve planted every year and successfully had them grow and bloom repeatedly.
That being said, a few words of caution and qualification go with those success stories. The lily hybrids of Lilium longiflorum are not usually considered a garden plant, being normally hardy to only zones 7 to 9. Consequently they are grown primarily in pots here, and nurseries force them in bloom so their buds burst forth in time for the Easter celebration. Remember this observance moves on the calendar annually, from as early as mid-March to as late as mid-April. The bulb is not mysteriously intelligent; it has just been manipulated by greenhouses to bloom at the desired time.
That being said, there is a cultivar called ‘Mount Everest’ that bears fragrant white trumpets and can be grown in the ground in zones 5 to 8. If you were fortunate enough to receive or purchase a lily with an identification tag, you may know if you have that plant or another named cultivar. Or, if you in fact have a Madonna lily, it will tolerate temperatures down to 25 degrees. Unfortunately most Easter lilies rarely get tagged because they are either forced in a greenhouse or shipped in from warmer regions and are not hardy to our zones that deal with frozen soil in winter.
However, if you would like to attempt to save it in the ground, choose a sheltered, sunny spot that is well-drained. Many times we have microclimates around our homes, especially near the house foundation, that mimic a zone or two warmer than our overall region. If that warm, dry place is close to an often-used walkway, all the better to enjoy the fragrance.
Plant the bulb about 6 to 8 inches down, as you would any of the hardy summer-blooming Asiatic or Oriental lilies. Add about a tablespoon of granular bulb fertilizer to the planting hole. Evenly moist but well-drained soil at the site, especially in winter, cannot be stressed enough. You can leave the foliage intact to help feed the bulb naturally until the leaves completely brown out. Apply a heavy blanket of shredded leaf mulch to the planting area to minimize winter temperature fluctuations.
If there isn’t a place in your yard that suits these special conditions, try letting the foliage die back with the bulb in the pot. Let the soil dry out, and then lift the bulb, checking for soft spots. Make sure it is dry and soil-free. Store the bulb wrapped in a paper bag in a cool dry place until the following February. You are mimicking the winter dormancy of its native habitat. Then you can pot it up with a well-draining soil mixture, keeping the soil moist but not soggy. Put it in a warm, sunny window away from drying heat vents and watch the bulb come to life.