Lilies, belonging to the genus Lilium, are celebrated for their elegant flowers and often intoxicating fragrance, but they require specific seasonal preparation to ensure their survival through cold weather and guarantee a vibrant rebloom. These true lilies, distinct from plants like Calla or Daylilies, are temperate bulbs that enter a period of cold dormancy. Overwintering successfully requires understanding the bulb’s needs and providing the proper environment, whether through protection in the soil or indoor storage.
Preparing Lilies for Cold Weather
The transition into winter dormancy begins well before the first hard freeze, focusing on maximizing nutrient return to the bulb. Do not cut back the foliage immediately after the flowers fade; the leaves must be left intact until they naturally yellow or brown. This color change signals that the plant has finished photosynthesis, transferring energy reserves down to the underground bulb for winter storage.
Once the stems have completely withered, typically in late fall, cut them back to just an inch or two above the soil surface. Use clean, sharp pruning shears to minimize the risk of introducing pathogens into the remaining stem and bulb. Clear away any remaining plant debris, spent stalks, and fallen leaves from the surrounding soil. This sanitation step removes potential overwintering sites for pests and fungal spores that could otherwise cause rot or disease during the dormant period.
Cease all fertilization as the growing season concludes in late summer or early fall. Introducing nitrogen at this point encourages tender new growth that is highly susceptible to frost damage. Watering should also be diminished, especially in regions with high autumn rainfall, as wet, cold soil is a primary cause of bulb rot.
Overwintering Hardy Lilies In-Ground
Most true lilies, including common Asiatic and Oriental hybrids, possess a high degree of cold tolerance, surviving comfortably in United States Department of Agriculture (USDA) Hardiness Zones 3 through 9. For these hardy varieties, the goal is not to keep the soil warm, but to provide insulation that stabilizes soil temperature and prevents damaging freeze-thaw cycles. These constant fluctuations can heave bulbs out of the ground, exposing them to lethal cold and desiccation.
The protective layer should only be applied after the ground has frozen solid or a few weeks after the first hard frost, typically when temperatures consistently drop below freezing. Applying mulch too early can trap warmth, delaying dormancy and making the plant vulnerable to a sudden, deep freeze. A layer of organic material between four and six inches deep provides sufficient insulation.
Suitable mulching materials include loose items like straw, shredded hardwood leaves, or pine needles, which trap air and allow for good drainage. The mulch should cover the entire planting bed and extend six to twelve inches past the perimeter of the plant clump. This insulation helps delay the deeper ground freeze and prevents premature sprouting if a mid-winter warm spell occurs.
Lifting and Storing Tender Lilies
Certain lily species, or lilies grown in zones colder than their established hardiness range, may require lifting and indoor storage to survive the winter. This process must be completed before the ground freezes solid, but ideally only after the foliage has died back naturally or after a light frost has killed the top growth. The bulb must be carefully excavated with a garden fork, starting several inches away from the stem to avoid damaging the delicate, tunic-less bulb scales.
Once lifted, excess soil should be gently removed, but avoid washing the bulbs unless necessary, as excess moisture encourages rot. The bulbs then require a curing period, which involves drying them for a few days in a cool, dark, and well-ventilated area, often at a temperature between 60 and 70 degrees Fahrenheit. After curing, inspect the bulbs for any signs of damage or decay, discarding any that are soft or moldy.
For storage, the bulbs need a medium that prevents desiccation while still allowing air circulation, as lily bulbs lack the protective outer layer found on tulips or daffodils. They should be nestled into a breathable material like slightly moist peat moss, vermiculite, or sawdust.
Place the bulbs in a ventilated container such as a cardboard box or paper bag. The ideal storage location is a dark, dry space where the temperature is consistently cool, typically ranging between 35 and 45 degrees Fahrenheit. This could be a cold basement or unheated garage that stays above freezing.