Lilies are a popular choice for many gardeners, gracing landscapes with vibrant blooms and delightful fragrances. To ensure these plants thrive year after year, understanding their cold tolerance is important. While many lily varieties exhibit impressive hardiness, their ability to withstand winter conditions varies significantly depending on several factors. This knowledge helps gardeners provide appropriate care and protection.
Understanding Lily Cold Hardiness
The extent to which a lily can tolerate cold largely depends on its specific type and native origins. Asiatic hybrids, for instance, are known for their robust cold hardiness, capable of enduring temperatures as low as -35°F (-37°C) and thriving in USDA Zones 3 through 8. Oriental lilies, while also resilient, are hardy to about -25°F (-32°C), fitting within Zones 4 through 9. Trumpet lilies show hardiness in Zones 4 through 9.
Lilies are herbaceous perennials that require a period of cold dormancy to prepare for the next growing season and produce healthy blooms. Winter temperatures should remain below 32°F (0°C) for adequate dormancy, though temperatures up to 40°F (5°C) are also suitable. Unseasonably warm spells during winter can cause premature sprouting, leaving new growth vulnerable to subsequent frosts.
Beyond genetic hardiness, soil conditions play an important role in a lily’s ability to survive cold. Lilies require well-drained soil to prevent their bulbs from rotting. Wet, heavy soils that freeze and thaw repeatedly can lead to bulb decay, making the plants more susceptible to cold damage. Amending heavy clay soils with organic matter like compost or coarse sand can improve drainage, creating a favorable environment for lily bulbs.
Protecting Lilies from Freezing Temperatures
Applying a layer of organic mulch over lily beds in late fall is an effective method for winter protection. Materials such as straw, shredded leaves, or wood chips insulate the soil, helping to maintain a consistent temperature and protecting bulbs from severe freezes. A 2-4 inch layer of mulch is recommended, but in colder climates (below -10°F/-23°C) or for Oriental and Trumpet lilies, an 8-12 inch layer of fluffy material can provide better insulation, especially if natural snow cover is inconsistent. Apply mulch after the ground has frozen solid, typically after several hard frosts, to prevent a warm habitat for rodents near the bulbs. In spring, as the ground begins to thaw, gradually remove the mulch layer to allow the soil to warm up and dry.
Lilies grown in containers require specific winter care due to their increased vulnerability to cold, as potted plants are more exposed to temperature fluctuations and their roots are less insulated than those in the ground. Moving containers to an unheated garage, shed, or a cool, frost-free location where temperatures stay between 35-45°F (2-7°C) is an effective strategy. If moving pots indoors is not feasible, insulating them outdoors with materials like bubble wrap or frost blankets offers some protection. Tilting outdoor pots can also help prevent water from accumulating and freezing around the bulbs. During winter dormancy, container lilies need minimal watering, just enough to prevent the soil from completely drying out, typically once a month.
In very harsh climates or for particularly tender varieties, lifting and storing bulbs indoors for winter is an effective option, done after the foliage has died back, usually after the first frost. Carefully dig up the bulbs, gently remove excess soil, and inspect them for any signs of disease or damage. Allow the bulbs to air dry for a few days in a cool, dark, and well-ventilated area. Once dry, store them in breathable containers like cardboard boxes or paper bags filled with peat moss, vermiculite, or sawdust, ensuring good air circulation and preventing direct contact between bulbs to inhibit mold growth. Store these containers in a cool, dark place with temperatures between 35-55°F (2-13°C) until spring planting.
Dealing with Cold Damage
Despite preventative measures, lilies can sometimes experience cold damage, which manifests in several recognizable ways. Common signs include wilting or drooping leaves, often accompanied by discoloration such as yellowing, browning, or the appearance of black or translucent patches. In severe cases, stems may become soft or mushy due to the freezing and rupturing of plant cells. New shoots emerging in spring might also appear blackened or stunted if damaged by late frosts.
Upon noticing these signs, assess the extent of the damage to determine the appropriate course of action. If only the tips or outer leaves are affected, the plant often has a chance of recovery. More extensive damage, such as widespread mushy stems or significant blackening, may indicate a more severe impact, potentially affecting the bulb’s long-term viability.
To aid recovery, remove any clearly damaged foliage or stems using clean, sharp pruning tools. New, healthy leaves often emerge quickly after superficial damage. Ensure the lily’s planting site continues to have good drainage, as excess moisture can exacerbate issues, and avoid overwatering during recovery. While the plant may appear stressed, the bulbs themselves are often resilient and can recover even if the initial growth is compromised, though they might lose some vigor. A light application of balanced fertilizer supports new growth.