Alstroemeria, commonly known as the Peruvian Lily or Lily of the Incas, is a beautiful, tuberous-rooted perennial that brings a vibrant splash of color to the summer garden. Originating from the mountainous regions of South America, this plant thrives in temperate climates but is generally considered a tender perennial outside of USDA Hardiness Zones 7 through 10. Gardeners in colder regions must provide specific winter care to protect the fleshy, delicate rhizomes from freezing temperatures and excessive moisture. Successfully overwintering these plants ensures they return with vigorous, abundant blooms in the subsequent growing season.
Preparing the Plants for Winter Dormancy
The transition to winter care should begin in the late autumn, typically when nighttime temperatures consistently drop below 40°F or before the first hard frost is expected. At this point, the plant’s natural growth cycle signals the onset of dormancy, a period of rest that allows the plant to conserve energy. This process is triggered by cooling soil temperatures and the reduction of daylight hours. To prepare the Alstroemeria, the most significant step is to restrict water, as wet conditions combined with cold are the primary cause of rhizome rot. Allowing the soil to dry out naturally initiates the necessary physiological changes that halt active growth. The foliage will begin to yellow and die back, which is a normal sign of the plant entering its dormant state. Instead of cutting the stems, which can create open wounds susceptible to disease, it is often best to let the foliage collapse naturally, or to remove only the yellowed, spent material in the spring.
Protecting Alstroemeria Left In-Ground
For established Alstroemeria clumps in zones that experience light to moderate freezing, providing a thick layer of insulation directly over the planting site is the most effective winter strategy. This protection shields the subterranean rhizomes from extreme temperature fluctuations and hard freezes. The insulating layer should be applied after the foliage has died back and the ground begins to cool, but before it fully freezes. Apply a deep, loose organic mulch, such as shredded leaves, straw, or pine needles, to a depth of four to six inches directly over the root zone. This dense blanket traps residual heat in the soil, preventing the rhizomes from experiencing prolonged exposure to temperatures below 20°F. Good drainage is paramount for in-ground plants, as the fleshy roots are highly prone to rot when left in cold, saturated soil. If the planting site is naturally heavy clay, ensure the area is mounded slightly to allow excess winter moisture to drain away from the crown.
Storing Potted Alstroemeria Indoors
Container-grown Alstroemeria requires a different approach since the roots are far more exposed to cold air and rapid temperature drops than those in the ground. The pots must be moved to a sheltered, frost-free location before the first anticipated frost, as the roots lack the insulating mass of garden soil. The ideal storage environment is a cool, dark, or low-light space, such as an unheated garage, cool basement, or a cold frame, where temperatures remain consistently between 35°F and 50°F. This temperature range is low enough to maintain dormancy but high enough to prevent freezing. During this indoor storage period, the plants require minimal to no water. A very light watering once a month is sufficient to prevent the tuberous roots from completely desiccating while avoiding the risk of fungal growth and rot.
Transitioning Back to Spring Growth
Once the threat of the last hard frost has passed and the daily temperatures begin to rise, the Alstroemeria can be prepared for its return to active growth. The timing for this transition is typically in early spring, once the ground has thawed completely. For in-ground plants, the heavy winter mulch layer should be gradually pulled back to allow the soil to warm up and new shoots to emerge. Potted plants should be moved from their dark storage location into an area with brighter, indirect light, such as a sunny window or a sheltered porch. This gradual reintroduction to light prevents sun-scald on the emerging foliage. As new green shoots begin to appear, resume a regular watering schedule, ensuring the soil is consistently moist but not waterlogged. At this stage, a balanced, slow-release granular fertilizer or a liquid feed can be applied to provide the necessary nutrients for the vigorous summer bloom cycle.