The Alstroemeria, commonly known as the Peruvian Lily, is a popular herbaceous perennial recognized for its long vase life and vibrant, lily-like blooms. It is valued in gardens for its continuous flowering period, often extending from early summer into autumn. The optimal planting time for this tuberous perennial depends mainly on the form of the plant material—bare roots or seeds—and the specific climate of the planting location.
Optimal Timing for Bare Root Planting
Planting Alstroemeria as bare roots or potted nursery plants is the most common and fastest way to establish them in the garden. The two primary planting windows are early spring and early autumn. Spring planting should occur after the last hard frost has passed, ensuring the tender new growth is not damaged by freezing temperatures. This timing allows the roots to establish fully during the growing season before winter.
Bare roots should be set in the ground in spring when the soil is workable and starting to warm up. The ideal time is when daily temperatures do not exceed approximately 68°F (20°C). Fall planting is an option, particularly in regions with milder winters, and should be done several weeks before the first hard frost to allow root development. In either season, the soil must be well-draining, as the fleshy roots are prone to rot in soggy conditions.
Adjusting Planting Time for Climate and Hardiness Zones
The decision of when to plant Alstroemeria is influenced by your USDA Plant Hardiness Zone, which dictates whether the plant will survive the winter as a perennial. In warmer regions (Zones 8 through 10), Alstroemeria is reliably perennial and can be planted in either spring or fall. Fall planting in these zones allows the plant to develop a strong root system over the mild winter, leading to robust spring growth.
Gardeners in colder regions, generally Zones 5 through 7, must treat the plant differently. Here, Alstroemeria is often grown as an annual, or the roots are heavily mulched or lifted for winter storage. For perennial success in Zone 7, planting in the spring after the last frost is recommended. This gives the plants maximum time to establish before a protective layer of mulch is applied in the fall.
Planting Alstroemeria from Seed
Starting Alstroemeria from seed requires cold stratification due to the seeds’ natural dormancy mechanism. To encourage germination, the seeds must undergo this period, which mimics natural winter conditions. This process typically involves placing the seeds in a moist medium in a refrigerator for three to four weeks.
The best time to begin this process is in late winter or very early spring, about 8 to 12 weeks before the last expected frost. After the cold period, the seeds are moved to a warm environment, around 70°F (21°C), to stimulate germination. Once the seedlings develop their first true leaves, they can be grown indoors under bright light until all danger of frost has passed. Plants started from seed often take two to three years to reach maturity and produce their first blooms.