The expansive state of Alaska enjoys long summer days but also the reality of brutally cold winter weather. Summer highs are in the 60- to 75-degrees Fahrenheit range, while winter lows drop from -20 to colder at times. Gardeners in Anchorage, Fairbanks, Galena, Yukon, Juneau, Kodiak and Seward know that last frosts occur in May but the first frosts may happen in mid-September. If perennial plants do not have a chance to acclimate to cooler temps, or "harden off," they may not survive well.
Familiarize yourself with your landscape. Note which areas receive abundant sunshine during the growing season, and which tend to remain cooler and shaded. Also note the soil, giving favor to areas with moist but well-draining soil. Sandy soils with organic matter warm up more quickly in late spring, making them better suited for perennial gardens than heavy clay soils.
Choose perennials with a proven success for the climate and soils of Alaska. Consult your local cooperative extension office, which receives current information from horticulturists from the University of Alaska Fairbanks. Also visit local botanical gardens, talk with certified Master Gardeners, nurserymen and plant societies or garden clubs for recommendations for "fool-proof" perennials. Some popular selections include herbaceous peony; Asiatic, LA-hybrid, and Orienpet lilies; beebalm; and ligularia. According to the "Sunset Western Garden Book" and the University of Alaska Fairbanks, many popular perennials grown in the Lower 48 don't always do well in Alaska because of the untimely frosts that occur in September.
Amend the soil area where you wish to plant the perennials by adding compost or peat, and even some coarse sand to improve drainage. Till the soil to a depth of 12 to 18 inches before planting your perennial garden area. A well-prepared garden soil keeps plants healthy over the years.
Water perennials during the growing season as needed to supplement natural rainfall. According to recommendations by several Alaskan Master Gardeners, do not use water directly from the well or city water system since the water temperatures will be much too cold. Fill a large bin with water and allow the long summer days to warm the water first. Using water 60 degrees Fahrenheit or warmer avoids shocking or stunting the root growth of plants growing in a warm soil.
Divide large clumps of perennials that lose their flowering strength and overall vigor every 3 to 4 years. This is best done, in general, in August or early September after flowering wanes so roots have a chance to re-establish before days drastically shorten and temperatures cool in October.