It's almost impossible to ripen tomatoes without a greenhouse on the Kenai Peninsula, but the right varieties ripen most summers in Fairbanks, more than 5 degrees farther north. Yet the frost-free season in the coastal cities of the Kenai Peninsula is longer than that of the Interior, and many perennials grow on the Kenai that cannot survive in Fairbanks. A lot depends on what you want to grow. Some plants, such as tomatoes and corn, require air temperatures well above freezing to grow, and need relatively warm soil as well. Even if the frost-free season is long enough for the life cycle of these plants, they will mature only if there is enough truly warm weather.
Corn even requires warm nights to mature properly.
Soil warmth is also influenced by the number of degree days above freezing. For annual plants, the main remaining climate requirements are enough sunshine and sufficient water. If the plants are watered artificially, most will do best with as much clear, sunny weather as possible. This is one of the reasons variety selection is so important in Alaska. Perennial plants have additional climatic needs.