Based on air temperature and light, Juneau has at least a four-month growing season, though that can be stretched by modifying the growing season. But cold soils mean slow growth for many crops.
The conventional wisdom is that the chance of killing frost is about gone by May 8th. Potatoes can go in before that and some seeds, but tender started plants are risk. Many gardeners plant most seeds outside by May 1, except for carrots and parsnips, which need more warmth to germinate, and can go in by the middle or end of May, depending on your location and spring weather conditions.
For a local example to provide inspiration and information, read the late Cliff Lobaugh’s “Monthly Calender” ( pp.174-176 Gardening in Southeast Alaska, 3rd ed. 2007). It describes his yearly sequence of eating from his Admiralty Island garden, including when he prepared beds, planted and harvested garden produce, harvested wild edibles, and prepared and stored produce. By April he would be harvesting both wild and cultivated greens.