Fill it with homegrown compost and soil. A raised bed will get annual flowers and vegetables through a light mid-summer frost. Cold frames also come in handy. A cold frame or cloche is really just a temporary greenhouse. A cold frame gives mountain gardeners an edge especially in the spring and the fall.
Container gardens can also be an advantage.
Bright pots of flowers can be moved inside if there is threatening weather. Warm season veggies like peppers or tomatoes can be put in a hot spot around the house to maximize a microclimate. New containers are decorative and can fit into any design scheme. Once the mud season is over, the real challenge is preventing gardens from becoming deer or elk salad. On non-edible plants, use Bobbex.