This is a question with many answers. In some ways you can plant right now.
Starting your garden indoors:
It is time to start some plants indoors. Those plants include tomatoes, peppers, and flowers like geraniums, petunias, begonias, and impatiens should be started.
Starting your garden outdoors:
Outdoors, if the ground has thawed and is not soppy wet you can plant dormant trees, shrubs, roses, berries and other hardy plants. Remember these should be DORMANT! If you buy a plant that has been inside and has broken dormancy there is a good chance of killing that plant before it gets a chance to get acclimated.
Look toward the mountains:
In the Spokane area there are two general ways to tell when to plant that people have used here for many years. For your cold season crops like Spinach, lettuce, carrots, radishes, onions and cabbage family plants you can plant when the snow melts off of Mica Peak in southeast Spokane County (usually about the first to middle of April). For your warm season crops, tomatoes, peppers, corn, melons, etc., wait until the snow melts off of Mount Spokane or after the average frost free date for Spokane of May 15th or better yet, especially for the melons, wait until the first of June.
A planting guide for many vegetables is available at www.nwseed.com or at either Northwest Seed & Pet location. Spokane's number one source for seeds.