Two factors affect the type of flowers that will grow in Minnesota. They are the climate and soil of the state. The USDA divides the Minnesota climate between USDA zones 2 and 4. In winter, northern Minnesota experiences temperature lows as cold as minus 45 degrees Fahrenheit. Minnesota soil is primarily made up of damp soils that contain rich glacial till. There is very little clay soil in Minnesota. Instead, there are abundant prairie and forest soils.
Dig up to 10 samples of soil from your yard or garden for soil testing. Remove one quart of soil from each location and mix the soil in a bucket. Allow the soil to dry and remove all debris, including plant roots, sticks and rocks. Collect one quart of soil in a sandwich bag and take it to your University of Minnesota county extension service. The county extension service agent will send your soil sample to the University of Minnesota Soil Testing Laboratory for soil analysis for a nominal fee. Test results will be returned to you within three weeks. Test results typically include soil composition, soil improvement and amendment recommendations, and pH.
Purchase soil amendments based on the recommendations in the soil test results. Soil amendments that will improve Minnesota soil include organic amendments to improve drainage, and nutrient content such as compost, peat moss and composted manure, as well as sulfur to lower pH and lime to raise pH.
Prepare your flower beds by breaking up the soil to a depth of 12 inches with a rototiller. Spread a 4-inch layer of soil amendments over the surface of the soil in quantities recommended by the soil testing results. Mix the amendments into the soil with your rototiller.
Select fast-growing, short-lived annuals and perennial flowers that are hardy to USDA zone 2 for Minnesota. Fast-growing annuals will complete an entire life cycle between the last and first annual yearly frost. Hardy perennials will withstand yearly winter temperatures. Some good examples of these flowers include peonies, Russian sage, foxglove, hostas, sweet pea and bachelor's button.
Open a planting pocket for transplants that is twice as wide as the root ball of the plants, but no deeper. Place the root ball of transplants into the soil and fill in around the root ball with soil. Create furrows or drill holes in the soil with a rake for your seeds. Plant each seed so that it is planted twice as deep as the width of the seed at its widest point. Cover the seed with soil. Water your plants and seeds so that the soil is as damp as a wrung-out sponge.
Check your plants weekly and water whenever the soil seems dry. The soil should remain as damp as a wrung-out sponge.