Refer to the USDA's Plant Hardiness Zone Map (see Resources for link) to see which zone you live in. Zones are created based on the average lowest temperatures over a 15-year period. Plants recommended for your zone should be able to endure the coldest winter temperatures. Hardiness zones also project when the last frost will be.
Make notes of the growing conditions of your garden. How many hours of sunlight will the flowers get? Does the area have good drainage or sandy soil?
Call local nurseries and ask what types of everblooming flowers they carry for your hardiness zone. A number of flowers have everblooming varieties. Daylilies were developed to produce flowers that bloom and then bloom again from May until the first frost. Varieties of begonias, gardenias and geraniums are a few other types of everblooming flowers.
Purchase everblooming plants, seeds and bulbs that will thrive in your garden's growing conditions. Check that the combination of plants share similar soil and water needs. Choose plants of similar height and colors if you want your garden to look formal and uniform. Mix up the sizes, textures and colors to give your garden a more casual, creative look.
Dig up grass and weeds, and remove large rocks and root systems from your plot.
Use a soil testing kit to take the pH level. Organic fertilizer can supplement a lack of nutrients, but some flowers do not bloom as much when fertilized. Check your plant descriptions for nutrient needs, and mix native topsoil and garden compost into your soil. This will heighten the level of your garden so excess water runs off and will help the soil retain more nutrients and water.
Plant your flowers with the tallest plants in the back. Follow spacing and depth instructions included in the planting guidelines for each flower. This will allow for good air flow and sunlight in your garden, and enable the best possible health for each plant.
Cover your garden with a 1-inch layer of mulch. Pat the area around each stem.
Water your everblooming garden per the flowers' instructions.