Plant both annual and perennial flowers in spring when you wake your roses up. Wait until after the last frost lifts to give both roses and new flowers a warm-weather start.
Mix 3 inches of organic compost into the soil throughout the bed to strengthen existing roses and prepare the soil for new plantings. Use a hand fork to turn the compost into the top 6 inches of the bed, and then broadcast bone meal or 5-10-5 fertilizer throughout. Turn the fertilizer into the top 3 inches of soil.
Plant annuals such as impatiens, daisies, cosmos, verbenas, miniature fuchsias and pansies, or perennials such as asters, tulips, daffodils, dahlias and columbine. These flowers can grow in the partial shade of the roses. Plant nasturtiums, marigolds and mums to keep aphids and caterpillars away from the roses.
Water the garden with 2 to 4 inches of water to settle the plantings, and then switch to plant-specific watering schedules. Lay 2 inches of mulch across the soil to keep it moist and warm for all the plants and to prevent weed growth.