How to Grow Zinnias If you're looking for a prolific annual flower for gardens and bouquets in a wide range of colors, try zinnias. The plants range from low growing, to tall and statuesque. Flowers come in all the colors of the rainbow depending on the variety. Group them in a flower or vegetable garden for color and to attract bees and butterflies When Where to Plant Zinnias Light: Zinnias grow and flower best in full sun. They can flower in part shade, especially in warmer climates with afternoon shade, but they may be more susceptible to disease and have fewer flowers. Soil: Zinnias grow best on fertile, well-drained soils high in organic matter. Well-drained soil is important because zinnia seedlings can be prone to rotting in cool, wet soils. Spacing: Plant zinnia seeds a few inches apart in rows or clumps. Thin to 8 to 18 inches apart, depending upon the variety, once the plant has grown four leaves. Planting: Plant zinnias in spring after all danger of frost has passed, around the same time you'd plant tomatoes. Zinnias are easy to grow directly-seeded into the garden. For sooner blooms, start seeds indoors 4 to 6 weeks before your last frost date. How to Grow Zinnias Throughout the Season Growth Habit: Zinnias come in a wide variety of plant sizes. Some are low-growing. 1-foot tall plants with a mounding habit. Others are 3-foot tall plants with big flowers. Plant the right variety for your usage and that your space allows. Mounding varieties have smaller flowers and produce more ornamental looking plants. Taller varieties are often used for cutting and are best grown in rows or clumps for a better visual effect. Staking: These flowers have sturdy stems, so do not need staking. Watering: Zinnias need moist soil to grow their best. This is especially true of young plants. Water deeply a few times a week so the soil stays moist 6 to 8 inches deep. Don't overwater because zinnias can also succumb to rot diseases especially on wet, clay soils. Once established, zinnias a relatively drought tolerant. Fertilizing: Amend the soil before planting zinnias with compost. When flowers start to form, side dress with an organic 5-5-5 fertilizer to get more and bigger blossoms. Mulching: Mulch zinnias once they are established with a 2 inch layer of straw or bark mulch. This will help preserve soil moisture and prevent weed growth. Trimming Pruning: Deadhead (trim) spent flowers regularly to promote more flowering and to keep the plant tidy. To create bushier plants on tall varieties, pinch the growth tip of the plant when young. This will stimulate more side branching, a shorter plant, and more flowers. However, it may delay flowering, especially in cool summer areas.