Utah Planting Guide for Sunflowers

Temperatures

• Sunflower seeds germinate best in a temperature ranging between 46 and 50 degrees Fahrenheit. While frost won't harm the seeds initially, once the sunflowers have germinated, frost kills or stunts the plants. While microclimates vary depending on where you are in Utah -- and even where your garden is situated against your home -- the last frost date in much of the state ranges between mid-May and mid-June. If you're unsure of when your individual region experiences the last frost, contact the Utah State University Extension office in your county.

Soil Preparation

• Sunflowers benefit from loose, deeply tilled soil. Using a spade, break apart your sunflower soil bed to a depth of 10 inches. No matter where you are in Utah, the state's soil always benefits from the addition of rich, soil-improving organic material. This includes shredded leaves and lawn clippings, but most often is compost. Utah State University suggests adding an inch of compost and working it into the dirt. This feeds the future sunflower plants and also helps increase soil aeration and moisture retention -- helpful in Utah's often arid conditions.

Planting

• For optimal sunflower seed germination, bury each sunflower seed approximately 2 inches below the soil surface. Space each plant a foot apart. If you're growing more than one row of sunflower seeds -- some gardeners like to grow sunflowers in bulk in order to harvest their seeds -- space each row of plants 30 inches apart.

Watering

• Sunflower plants need deep, infrequent irrigation. Apply enough water to get the dirt wet to a depth of 6 inches. Then hold off on watering your Utahan flower bed until the soil has dried out to this depth. This encourages each sunflower plant to extend its roots far and wide -- in contrast, frequent and shallow irrigation promotes shallow, narrow root growth -- and makes them more resistant to the state's occasional drought seasons.