How Much Sun & Water for Sunflowers?

Sunlight

• Sunflowers grow best in full sunlight. The number of hours of sunlight per day varies with the latitude. Some Northern Plains sunflowers can receive 14 hours of daylight per day during the longest days of the summer. Various sunflower varieties grow to different heights ranging from 3 to 6 feet. Plant in a portion of the garden where they won't be shaded by taller plants. They can survive in dappled shade, but they'll grow slowly. The plants will not thrive and seeds may not develop on the heads of sunflowers grown in full shade.

Temperature Requirements

• Sunflower seeds require soil temperatures of at least 50 degrees Fahrenheit for germination. Soil warmth is commonly supplied by solar radiation with several days of sunny weather required to warm the soil to this point. Plant growth slows if cloudy or damp weather lowers air temperatures below 50 F for any length of time.

Moisture Requirements

• Growing sunflowers require an average of about 1 inch every week. This moisture can be natural rainfall or irrigation, although overhead sprinkling or spraying may damage the flower and seed heads. Watering once a week allows the deepest penetration of the moisture and benefits the roots the most. The amount of water necessary for the sunflower plant to thrive doubles in high temperature -- 95 F or higher -- or in relatively low-humidity conditions.

Drought Tolerance

• Taproots of the sunflower plant extend as much as 6 feet below the ground. This gives the plant access to water resources other than moisture provided by rain and irrigation during the current growing season. While this makes the sunflower plant tolerant to drought, the plant thrives best if its water needs are met consistently. This reduces stress on the sunflower and improves plant vigor and production.