Knowing how much water sunflower plants need at different points in the growing process helps you keep your plants strong and healthy. Sunflowers (Helianthus spp.) are instantly recognizable with their oversized blooms and sunny yellow petals.
While sunflowers are tolerant of many conditions and are generally easy to grow, regular watering is important for flower development. They need lots of water when the plant first starts to grow but are slightly drought tolerant once established. Consistent watering is especially important just before and just after blooming.
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Germinating sunflower seeds need frequent, light watering to keep the soil consistently moist. Once sunflowers are established, they need about 1 inch of water every week between rain and irrigation.
Growing Conditions for Sunflower Plants
A sunflower's growing conditions can affect its watering needs and its overall health. Sunflowers need sunny growing conditions to thrive, but they also need soil that drains well. Heavy clay soil that doesn't drain well can cause rainwater and irrigation to pool, which can damage the sunflower's roots. You can amend the soil to help it better drain if your garden soil isn't ideal.
Water Needs for Starting Sunflowers
Water is especially important for germinating sunflower seeds. Keep the soil consistently moist, using frequent, light watering until the sunflower seeds germinate, which usually takes seven to 10 days. If you start your sunflower seeds indoors in seed-starting pots, you can cover them with clear plastic bags or plastic wrap to help keep the soil and seeds moist. Once planted in the ground, irrigate the seedlings consistently over the root zone of the growing sunflowers.
Water Needs for Established Sunflowers
Once established with a strong, deep root system, sunflowers are slightly resistant to drought. While they can't handle long periods of drought without showing signs of water stress, they can usually go several days to a week even in the heat of summer without being watered. Sunflowers generally grow well with 1 inch of water per week, whether from rain or supplemental irrigation.
The chances of water stress are more likely 20 days before and 20 days after sunflower plants bloom. Keeping the plants well watered during that period can improve the yield of your sunflowers. It also helps the roots stay strong, which is important as the blooms grow since the sunflower plants become top heavy.
When you water sunflowers to supplement rainfall, water them deeply to encourage deep root growth. Apply several gallons of water to the sunflowers once per week or when the top 2 inches of soil are dry for deep watering as needed, being careful not to waterlog the soil. An ideal goal is to give the sunflowers enough water to moisten the top 6 inches of soil. You might need to water more during especially dry periods. Skip your supplemental watering if you're receiving lots of rainfall.
Sunflowers in Pots
You can grow sunflowers in pots if you don't have the garden space for them. Water requirements are often higher for potted plants. The soil is limited and doesn't hold water the same way a garden bed does. Check the soil daily or every other day to see if it needs more water by pressing your finger into the soil and irrigating when the top 2 inches are dry. When you irrigate a potted sunflower, add water until it runs out of the drainage holes in the container.