How Much Sun & Water for Sunflowers?
A field of sunflowers (Helianthus annuus) blowing in a summer breeze can evoke a romantic road trip through the south of France or an idyllic impressionist painting. But how much sun and water do you need to grow sunflowers in your own garden? As their name implies, sunflowers require sunny conditions to thrive. They also need about an inch of water per week. Sunflowers come in many varieties, some of which are hardy as far north as U. S. Department of Agriculture plant hardiness zone 3.
Sunflowers need full sun, which means at least six hours of unfiltered sunlight every day. Sunflowers that get enough light produce abundant blooms that turn throughout the day so they are always facing the sun. Because they're such sunseekers, it's difficult to grow healthy sunflowers in a bright indoor location. If you decide to take the challenge, expect a lower yield of blooms.
Keep the soil around newly planted seeds evenly moist. Water seedlings every couple of days or more often if conditions are especially hot and dry. Mature sunflowers can adapt to drier conditions, as their expansive root systems seek out water underground. Planting sunflowers from seeds is the best way to encourage a healthy root system that ensures that your specimens get enough water for the entire growing season. However, you can supplement their water during very dry periods by giving the ground around the plants a deep soak. Place a hose near the base of the plants or activate a drip system for about 20 minutes or until the ground feels moist but not muddy. Do not spray the flowers themselves, as wet plants encourage disease.
Plant sunflower seeds after all danger of frost has passed. Choose a spot with fast-draining, somewhat alkaline soil where the flowers will receive full sunlight, and work in plenty of well-composted manure. Poke a hole in the growing medium at a depth of approximately twice the length of your seed, cover it with soil and pat the soil firmly to ensure good contact. Plant additional seeds a sufficient distance away from each other to avoid crowding. Typically, plants need 1 to 2 feet of space, but individual varieties have different space requirements, so check your seed packet. To prevent seeds from washing to the surface when you water them, outfit your hose with a misting attachment or use a watering can with a fine spray head. Garden netting can protect newly planted seeds from being poached by hungry birds or other pests.
Types of Plants
Sunflowers are available in a wide range of colors, sizes, bloom variations and cold hardiness. Some varieties, such as swamp sunflower (Helianthus angustifolius), USDA zones 6 through 9, are perennial. Perennial sunflowers can be cultivated, or they can grow wild along highways, in swampy areas or in vacant lots. Wild sunflowers are self-sufficient and don't need intervention to get enough sun and water. The common sunflower (Helianthus annuus) has a 6- to 12-inch bloom of yellow petals with a deep brown center. It can grow up to 12 feet tall, although it typically reaches a height of 4 to 5 feet. Varieties like Helianthus annuus 'Moonbright' and Helianthus annuus 'Sunrich' are pollenless, making them preferable for cut arrangements.
Sarah Lariviere's debut novel The Bad Kid (Simon & Schuster) is a 2017 Edgar Award finalist. She has taken college courses in landscape design and permaculture, and is an avid gardener.