To learn the secret of growing sunflowers to record-breaking sizes and heights, I turned to Dr. Tom Heaton, the worlds foremost sunflower breeder and Renees Garden sunflower seed supplier. Tom has been breeding sunflowers for 30 years and has changed the market by bringing a huge number of new shapes and colors to the seed business. His wholesale seed production company specializes in long-stemmed pollenless cultivars for the cut flower market and home garden. He has made different kinds that range from burgundy and ruby red to orange, peach, apricot, bright yellow, and fiery bicolors. Most of Renees Garden sunflower varieties are from his exuberant collection.
Tom has also been working on breeding the best tall competition varieties, such as “Giant Edible Sunzilla” and “Heirloom Titan,” which is good news for home gardeners who want to grow giant sunflowers. Tom keeps the longest stalk and biggest seed head of this variety in his garage every year so that he can compare them to the next year’s. He currently prizes a 17-foot stalk and a 24 in. a seed head! Tom has kindly agreed to write this article about how you can grow giants like these in your own garden.
With their bright cheerful faces reaching towards the sky sunflowers are a summertime icon. But can these sun-loving plants actually get too much sun? While sunflowers need at least 6 hours of direct sunlight per day, too much sun can cause problems if other factors like water and fertility aren’t addressed.
In this article, we’ll explore the ideal sun requirements for sunflowers and when too much sun can damage plants. Read on to learn expert tips for keeping your sunflowers happy even in the hottest, sunniest conditions.
Do Sunflowers Need Full Sun?
Sunflowers thrive best with lots of light When planning and caring for your sunflower patch or containers, keep these sun requirements in mind
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Sunflowers perform best with a minimum of 6 hours of direct, unfiltered sunlight per day. Full sun (at least 8 hours) is ideal.
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Morning sun is essential. Sunflowers open with the rising sun, so sun early in the day ensures proper development.
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In very hot climates, a bit of afternoon shade may be beneficial to prevent stress. But don’t shade for more than 2-3 hours.
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Sunflowers grow best when sunlight hits flowers and leaves from all directions, so plant in open areas.
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If sunlight is blocked, sunflowers will bend and twist as they compete for sunlight access.
So while they can tolerate partial shade, full sun is a must for the vigorous growth and massive flowers that make sunflowers shine.
What Happens if Sunflowers Get Too Much Sun?
While sunflowers love soaking up the sunshine, extreme heat and light levels can take their toll. Signs of sunflower stress from excessive sunlight include:
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Wilting or drooping leaves and flowers
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Brown or white patches on leaves, leaf scorching, or burnt leaf edges
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Stunted growth and smaller flowers
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Premature death or reduced lifespan
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Flower heads drying out or facing downward
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Increased vulnerability to pests, fungi and disease
Several factors play a role in how much sun is too much for sunflowers. The varieties you choose, soil moisture and nutrients, and climate conditions all impact how well equipped your plants are to handle intense sun.
Best Sunflower Varieties for Full Sun Conditions
Some sunflower types handle heat and sun better than others. These varieties tend to withstand too much sun well:
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Oilseed sunflowers – Types grown for oilseed production are bred to be resilient. ‘Peredovik’ and ‘Sunrich Orange’ are good choices.
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Large-headed single stem sunflowers – Giant single bloom varieties like ‘Mammoth’ tend to tolerate heat.
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Smaller flowered types – Miniature sunflowers with smaller bloom sizes cope better. Try ‘Elf’ or ‘Sunny Smile.’
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Heat-tolerant hybrids – Newer sunflowers bred for hot climates do well, including ‘Hot Sunsation’ and ‘Starburst.’
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Native sunflower species – Hardy wild types like Jerusalem artichoke handle higher heat.
Avoid sowing more delicate ornamental or thin-stemmed types during hot, dry weather. Choose sunflower varieties suited to your climate and light conditions.
Effects of Moisture and Nutrients on Sunflower Sun Tolerance
Sunflower plants that get adequate water and nutrition are better able to withstand intense sunlight than stressed plants.
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Soil moisture is crucial. Sunflowers need 1-2 inches of water per week from rain or irrigation. Deep watering is best to encourage deep roots.
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Grow sunflowers in nutrient-rich soil enhanced with compost. Fertilize lightly every 2-3 weeks if needed.
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Mulch around plants to retain soil moisture and reduce water needs.
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Monitor for signs of wilt and water immediately if leaves droop.
Healthy, hydrated plants with sufficient nutrients can bounce back from sun damage more easily than stressed plants.
Climate Conditions and Sunflowers
Hot, arid climates challenges sunflowers more than cooler regions. Here are some climate factors that impact sun tolerance:
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Temperature – Areas with extreme summer heat above 90°F stresses plants more than cooler climates.
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Humidity – Low humidity exacerbates leaf scorch and flower damage more than higher humidity.
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Wind exposure – Sunflowers in open, windy areas lose more moisture through leaves.
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Growing season – Where summers are very short, sunflowers need all the sun they can get.
Adjust your planting schedule and care routine based on your local climate and seasonal weather patterns.
Solutions for Sunflower Plants Getting Too Much Sun
If your sunflower leaves are wilting or blooms drying out from excess sun, here are some remedies to try:
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Add mulch around plants to cool roots and retain soil moisture.
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Install temporary shade if possible, such as shade cloth. Avoid shading for more than 3 hours maximum.
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Water thoroughly in early morning to allow plants to hydrate before the sun hits.
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Mist leaves with water to create a cooling effect and prevent wilting.
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Avoid applying nitrogen fertilizer during hot spells which can exacerbate drought stress.
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Plant heat-tolerant varieties selected for your growing region.
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If planting in containers, move pots to a shadier spot for a portion of the day.
Adjusting your care methods and choosing resilient varieties can help minimize sun damage. But the reality is sunflowers are made for full sun and small amounts of leaf scorch won’t severely reduce the harvest. Some slight cosmetic damage is worth the tradeoff for vibrant blooms and happy pollinators!
Maintaining a Balance of Sun and Shade
Sunflowers thrive on sunshine but can tip into stress when sunlight is at extremes. Here are some final tips for balancing their sun exposure:
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Stick to full sun locations but provide afternoon shade if possible in peak summer. Even reflected shade counts.
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Rely more on morning sun which is kindest to flowers. East or southeast exposure is ideal.
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Shade younger plants until established. Mature plants handle more sun than seedlings.
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Give adequate space between plants and use row covers to maximize airflow.
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Grow sunflowers under light shade from trees or vines rather than dense shade.
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Reduce water stress and nutrition issues to strengthen sun resilience.
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Select varieties suited for sun intensity in your climate zone.
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Closely monitor plants and adjust conditions at first signs of sun damage.
With smart variety selections, preventative care, and quick response to early symptoms, your sunflowers can thrive under even the most blazing summer sun!
Conclusion
While sunflowers need at least 6 hours of unfiltered sunlight per day, too much intense sun paired with other stresses can cause wilting, scorching, stunted growth or premature death. Steps like providing midday shade, misting leaves, mulching, and choosing heat-tolerant varieties can mitigate damage from sun overexposure. Maintain robust plants through proper watering, nutrition and care for the best sunflower success even in sweltering sunlight. By following the tips in this guide, your sunflower garden will stay vibrant through the sunniest summers!
Site and Soil Preparation Are Critical
Sunflowers do best with 6 to 8 hours of direct sunlight a day. The more sunlight they get, the bigger and better they will grow. Pick a spot that has good drainage, and get the soil ready by digging a circle about 2 to 3 feet around and 2 feet deep. Sunflowers need a lot of nutrients and can use up more soil than many other plants. This is especially true if you want them to grow very tall, so the soil needs to be replenished every season.
Work in a slow release granular fertilizer – one that also contains trace minerals – about 8 in. deep into your soil. Tom uses Osmocote, but I’m going to add a bucket full of rabbit manure that has been composted and a balanced slow-release granular fish fertilizer because I grow organic plants and rabbits. You might want to add something to your soil besides composted manure and an organic slow-release balanced fertilizer. This could be greensand or dried seaweed, which contain trace minerals.
Harvesting and Enjoying Giant Seed Heads
Protect the flower head with a mesh onion bag, a loose burlap or paper bag as the petals fall off, the center florets dry out, and the seed kernels start to swell in the disks. Carefully climb a stepladder and do this. This keeps birds from stealing your seeds, so the heads will be perfect when you’re ready to show them off to your friends or proudly stand them on their long stalks at the county fair. Cut the stalks at the base when the ripened seeds develop a hard shell. To keep them for your bird feeder, wait until the seeds are completely dry, then rub them over wire mesh into a basket or take them out by hand. Store in tightly closed containers to keep rodents away.
How Much Sunlight Does a Sunflower Need?
Why is my sunflower dying?
A dying sunflower is often because the sunflower is in too much shade or the soil is too damp. Sunflowers need at least 6 hours of sun and well-draining soil. Sunflowers droop and die back before flowering in too much shade. If the soil is too damp the sunflower’s leaves turn yellow with a wilting, dying appearance.
How much sun do sunflowers need?
So it’s best to protect seedlings with row covers or screening, removing the cover once the plants are 1 to 2 feet tall. For the best flowering and sturdiest stems, plant your sunflowers in full sun, meaning at least six hours of direct sunlight per day.
What happens if a sunflower gets too much sunlight?
Plants get their energy from sunlight. However, chlorophyll and carotenoid (the two photon-capturing molecules) will absorb more energy than needed if the plants get too much sunlight. This over-absorption leads to the generation of certain reactive species of oxygen, which will destroy your sunflowers.
Can You water sunflowers too much?
Too much of a good thing can turn into a bad thing. Many new gardeners who plant sunflowers will make the mistake of watering sunflowers too much. When you water these plants too much, it can lead to issues such as root rot. Root rot can most certainly kill your sunflowers and you will want to avoid having this happen at all costs.