How to Grow and Harvest Sunflowers

By Bethany Hayes

Sunflowers are iconic and bring happiness to everyone who sees them. It’s hard to look at a row of sunflowers and not simple – they’re gorgeous. If you love them as much as I do, you might want to learn how to grow and harvest sunflowers in your garden. 

Did you know that sunflowers come in different colors and sizes? You can grow small sunflowers or ones that weigh up to 5lbs each head! Sunflowers come in yellow, red, orange, brown, and maroon, but the most common color is bright yellow with a brown center filled with seeds. 

Want to see these cheerful flowers in your garden? Keep reading to learn all about how to grow and harvest sunflowers. 

How to Grow Sunflowers in Your Garden

Sunflowers are far from complicated to grow. In fact, they’re one of the least picky flowers you could add in your garden, so they’re perfect for new gardeners. Here’s how to start growing sunflowers. 

Know When to Plant Sunflowers

Since you sow sunflower seeds directly into your garden, it’s best to wait until the danger of frost has passed. The soil should be around 50℉ or warmer when you plant your seeds. 

Depending on where you live, this means you should plant your seeds between the end of April to the beginning of June. Mother Nature plays a huge role, and even if the danger of frost is gone, the soil might not be warm enough based on the current temperatures. Always pay attention to the forecast. 

If you find that your soil still isn’t warming, but you’re ready to get planting, you can use black landscaping fabric or plastic. Lay it over the ground where you plan to sow the seeds and let it sit there for several days, soaking up the sunlight and warming the soil. 

Where to Plant Sunflowers in the Garden

Sunflowers love sunny locations – you might have guessed that based on their name. It’s best to grow them in areas that receive direct sunlight, typically 6-8 hours per day. Long, hot, sunny summer days are ideal for beautiful sunflowers. 

You also want a location that has well-draining soil that won’t cause it to pool up or create large puddles. Also, if possible, look for a place that might have shelter from strong winds. An example would be near a building or along a fence line. This is ideal because large varieties can become top-heavy; some of my tops weighed over 5lbs each! 

How to Prepare the Soil for Sunflowers

Sunflowers aren’t too picky about their soil, but they highly dislike compacted ground. Their long tap roots need to stretch out and breathe, so if you want to prepare your garden bed appropriately, make sure you dig down deep into the ground. 

The soil pH doesn’t matter either, but they do better in slightly acidic soil to be somewhat alkaline. The ideal range is between 6.0 and 7.5. What matters the most is that the soil is nutrient-rich and full of organic matter or composted manure because sunflowers are heavy feeders. 

You should either add plenty of compost or slow-release granular fertilizer in your soil. Be sure to mix 6-8 inches down into the ground so your roots can access the nutrients. 

Planting Sunflowers

It’s finally time to plant your sunflowers! Here is what you should know, but trust me, it’s easy as pie.

• The seeds should be planted 1-1.5 inches deep into the soil, and make sure to space the seeds around 6 inches apart. For larger varieties, you might want to space the seeds 10-12 inches apart. Another option is to plant as you want and thin later as they sprout and start to grow. 
• If you’re doing more than one row, space the rows about 30 inches apart, but if you do plant smaller ones, you can reduce that spacing. 
• To encourage healthy root growth and development, mix some fertilizer into the soil. It will help protect the flowers from strong winds; you want rock-solid roots. 
• You don’t have to plant sunflowers all at one time. You might want to stagger the planting, so they all bloom at different times. 

How to Care for Sunflowers

I love to grow sunflowers because they’re so easy to care for each year. They don’t require an intense watering schedule, nor do you have to fertilize all the time. Here’s how you can take care of these flowers. 

How Much to Water Sunflowers 

Your sunflower plants’ watering needs differ based on their current size. A small sunflower plant needs to be watered around the plant’s base often to help encourage deep root growth. You want a well-established plant.

Once your plant is established and starts to grow, water deeply but infrequently. Unless you have exceptionally dry weather, aim to only water once per week but often several gallons of water at that time. Remember, they have deep taproots, so you need to get the water down there. 

Do I Need to Fertilize Sunflowers?

Yes, sunflowers need to be fertilized, but you don’t need to do so often or a lot. The plants should be fed sparingly because overfertilization can cause the stems to break in half or fall over. 

When you fertilize the plants, dilute the fertilizer in water, and keep it away from the plant’s base. You should fertilize about 12-18 inches away from the stem. 

You Might Need Support 

Some, but not all, sunflowers need support. Even if you’re growing a tall cultivar, it doesn’t mean you need to provide support. If you end up needing to support the plants, bamboo stakes are a good choice.

Harvesting and Storing Sunflowers

Most sunflower varieties take around 85 to 95 days to mature, but some larger ones can take over 100 days. It truly depends on the cultivar you grow, so make sure you take a look at the seed packet and remember those days to maturity are based on your plants growing in ideal conditions. 

Gardeners become intimidated when it comes time to harvest their sunflowers. Despite your worries, it’s not nearly as hard as you might think, so let’s go over the steps to help you prepare. 

1. Wait until the flower starts to dry, either on or off of the stem, and the head begins to turn brown as the foliage turns yellow and the petals die. You’ll notice that the seeds are plump and loose.
2. You’ll need either sharp scissors, a garden knife, or pruners (depending on the size of the stems) to cut the head off of the sunflower stem. Try to cut 6-8 inches below the head. 
3. Now, you first need to brush off the flowers that are left on the head. You can rub your hand over the sunflower head, and they’ll come right off, leaving the seeds visible underneath. This is fun for kids to try!
4. Then, it’s time to remove the seeds. I find that bending the heads, especially the larger ones, tend to help loosen them up. Then, it’s trial and error to find what works best to remove the seeds. Sometimes, rubbing them a bit more forcefully with your hand will remove them. Other times, rubbing the heads against an object can force them off.

Another option is to leave the heads on the stems and wrap them with cheesecloth to let them fully dry on the stem. You also can cut the flower early and hang them upside down until the seeds are dry. 

Once harvested, you should rinse off the sunflower seeds and let them dry overnight. If you want to save them for replanting, keep them in an airtight container in a cool place or a seed envelope until the following year. 

Common Pests & Diseases That Bother Sunflowers

Two of the biggest problems you’ll face while growing sunflowers are the birds and squirrels – they love sunflower seeds! You might need barrier devices to keep birds away, and you can cover mature helps with garden fleece. 

Most sunflowers are insect-free and rarely bothered by pests, making it that much easier to grow these lovely flowers. They deal with some diseases, so let’s take a look at what you need to know about diseases and sunflowers. 

Downy Mildew

This is a fungal disease that causes mottling and pale areas on the leaf surfaces. It also can cause mold growth on the undersides of the sunflower heads and the leaves. Downy mildew causes the leaves to wither and die, infecting the oldest leaves first. 

It’s most common when you have cool, damp nights and warm, humid days. Downy mildew spreads by its tiny spores that can be carried by the wild, soil, or garden tools. Typically, it won’t kill a mature plant, but it won’t look so pretty anymore. 

Rust

Here’s another fungal infection that might bother your sunflowers. Rust will appear on the upper leaf surfaces, appearing first as yellow or white spots that eventually turn brown or black. Then, puffy blisters will appear on the undersides of the leaves. 

Over time, rust might spread to the stems and flowers, causing distorted or stunted growth. It’s most often spread from weeds that are in your garden already. 

If you spot it early enough, you can treat rust with a general garden fungicide, but if you have seriously infected plants, you’ll need to remove and destroy the plant. It’s quite disappointing, but it is better than the fungi spreading to all of the other sunflowers in your garden! 

Grey Sunflower Moth

The only pest you might need to worry about would be the gray sunflower moth. They like to lay their eggs in the developing blossoms. You might find greenish-yellow larvae with brown stripes down their backs.

Grey sunflower moths will destroy the seeds and feed on the flowers. Always pick off the worms if you see them and kill them. You can also try spraying your infected plants with Bacillus thuringiensis (BT) when you see the larvae. 

Start Growing Sunflowers This Year!

Don’t be intimidated. If you can grow green beans or tomato plants, there’s no reason why you can’t learn how to grow and harvest sunflowers in your garden. Not only do they look fantastic in your garden, but the seeds taste great. Give them a try this year – you won’t regret it! 

Learn more about growing and harvesting sunflowers

• https://extension.uga.edu/publications/detail.html?number=C1121&title=Growing%20Sunflowers%20in%20the%20Home%20Garden
• https://extension.umn.edu/flowers/sunflowers