When Do Sunflowers Produce Seeds?


If you recently planted sunflowers in your yard, you may not have any seeds ready for harvest just yet.  In that case, you are probably wondering when sunflowers produce seeds, and if there is anything you can do to help them along.

So, when does a sunflower produce seeds?  A sunflower produces seeds that are ready for harvest 30 to 45 days after the flowers bloom, and 110 to 120 days after planting from seed.  Most sunflowers are annuals, meaning that they live only one year and must be replanted the following year.

Of course, depending on the variety of sunflower you choose, you may get fewer seeds or smaller flowers.  Other factors such as crowded spacing, over fertilization, and environmental conditions can all affect the quality (for example, oil and protein content) of sunflower seeds.

Let’s take a closer look at sunflowers, when they produce seeds, and the factors that can affect your harvest.

When Do Sunflowers Produce Seeds?

Sunflower seeds generally produce seeds that are ready for harvest between 30 and 45 days after they bloom.  The time from planting a seed to harvest mature seeds is 110 to 120 days.

Sunflower seeds will usually be ready for harvest by 110 to 120 days after planting seeds.

According to Purdue, sunflowers in temperate regions may mature in as little as 109 days

On the other hand, North Dakota State University suggests that the time from planting to maturity is closer to 119 days.

According to the University of Tennessee Extension,

“Sunflower seeds are generally physiologically mature when the back of the flower head is yellow. When the head turns brown on the back, seeds are usually ready for harvest.”

University of Tennessee Extension, https://extension.tennessee.edu/publications/Documents/SP721.pdf

So, you should plan on waiting about 3 months for the flowers to bloom, and another month after that for the sunflower seeds to be ready for harvest and eating.

How Many Seeds Does A Sunflower Produce?

A single sunflower can produce hundreds or thousands of seeds, depending on the size of the plant.

sunflower
Depending on the size of the flower, a sunflower can produce hundreds or thousands of seeds.

Some smaller varieties, such as “Teddy Bear”, only grow 2 to 3 feet (0.6 to 0.9 meters) tall, with flowers that have a 5-inch (12.7 centimeter) diameter.

Larger varieties, such as “Pike’s Peak”, can grow up to 15 feet (4.6 meters) tall, with flowers that have a 14-inch (35.6 centimeter) diameter.

How Long Do Sunflowers Live?

Most sunflowers are annuals, meaning that they only live one growing season.  You will need to replant sunflowers every year that you want to grow them.

sunflower
Most sunflowers are annuals, meaning they only live for one season, and need to be replanted every year.

At about 84 days after planting, the flowering on a sunflower plant will be complete.  By 119 days after planting (35 days later), the back of the head of the flower will be brown, and the seeds will be ready for harvest.

What Kind Of Sunflowers Should I Plant?

When selecting a sunflower to plant, make sure to choose one that you can grow in your climate!  For more information, check out the USDA Zone Hardiness Map to see what zone you are in.

Here are some sunflower varieties that you might want to try:

  • Rudbeckia Indian Summer Sunflower – this sunflower plant produces gold and yellow flowers that bloom for 12 weeks.  The plant reaches a height of 36 to 42 inches, with a spread of 12 to 16 inches.  In mild climates, you can sow seeds any time during the year.  For more information, check out Rudbeckia Indian Summer Sunflowers on the Burpee website.
  • Pike’s Peak Sunflower – this giant sunflower plant produces gold, orange, and yellow flowers that bloom for 6 weeks.  The plant reaches an astounding height of 12 to 15 feet, with a spread of 26 to 30 inches.  The seeds can be as long as 1.5 inches each.  For more information, check out Pike’s Peak Sunflowers on the Burpee website.
  • Kong Hybrid Sunflower – this giant sunflower plant produces gold and yellow flowers that bloom for 6 weeks.  The plant reaches a height of up to 13 feet, with a spread of 36 to 40 inches.  For more information, check out Kong Hybrid Sunflowers on the Burpee website.
  • Teddy Bear Sunflower – this dwarf sunflower plant produces gold, green, and yellow flowers that bloom for 5 weeks.  The plant reaches a height of 24 to 36 inches, with a spread of 14 to 16 inches.  For more information, check out Teddy Bear Sunflowers on the Burpee website.
  • Del Sol Hybrid Sunflower – this sunflower plant produces brown and yellow flowers that bloom for 6 weeks.  The plant reaches a height of 5 to 6 feet, with a spread of 8 to 12 inches.  For more information, check out Del Sol Hybrid Sunflowers on the Burpee website.
  • Mammoth Russian Sunflower – this large sunflower plant produces yellow flowers that bloom for 5 weeks.  The plant reaches a height of 9 to 12 feet, with a spread of 36 to 40 inches.  For more information, check out Mammoth Russian Sunflowers on the Burpee website.

Remember: although sunflowers can be transplanted, they are sensitive to transplant shock.  It is recommended to sow sunflower seeds directly into the soil where they will be grown.

Do You Need Two Sunflowers To Get Seeds?

No, you do not need two sunflowers to get seeds from the plants.  However, there is some evidence that pollen movement between plants (thanks to bees) can improve sunflower seed yield.

sunflower
You do not need two sunflowers to get seeds from the plant, but evidence suggests that yield can increase with bees to help carry pollen between two or more sunflowers.

Here is an interesting fact about sunflowers: a sunflower is not really one flower, but rather, 1000 or more tiny flowers growing together.

According to Purdue University,

“The sunflower head is not a single flower (as the name implies) but is made up of 1,000 to 2,000 individual flowers joined at a common receptacle. The flowers around the circumference are ligulate ray flowers without stamens or pistils; the remaining flowers are perfect flowers (with stamens and pistils). Anthesis (pollen shedding) begins at the periphery and proceeds to the center of the head. Since many sunflower varieties have a degree of self-incompatibility, pollen movement between plants by insects is important, and bee colonies have generally increased yields.”

Purdue University, https://hort.purdue.edu/newcrop/afcm/sunflower.html

What Other Factors Can Affect Growth Of Sunflowers?

The quality of care that you give your sunflowers  will help to decide how many flowers (and seeds) you get each year.  Remember that sunflowers need full sun (8 or more hours or sunlight per day).

Other important factors for sunflowers are temperature, watering, fertilizing, and spacing.

Temperature for Sunflowers

In order to germinate properly, soil temperatures for sunflower seeds should be at least 50 degrees Fahrenheit (10 degrees Celsius) and at most 91 degrees Fahrenheit (33 degrees Celsius).

The ideal soil temperature for sunflower seed germination is 70 to 78 degrees Fahrenheit (21 to 26 degrees Celsius).

At these temperatures, sunflower seeds should germinate in 4 to 11 days.  For more information, check out my article on sunflower seed germination.

According to the Old Farmer’s Almanac, sunflower seeds should be sown in the soil outside only after the last spring frost has passed.

You can find your last spring frost date on the Old Farmer’s Almanac website.

Watering For Sunflowers

Sunflowers are naturally resistant to both drought and heat, so you may only need to water deeply once per week, to encourage a strong and extensive root system.

garden hose
Water your sunflowers deeply and infrequently, to encourage strong and extensive root systems.

It will be difficult to under water them unless you really neglect your garden during a heat wave, or have very dry soil.

If you have a problem with dry soil, check out my article on dry soil.

On the other hand, over watering can spell death for your sunflowers, due to root rot or fungal diseases.  For more information, check out my article on over watering.

Fertilizing For Sunflowers

Before you plant a sunflower, add some compost to your soil.  It will provide organic material and nutrients for your sunflower as it grows.  The best part is that you can make compost yourself from ordinary yard and kitchen waste!

compost bin
Compost is a great way to provide nutrients and organic material to your soil, while recycling kitchen scraps and yard waste.

For more information, check out my article on how to make your own compost.

It may be necessary to use fertilizers as a supplement to compost, in order to provide extra nutrients if your soil is lacking. The best way to tell if you need fertilizer is with a soil test.

For more information, check out my article on soil testing.

A soil test will also indicate the pH of your soil.  The ideal pH range for sunflowers is between 6.0 (slightly acidic) and 7.5 (slightly basic).

If your soil pH is too low (acidic), you can add lime (calcium carbonate) to raise it.

If your soil pH is too high (basic), you can add sulfur to lower it.

Spacing for Sunflowers

Sunflower seeds should be planted at most 1 inch (2.5 centimeters) deep, with about 6 inches (15 centimeters) between each seed in the row.  The rows themselves should be about 30 inches (76 centimeters) apart to leave room for watering, weeding, and harvesting later in the season.

Support for Sunflowers

Some giant varieties of sunflowers can grow to 12 feet tall or higher.  As such, you may need to provide some support to keep them from falling over due to their own weight.

There are lots of ways to do this, including tying the sunflowers to a stake or trellis as they grow.  For more information, check out my article on supporting plants, and my article on trellises.

Conclusion

By now, you have a good idea of when sunflowers will produce seeds.  You also know a bit more about how to take care of sunflowers and how to avoid the problems that can affect your harvest.

I hope you found this article helpful – if so, please share it with someone who can use the information.  If you have any questions to ask or advice to share about sunflowers, please leave a comment below.

jonathon.david.madore

Hi, I'm Jonathon. I’m the gardening guy (not guru!) who is encouraging everyone to spend more time in the garden. I try to help solve common gardening problems so that you can get the best harvest every year!

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