Sunflower Growth Stages

Sunflowers (Helianthus annuus) are the first plant many children ever grow from seed. For some of us, a single sprouting sunflower seed ignites a lifelong love of gardening (I know that was the case for me). 

Finding a summertime garden with a few towering sunflowers is not hard. You can also find fields filled with yellow blossoms in many parts of the world. Sunflowers are a significant global crop, grown for their edible seeds but, more importantly, for their oil.

This article explores the various sunflower growth stages you’ll encounter after planting a few of your own. 

How to Grow Sunflowers

Sunflowers are annual plants that complete a full life cycle in a single calendar year. Seeds are commonly planted in the spring when soil temperatures are above 55°F. The plants then bloom and produce seeds within the same summer and fall.

As the name implies, sunflowers thrive with lots of light. These flowers prefer at least 6 to 8 hours of direct sunlight daily. The flowers famously ‘follow’ the sun through the sky, slowly changing direction as the day gets later and later.

Provide rich, well-draining soil to ensure a healthy sunflower harvest. According to the University of Minnesota, sunflowers are incredibly responsive to nitrogen within the earth. For the average home gardener, however, it’s usually enough to apply a balanced source of fertilizer early in the growing season.

Sunflowers will grow with an average of 1 inch of water per week. Supplementary irrigation is rarely necessary except in times of severe drought. With that said, sunflowers naturally need more water when first germinating and sprouting.

Due to their sheer height, many sunflowers benefit from additional support. One way to get around this is by planting sunflowers in dense clusters that more or less support themselves. You can also use sturdy stakes or even a trellis to give your sunflowers a helping hand!

Sunflower Growth Rate

Sunflower varieties that can grow 6 feet or taller have no time to waste in terms of putting on height! Growth rates early in the sunflower life cycle can reach up to 10 inches per week, though average growth is much more conservative. 

Adjusted for all segments of the sunflower life cycle and differences in mature size, the average growth rate is about 2.5 inches per week.

Growth Stages of a Sunflower

Growing sunflowers is so simple that even a small child can do it! These garden beasts grow so quickly that it sometimes feels like you blink and it’s over, but a lot goes into transforming a sunflower seed into a towering behemoth.

On average, sunflowers mature from seed in 85 to 95 days. Smaller varieties can mature and begin flowering in as little as 60 days.

Whether you’re growing sunflowers for the nutritious seeds or simply for their ornamental value, the info below will teach you everything there is to know about this show-stopping flower and its inner biology.

1. Seed Germination

What we think of as the sunflower seed is a dry fruit. The actual seed (the part we eat) is contained within the thin shell (the part we usually spit out).

Seed Germination

There’s no need to remove the shell of a sunflower seed before planting. The seed can manage independently and will know the perfect time to crack open the shell from the inside to start sprouting. However, some growers prefer to score the shell to speed up germination.

Germination begins as the seed absorbs water through the outer coating. This absorbed moisture triggers cell division in the seed, which eventually causes the shell to split open as the seed expands. 

In optimal conditions, sunflower seeds should germinate within eight days.

2. Sprouting

Once the outer hull splits open, the sunflower seed’s first roots will emerge. The seed produces a young shoot topped with two embryonic leaves called cotyledons.

Cotyledons are primitive leaves that supply the seedling with energy during its first days of growth. Since the sunflower seedling doesn’t have any mature foliage at this point, it’s unable to photosynthesize and produce its energy. The cotyledons fill the gap while the seedling develops and finds its footing.

On average, it takes a few more days for the sunflower’s first ‘true’ leaves to start growing from the center of the cotyledons. As the seedling and its adult leaves get bigger, the cotyledons will likely fade and drop off. The young sunflower is now able to sustain itself using photosynthesis.

3. Vegetative Growth

The next 45 to 60 days, the sunflower will focus entirely on getting taller and stronger. New leaves will continue emerging from the top of the shoot. At the same time, the root system is expanding beneath the soil’s surface to provide critical stability and access to key resources like nutrients and water.

Most sunflowers produce a single stalk topped with a single flower bud. However, some specimens boast a branching growth habit with several individual flowers.

4. Bud Formation

The primary vegetative growth stage ends with the appearance of a small flower bud at the top of the stalk. It takes about 30 days for the bud to develop and open into the trademark yellow flower fully. Damage or stress to the plant during this phase can later interfere with the flowering stage.

Bud Formation

5. Flowering

A single sunflower can bloom for up to 20 days in ideal conditions. Each flower is a collection of thousands of florets called an inflorescence.

Sunflower inflorescences contain both disk and ray florets. The disk florets make up the dark center of a sunflower, where the seeds will eventually develop. The ray florets are the bright yellow petals that surround the disk florets.

sunflower Flowering

6. Pollination

Most sunflowers naturally self-pollinate. However, some hybrid varieties are self-sterile and require the transfer of pollen from a male plant to a female plant. 

It’s the disk florets that must be pollinated to form seeds. Ray florets are sterile regardless of the type of sunflower being grown.

Sunflowers may be pollinated by the wind or by flying insects. Bees are the primary pollinators of sunflowers, followed by other insects like butterflies and moths.

7. Seed Development

Sunflower seeds typically form and mature from the outside of the flower, moving inward. The seeds appear white initially but will darken to black as they ripen. This process can take an additional 30 days following pollination.

When to Harvest Sunflower Seeds

Wait to harvest your sunflower seeds until the remaining flower petals dry up and fall off the plant. The heads will start to droop when the seeds are near maturity. You can also check the back of the flower head — it should be yellow or brown rather than green, before cutting off the head to dry.

For more articles about plant growth cycles, here’s a link to Eggplant Growth Stages.

FAQs Sunflower Growth Stages

How long does it take a sunflower to grow?

Most sunflowers mature 85 to 95 days after planting. However, factors like the type of sunflower being grown and environmental conditions can mean that sunflowers mature anywhere from 70 to 100 days after sowing seeds.

Citations

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.