Sunflowers aren't just the solitary flower you might think; each plant consists of 1000-2000 tiny flowers called disc and ray florets.
The plants belong to the Asteraceae family; their growth rate depends on the genetic background of the plant and the growing season environment.
The life cycle of the sunflower begins with planting a single seed and follows through germination, leaf, and plant development. Then follows young to adult plant and budding, before repeating the cycle when the pollinated seeds are harvested or left to fall naturally.
Sunflower growth has 2-primary stages, vegetative and reproductive (referred to as V and R respectively) then split into further subsections to help with identification:
Table of Contents
Sunflower Vegetative Stages
Sunflowers prefer to be planted directly into the soil as they don't respond well to having their long taproots disturbed.
They thrive in hot, sunny conditions, so plant them in a sheltered spot where they will receive at least 6-hours of sun daily.
The soil should be well-draining and loose to allow those roots to spread. They prefer loamy or sandy soil but are hardy (recommended in Hardiness Zones 2-11) and grow in most other types if treated with nutrient-rich fertilizer before planting.
Wait until the last spring frost has cleared before sowing any seeds. Plant them about 6” apart and 1-1.5” deep.
A tip for late-blooming flowers is to sow a few seeds each week; hence, promising a glorious display well into the fall.
2. Germination- 2-10 days
It takes 2-10 days for the tough shell of the seed to soften and crack. Simultaneously, a root grows downwards, and a shoot heads upwards to penetrate the soil's surface, searching for the sun.
It is called vegetative emergence (V1); the seedling takes about a week for the first leaf to appear.
3. Seedling – 10-35 days
As the stem grows taller, it also becomes thicker, and leaves start to grow. They're heart-shaped, to begin with, and usually form in pairs; It is known as vegetative state, and the number of healthy leaves longer than 4cm (true leaves) denotes its phase. For example, 4 leaves = V4, 9 leaves = V9.
Any leaves that have withered and died beneath the healthy ones leave 'scars' and are included in the count.
Sunflower Reproductive Stages
4. Growing a Bud – 35-65 days
Stages R1 – R4 cover the stages from the moment the first bud emerges until it is ready to flower.
Each seed produces a single terminal bud - R1; at this stage, it is a miniature flower head, not the cluster of leaves that it appears.
Viewed from above, it resembles a star with multiple points.
The bud elongates until it sits at around 2cm above the nearest leaf growing from the stem. This is stage R2, R3 occurs as the bud exceeds 2cm.
The sunflower needs plenty of sun and water at this point. It practices an extraordinary phenomenon called heliotropism; the bud follows the sun to capture as much energy to grow big and strong.
Stage R4 is when the flower head (inflorescence) begins to open, proudly displaying the multiple tiny flowers within.
5. Adult Flower – Day 65 – 85
Stage R6 is the blooming stage. The long, yellow petals gently unfurl, each a flower in its own right, called a ray floret. Each consists of clusters of tightly packed flowers known as disc florets, and here, the male and female reproductive organs are stored.
6. Pollination – Day 65 – 85
As the season progresses, more pollinators, including bees and butterflies, visit the disc florets in the brown center circle of the sunflower. They sip the nectar and roll in the pollen, transferring it from plant to plant, fertilizing as they go.
Most sunflower varieties can self-pollinate as they have both male and female reproductive organs; however, pollination by insects or on the wind is much less strenuous for the flowers.
7. Seed Development – Day 85 – 105
Once pollination is over, the back of the flower head turns pale yellow (R7). It is nature's way of telling us that the fertilized seeds are developing and ripening.
As the bracts – the small leaf-like structures found beneath the flower head – begin to fade to yellow and green, the sunflower is at full maturity.
The seeds will attract birds, animals, and insects, and the magnificence of the showy head remains to host them all.
It might bloom until day 125 before showing signs of wilting.
8. Harvesting – Day 105 - 125
If you have left it late, and the wildlife has already stripped the sunflower, remove the plant and add it to the compost.
If you catch it with the seeds still intact, it is time to harvest (R9).
Cut the stem at 4”-6” beneath the flower head and hold it over a large container.
Brush your hand across the seeds multiple times to release them into the bowl. Use a fork to free those more stubborn.
If you're using the yield for eating purposes, dry them out in the late autumn sun before storing them.
They make perfect wildlife food as they are; to keep for planting in next season, store them in an airtight container in a cool, dry place.
As the sunflower seeds ripen, some will fall into the ground beneath.
They remain dormant throughout the winter, only germinating when they feel the heat from the early-spring soil.
And so, the life-cycle and the sunflower growth stages begin again.
These are suggested timelines for the growth stages of a sunflower; they change by variety.
Not all sunflowers are giant plants; some are compact, suit container growth and barely surpass 1 ft. tall.
Other varieties include those with single or branching stems, those that produce lots of pollen, and those used in bouquets that produce little or none.
All sunflowers signify summer and a fascinating, eternal life cycle.