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Growing Sunflowers: Cheerful Gigantic Blooms

Helianthus annuus is a playful addition to the garden.  Growing sunflowers can reach over 12 feet tall and add to the biodiversity of your garden by bringing in pollinators and wildlife. I love to plant sunflowers in my garden – it is low maintenance and you can reap the benefits of giant bright yellow flowers! 

Historically, sunflowers have been cultivated for many generations by indigenous peoples.  Since then, hybridization has generated a wide variety of sunflowers that range in size, shape, and colors. Some cultivars are small, just a foot tall, while mammoth varieties grow up to 15 feet tall!  Not only does this adorable flower look like the sun, but it tracks the sun with the subtle movement of the flower head!  

This flower inspires many as a symbol of hope, radiance, and light.  To quote from Helen Keller, “Keep your face to the sunshine and you cannot see the shadows.  It’s what the sunflowers do.”  So let’s explore how to grow sunflowers in your garden!

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Quick Care Guide

Growing sunflowers
These growing sunflowers are giant showstoppers. Source: Dovima-2010
Common Name(s)Common sunflower, Kansas sunflower, mirasol, comb flower, golden flower of Peru, St. Bartholomew’s star
Scientific NameHelianthus annuus
Days to Harvest68-180 days
LightFull sun, 6-8 hours of sunlight
Water:Low to average, drought-tolerant past seedling stage
SoilRich well-drained loam sandy soils but grows well in poor disturbed soils.
FertilizerLow need, apply when planting seeds and during the seedling stage
PestsGray sunflower moth, cutworm, leaf miners, aphids, and birds
DiseasesPowdery mildew, rust, and other fungal leaf spots

All About Sunflowers

Sunflower closeup
Variegated sunflowers can have multicolored petals, as seen on this closeup. Source: foxtail_1

The common sunflower, Helianthus annuus, is the state flower of Kansas.  It is also known as the Golden Flower of Peru, or St. Bartholomew’s Star.  This flower is a genuine native of North America and easily grows throughout Canada, the United States, and northern Mexico. 

Let’s explore the parts of this beautiful plant.  The stem is sturdy with broad heart-shaped leaves.  They are covered in small coarse hairs.  The flowers range from 3 inches to 12 inches in diameter.  The center of the flower head is a rich chocolate color that is surrounded by golden yellow petals. In the head, you will find mini flowers or florets.  Each of these florets will mature into scrumptious sunflower seeds.  They contain an outer husk which you will need to crack open to find the nutritious kernel. 

The lifecycle of the sunflower from seed to harvest averages 125 days.  Once you plant the seeds, germination begins. A seedling will emerge within 10-15 days and the next stage of growth will be focused on stem and leaf development.  A month after planting, the sunflower will begin to focus its growth on bud development. Bloom time will begin in the summer, about 2 months after planting. The flowers focus on pollination which will encourage seed production. By the third month, you should see seed heads emerging. By early fall, the yellow petals will fade, indicating that the sunflower seeds are ripe and ready for harvest.  

The sunflower seeds are highly valued for culinary purposes. The seeds can be eaten raw or roasted, extracted for cooking oil or even used as a coffee substitute. The sunflower leaves have been used in salads, can be cooked or baked. The petals are edible and colorful garnish to your dish.  You can even cook the whole flower heads and eat it!  A personal favorite is the sunflower sprouts, these will be ready 2 weeks after planting the seed. 

Beyond edible purposes, the sunflower can be extracted for yellow, purple, and black dyes.  The stalks are used as fuel and can feed livestock. Or you can enjoy the cut flower in a vase!

Depending on the variety, you may consider growing the tall Mammoth Grey Stripe. For colorful dwarf varieties, try the Ring of Fire.  Some sunflower varieties have amusing names like the Teddy Bear, which appears fluffy and full of yellow petals.  

Planting Sunflowers

The best time to plant sunflower seeds is in mid-spring once the threat of frost has passed. The seeds can be planted outside, in pots, or started inside in seedling trays. Sunflowers require a lot of light to grow, you will want to find a sunny location.  The great thing about sunflowers is that they can grow in any well-draining soil. 

Care

Sunflower bud
The sunflower bud almost looks like an artichoke before opening. Source: Larry Lamsa

Sunflowers are easy to grow and require little care.  Let’s cover some essential growing tips so that you can plant sunflowers this upcoming growing season!

Sun and Temperature

Sunflowers thrive in full sun, with a minimum of 6 hours. USDA hardiness zones range from 2-11.  The ideal soil temperature for planting is 50-60 degrees Fahrenheit, and the optimum growing temperature ranges between 70-78 degrees Fahrenheit.  A sunflower is heat tolerant but is not as tolerant to cold temperatures and should be planted at the start of the growing season after the last frost date.   

Water and Humidity

The best time of the day to water is in the morning or evening. From sunflower seed germination until the plants are 2 feet tall, frequent watering is required. Focus on the soil 3-4 inches away from the stalk.  

Since this is a drought-tolerant plant, consistent watering is not required once the roots are established. The most important time to provide water to your sunflower is 20 days before and after flowering.  

Yet to maximize growth, water deeply 1-2 times a week with 2-3 gallons of water  Check the top inch of soil around the sunflower and if it is dry, it is ready to be watered. 

When you are watering your plants, you will want to focus on the root zone spanning 6-12 inches from the stalk and provide a gentle source of water.  You can use a rose attachment to your watering can, soaker hose or sprinkler setting on your hose.  Additional humidity is not necessary. Potted sunflower plants require more water as they are more susceptible to drying out.  

Soil

Sunflowers are incredibly resilient plants and can tolerate most soil types.  The ideal soil conditions are rich well-drained sandy soils, yet they are found growing in silt, clay, chalk, and poor depleted soils. Amend the soil with mulch, compost, or an alternative soil type to encourage proper drainage.  Sunflowers are tolerant of alkaline and slightly acidic soils, with the optimal growth range of ph 6.0-6.8. 

Fertilizing

Sunflowers have little to no need for fertilizer.  Poor soils can benefit from the application of compost, manure, or a slow-release 5-10-10 granular fertilizer.  Apply when you are sowing the sunflower seeds, and weekly during the seedling stage.  Water thoroughly. 

Pruning

Annual sunflowers will not reproduce another flower head once it is removed. Pruning is not necessary unless you want to trim off diseased leaves or old buds.  

Propagation

The only way sunflowers grow is through their seeds. Sow the sunflower seeds an inch deep, and gently cover them with soil. 

To sow seeds directly into a garden or raised bed, break up any compacted soil. Broadcast the seeds and cover. Alternatively, dig shallow holes 6 inches apart, place 2-3 seeds in the hole, and cover. You will want to gently water the area and keep the ground moist as seedlings emerge.  

For indoor seedlings, start 4-6 weeks before the last frost date.  Transplant in a larger pot in 3 weeks once their true leaves are developed.  About a week after transplanting, when seedlings are 6 inches tall, you can start hardening off the seedlings for 1-2 weeks. To harden off the seedlings, place them outdoors in a sunny protected location each day and bring them back inside at night.  

With potted sunflowers, use well-drained potting soil.  Smaller varieties can be placed in 12-inch pots, tall sunflowers will need a large 3-5 gallon pot. Be sure to water frequently. 

Harvesting and Storing

Sunflower florets in bloom
The many florets inside the sunflower head all burst into flower. Source: fdecomite

Many grow the sunflower in their garden for ornamental purposes because the seeds provide food for the birds.  If you are interested in harvesting the seeds, you will need to protect your seeds from birds.  Let’s explore some ways to enjoy your fresh harvest!

Harvesting

In early fall once the flowers have faded and are drying out, the seeds are fully ripened and ready to harvest.  You can cut the single stem 2 inches below the bloom. Another option is to harvest the heads when the seeds are partially ripened.  Leave about 6 inches of the stem attached to the bloom. 

Storing

When you harvest fully ripened sunflowers, you can rub the seeds out using the palm of your hand.  The seeds will pop out and you can lay them out to dry completely before you store them.

Flowers with partially ripened seeds can be wrapped in a paper bag and hung upside down in a well-ventilated area to dry.  You can harvest the seeds in a few weeks. 

Once your seeds have dried, they are ready to be stored in an air-tight container in a cool, dark place.  Now the seeds are ready to eat or for your garden!

Troubleshooting

Seeds starting to form
Seeds are starting to form in this flower. Source: nicksarebi

Some issues may come up when you are growing sunflowers.  They may be a climate issue, such as too much water or not enough sunlight.  Other problems include pests or diseases that are inhibiting the growth of your plants.  Let’s explore some common issues and how to treat them.

Growing Problems

Cold temperatures and frost can stunt or damage your sunflowers.  If seedlings started indoors, appear leggy and droopy, they may have been planted too early in the season.  Provide sturdy support such as a popsicle stick.  Once the weather warms, put the plants in a protected sunny location to harden off.

Problems with tall stems may occur.  If the plant is overwatered, stems will start to rot and turn brown.  Reduce watering and allow for the topsoil to dry out. Stems may bend or break from rapid growth or windy conditions.  Support the stalk with a tall stake to stabilize the plant. 

Issues with the flowers can be from under-watering, not enough sunlight, or too much fertilizerWilting flower heads indicate that the plant needs to be watered.  If flower heads are not developing, there may be too much fertilizer or not enough sunlight exposure.  Try to plant in a sunny location and water frequently. 

Pests

Common animals you may see around sunflowers are birds and squirrels.  To protect your seed crop, you will want to cover the heads with netting.  You can trim away the closest leaves to the flower heads to limit access for birds to perch. 

Insect pests include the gray sunflower moth, cutworm, leaf miners, and aphids. The gray sunflower moths feed on the florets, you will see small holes in seeds and possibly webbing over the flowers. Cutworms are about 2 inches long when mature and curl into a c-shape.  They are found in the soil and eat the stem of the sunflower under the soil. Leaf miners will eat a tunnel inside the leaves and create a small wiggly trail.

Aphids may be found on your sunflower.  They can produce a sticky sap that attracts ants and can spread other diseases.  Overfertilizing your plant so that it produces lots of leafy growth can attract aphids. A quick solution is to gently spray your sunflower with water and brush off the aphids.  

If you’re like me, you may want to manually eradicate the insects by hand and remove damaged plant parts with sanitized garden tools.  If infestation continues, BT (Bacillus thuringiensis) can be used on the sunflower moth, cutworms, and leaf miners.  Neem oil can slow down the egg production of leaf miners and aphids. Botanical-based insecticides like pyrethrins can be used on aggressive infestations of the sunflower moth or aphids.  

Apply insecticides in the early morning or late evening.  This will minimize the harmful impact on helpful pollinators such as bees. 

Diseases

The sunflower can be susceptible to powdery mildew, leaf rust, and fungal diseases.  Powdery mildew occurs from damp conditions and alters the leaf surface.  The leaves may turn pale and have mold that grows on the underside. Prune off damaged leaves with sanitized garden tools and let the topsoil dry out between waterings.  If the disease persists, you may want to apply neem oil or a copper fungicide. 

Other diseases that may infect your plants are rust and fungal leaf spots. This will appear as light yellow or white spots that will darken, and rust may include small blisters on the underside of the leaf. To treat, the plants require proper air circulation.  Make sure your plants are not spaced closely and trim crowded leaves. You will need to trim infected leaves with sanitized garden tools. If the disease is severe, you may choose to apply a sulfur or copper-based fungicide.

Frequently Asked Questions

Field of sunflowers
Commercial sunflower fields look like a sea of bright color. Source: jabberwock

Q: How long do sunflowers take to grow?

A: An average of 125 days. 

Q: Can you grow sunflowers in pots?

A: Yes you can!  Smaller varieties need a 12-inch pot, taller varieties require a large 3-5 gallon pot. 

Q: Where do sunflowers grow best?

A: Sunflowers can grow practically anywhere that has full sunlight.  They are a great low-maintenance plant and can thrive in poor soils and neglect.


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