How to tell if sunflower seeds are good for planting

Ready to plant sunflowers? Find out the best time to sow the seeds, how much sun they need, right soil type, good and bad companion plants, plus care and harvest tips for growing these annual flowers.

If you specifically want to grow really tall sunflowers or sunflowers with giant flower heads, see 12 Tips for Growing Giant Sunflowers.

Growing Sunflowers

Sunflower | Helianthus annuus

Sunflower Growing Guide
Annual or perennial flowering plant
• Full sun 6-8 hours per day
• Well-draining soil
• Ideal seed sowing soil temperature:
70° to 75°F (21° to 25°C) after risk of frost has passed

Shop Online: Buy sunflower seeds | Botanical Interests (US shipping)

Sunflowers are easy to grow and often the only challenge is preventing wildlife like birds and squirrels from stealing the freshly sown seeds. But, not to worry, I have tips for this below.

Once the plant is past the seedling stage, sunflowers are good, sun-tolerant plants that require minimal care.

Because they are annuals, you will need to sow new seeds each year. Some may self-seed as well. Don’t be surprised if the blooms are a bit different than the parent they came from: that’s normal for hybrid seeds.

Contents

1. Growing Tips
2. Choosing Seeds
   Sunflower Seed Buying Tips
3. When to Plant
   How late can you plant sunflowers?
4. Where to Plant
5. How to Plant Sunflower Seeds
6. Companion Planting
7. Growing in Containers
8. Pests and Diseases
9. Sunflower Care
10. Harvesting Sunflowers
11. Frequently Asked Questions
12. Resources

Empress of Dirt

Sunflower Growing Tips

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1Growing Tips

• Full sun:  6 to 8 hours a day is ideal in a location protected from the wind.
• Soil: rich, well-drained soil.
• Sow seeds: after risk of frost has passed.
  • Okay soil temperature: 55°F (13°C) or warmer.
  • Ideal soil temperature: 70° to 75°F (21° to 25°C).
• Sowing instructions: check your seed packet.
  • Usually 1-inch deep, spacing seeds 6 to 36 inches, depending on variety.
• Germination: 2 to 10 days.
• Days to maturity: 80 to 120 days.
• Container growing: yes, best for smaller, dwarf varieties.
• Fertilizer: amend soil with good compost. Can also use granular, slow-release fertilizer as directed on product label.
• Growing zones: Sunflowers are native to North America and can be grown as annuals everywhere from Alaska to Mexico.
  • Also grow in Europe, Australia, New Zealand and other sunny areas.

2Choosing Seeds

With over 70 species and lots of varieties, there are many choices!

How tall do sunflowers grow?

Sunflowers range in height from just one-foot tall to the “giant” varieties which can reach 15-feet (4.5 m) or more. See Giant and Dwarf Seeds for growing different heights.

• Sizes range from dwarf types (1 to 2-feet tall) to mammoths (8 to 15 feet). The world record for sunflower height is currently 30 feet!
• Flower sizes can be a few inches and up to 20-inches in diameter.
• Flower colors: white, pale yellow, yellow, bright yellow, orange, bronze, rust, dark red, and bi-colored varieties.
• Appearance and texture: long petals, short petals, fluffy, elongated….
• Formation: single flower heads, multi-flower heads.
• Cut flowers: there are pollen-free types intended for cut flowers.
• Seeds: check the seed packet to know whether the plant will produce seeds and if they can be saved for sowing. Some hybrids are sterile.

If you live in a cold climate, choose varieties that grow from seed to maturity in the number of days available between last frost in spring and first frost in fall.

Most take between 50 and 120 days, but there are exceptions.

Sunflower Seed Buying Tips

Here are some sunflowers seeds at Botanical Interests (US Shipping).

Every type of sunflower is different and not all sunflowers produce edible seeds. Sunflowers may be bred for specific colors, heights, flower sizes, types of seed (for birds or humans), to be pollen-free, and more. Check your seed packets to see what yours has to offer.

Giant Sunflowers

If you want large sunflowers, watch for the words ‘mammoth’, ‘giant’, ‘titan’, ‘monster’, or ‘tall’ in the names or descriptions.

I have a long list of recommended seeds for growing giant sunflowers here.

Sometimes these adjectives mean the plant will grow tall, sometimes it means the flower head will be very large but the plant may not be particularly tall.

‘Sunzillas’ produce massive heads. Mammoths grow 12-feet tall. There are many other hybrids developed to grow taller.

Dwarf Sunflowers

These are the ones that grow nicely in containers because they do not need the root space that larger ones do.

I’ve listed suggested varieties in the section on growing sunflowers in containers.

SHOP FOR SUNFLOWER SEEDS HERE

Look for interesting varieties including dwarf, tall, massive, and colorful ones.

3When to Plant

With seeds selected that you know have time to go from seed to harvest in your growing season, you can sow the seeds as soon as the risk of frost has passed for the season.

If you have time, you will get the best germination rates if you wait until soil temperatures are consistently 70° to 75°F (21° to 25°C).

But, for many of us, we need to sow sooner, and you can get by with soil temperatures of 55°F (13°C) or warmer—just be sure to protect them from critters and cover them if temperatures drop.

I’ve had late frosts after sowing but the sunflower seeds survived fine because they had not sprouted yet. If you expect a frost after sowing, cover the soil with a blanket for the night (and don’t forget to remove it in the morning).

You can also start sunflower seeds indoor in small containers for transplanting outdoors, although it is preferable to sow them directly outdoors if possible.Wait until your young plants have at least two sets of true leaves and a sturdy stem before transplanting. The stronger the young plant, the better your odds.

How late can you plant sunflowers?

How late you can plant sunflowers depends on which type you are growing and where you are in the growing season.

Step one is to look up how many days you have between now and your average first frost in fall. You can look this up using the link below.

If, for example, there are 100 days until first frost, you may still have time plant a sunflower that matures in under that number of days—preferably with a buffer of a few weeks.

For the 100 day example, a variety that shows “days to maturity” around 75 days should do fine. This would allow a buffer period in case your weather is not optimal and allow for slower growth as the days shorten as we head into fall.

4Where to Plant

• Pick a full-sun location: 6 to 8 hours a day is ideal in a location protected from the wind.
• Provide fertile, well-drained soil amended with good compost. You can also add a granular, slow-release fertilizer.
• Sunflowers have large taproots that can grow deep in the soil.
• If something blocks the roots, the plant will not grow to its full potential size. This is why it’s best to only grow dwarf varieties in containers.

Can you grow sunflowers in grass?

No, not if you’re starting from seed because the grass will likely out-compete the seedling.

If you have established sunflowers in pots ready for transplanting, you can remove a section of the grass and plant there. It’s not ideal, though, because sunflowers are resource hogs and like some room around the roots. If you do try it, cover any bare soil around the sunflower in mulch to help prevent the grass from filling back in and keep the soil moist.

Related: 10 Flower Growing Secrets & Common Mistakes

5How to Plant

When you are ready, read your seed packet for specific instructions on how to plant sunflower seeds: different varieties have different needs.

Sunflower seeds average a germination rate of 75% so 3 out of every 4 should sprout.

• Generally, sunflower seeds are sown 1-inch deep, spacing the seeds 6 to 36-inches apart, depending on the variety.
• You can also sow several seeds close together and remove the weaker ones after a few weeks. This is called ‘thinning out’.

Related: How to Read Seed Packets

Spacing Examples

• In general, a mammoth (tall, giant) sunflower does best in good quality soil with no other plants within 24-inches (two feet) in any direction (a four-foot diameter circle of growing space).
• Smaller varieties of sunflowers are more forgiving, with some doing fine with just 6-inches of growing space (in all directions). But more is better.  The better the resources, the larger the plant can grow.

Protect Your Seeds

• After sowing, cover the soil with 1-2 inches of mulch on top of the garden soil to help keep moisture in.
• Protect newly planted seeds with cloches, dollar store mesh waste baskets, or anything that will keep birds, squirrels and mice from digging up the seeds or slugs from eating the seedlings.
  If you do cover your seeds/seedlings, be sure to check on them so they have water, air flow, and light (after germinating).

What do sunflower seedlings look like?

This image shows sunflower seedlings:

If you planted your sunflower seeds individually, they will resemble the image (above). You may also find clusters of them in your garden where chipmunks or squirrels buried a bunch of seeds.

Sometimes sunflowers also grow with the seed shell sitting on the seedling as shown in the image inset. It will eventually fall off and it’s just funny, not harmful in any way.

Fun Facts

A plant’s tendency to turn toward the sun is known as heliotropism.

During vegetative growth up until bud formation, sunflower stems track ths sun.

This movement stops after the bud stage, leaving the flowers in an east-facing position.

Read More: How Sunflowers Track the Sun

How much can a sunflower grow in a week?

It depends on what type you are growing. Assuming growing conditions are optimal, a sunflower that will be 6-feet tall at maturity in 85 days (12 weeks) would average 6-inches of growth a week. In reality, there will be slower and faster weeks depending on conditions and the growth phase.

A smaller variety of sunflower may grow just an inch or two a week.

A giant or mammoth variety may grow a foot per week.

Do sunflowers need support?

It depends. If you are growing average size sunflowers (up to approximately 6-feet) tall in a sheltered area, supports should not be needed.

If you are growing tall (mammoth) varieties or ones with giant (heavy) flowerheads, you may need some support. I grow the larger ones near a fence so I can secure the stem with ties (strips of torn up cotton t-shirts work well).

6Sunflower Companion Planting

Before we jump into this topic, I have to say that I think much of what is said about companion planting in the gardening world tends to be too vague to use as garden instruction—if it’s even factual—and often, it’s not.

If this topic interests you, the book Plant Partners by Jessica Walliser explores what the science tells us based on specific plant relationships (you can read an excerpt from Plant Partners here).

Beware of simple soundbites like ‘carrots love tomatoes’ because that really doesn’t tell us anything (and it’s not really accurate).

The most important thing for successful plant growing is to provide the basics: good soil, adequate light, water, air, and root space. What we often think is a companion planting conflict is more likely just competition for resources. Keep this in mind when you read this next section.

What is companion planting?

Plants are sensitive to their surroundings. Not just the soil quality, amount of sun, and moisture levels, but which other plants are growing nearby. In some cases, plants send out biochemicals to try and thwart other plants. This is known as allelopathy and the practice that accommodates it is called companion planting.

Allelopathy is a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms.

From a scientific perspective, allelopathy is difficult to prove in home garden settings. Much of what we hear is anecdotal.

With sunflowers, the thought is that they produce compounds that inhibit growth in some other plants, stopping seed germination and growth.

You may suspect this is happening when sunflower seed hulls (the shells of the seeds) accumulate below bird feeders, causing the grass lawn to die. The hulls are otherwise harmless, though, and gradually decompose.

Sunflower Foes

What not to grow with sunflowers

The two plants suspected to be negatively affected by sunflowers are:

• pole beans (that climb like vines)
• potatoes

Both may struggle if planted too close to sunflowers.

Sunflower Bros

Good companion plants according to other gardeners

Plants said to benefit from sunflowers growing nearby are:

• cucumbers
• corn
• peppers
• tomatoes
• soybeans

But, as said, there does not seem to be solid evidence of this and it’s best to focus on good plant spacing and providing suitable growing conditions. Every plant needs adequate root space to grow, and sunflowers are big resource hogs. If we focus on providing each plant with the required growing conditions, the rest sorts itself out.

Related: Science-Based Companion Planting Tips for Growing Vegetables

7Growing in Containers

Because larger sunflowers grow deep, tuberous roots, it’s best to only plant smaller varieties in smaller containers (under 10-inches wide).

As with most container growing, you will need to add  fertilizer to provide sufficient nutrients. I use organic, slow-release fertilizers.

Here’s some examples of sunflowers that grow well in containers:

• Big Smile
• Elf
• Pacino
• Sundance Kid
• Sunspot
• Teddy Bear

8Pests and Diseases

Critters

Seeds and Seedling Stage

I always have to protect my sunflowers after sowing or they will be stolen by the wild things!

Birds, squirrels, mice, chipmunks, and anything else with a beating heart may try to dig up or eat the seeds and seedlings.

I use glass cloches, wire waste baskets from the Dollar Store, old soda bottles, or whatever I can find to cover the seeds and keep them protected. The mesh waste baskets are my favorites while the plant is under 12-inches tall. You may need to secure the basket to the ground with a clip or tent peg.

If you do this, you do have to be mindful that the soil stays watered, and—if using a glass cloche—to be sure the inside does not overheat.

If voles or other tunnelling animals are the issue, consider growing in large pots instead of the ground.

Once the seedlings are a few inches tall, the mammals and birds tend to back off until seed harvest time.

If you have slugs and snails in your garden, they too may come looking for dinner.

Deer too will also eat sunflowers if they notice them. Other than deer fence, I don’t have a solution for that one.

Flowering and Seeding

The flowering phase is the next one to attract wildlife. That’s when the birds and squirrels and all their friends return, hoping to nosh on the seeds.

You can put net or organza bags over the flower heads to deter them. The old school way is to tie large paper bags around them. I find mesh gift bags definitely slows the critters down.

Insects

There are several insects that attack sunflowers including sunflower moths, thrips, whiteflies, and various caterpillars.

Mildew and More

Sunflowers are susceptible to a number of fungal diseases including mildews and rusts, white mold, and Verticillum wilt. It’s the combination of humid days and cooler nights that tends to cause the most trouble.

Because sunflowers are annuals, it may not be worthwhile to treat the problem. If it’s bad, I just remove the plant to prevent spreading and sow your seeds in a different location the following year.

9Sunflower Care

I regard sunflowers as low-maintenance plants. Once I’ve got them past the seedling stage, I usually do nothing other than watering any in containers.

Some growers like to add fertilizer when the flower heads are blooming (I do not), which generally takes place over a period of 5 to 10 days. This can also be a time where the plant takes up a lot of water and may need additional watering.

10 Harvesting Sunflowers

If you check your sunflowers during the main growth phase, you’ll notice that the stalks are green, unless there is drought or disease.

Once the plant starts working on seed production, the stalks start turning yellow.

When the seeds are ready for harvesting, the stalks are brown.

Not all varieties produce seeds so check before you sow if this is important.

You’ll also notice that as the plant matures, the flower head starts facing down toward the ground. That’s when all those seeds (up to 1400 on one flower head) start forming behind the little floret petals.

If you want to save the seeds, you will need to cover the flower heads, either with netting, organza, or a paper bag, to keep the critters from eating everything. Even then, I have a few squirrels who will suck on the seeds right through the netting!

It is also possible to harvest the flower heads earlier and hang them up to dry—again, somewhere where the critters can’t get them, and remove the seeds later.

All seeds should be cleaned and dried before storing, otherwise they get moldy. Some instructions advice gently boiling them in salted water before consumption.

The alternative is to simply leave your sunflowers in the garden. As winter sets in, those wild things living in your garden will appreciate the fuel.

More info: How to collect, dry and roast squash and sunflower seeds | OSU Extension Service

11Frequently Asked Questions

When is the best time to plant sunflowers?

The ideal time is after the risk of frost has passed and soil temperatures are 70° to 75°F (21° to 25°C).

You can also sow the seeds when the soil is consistently 55°F (13°C) or warmer. This just means germination will be slower.

What month do you plant sunflowers?

For many cold climate gardeners, June is the month to sow sunflower seeds directly outside. This is after last frost when the soil is warming up. Faster growing sunflowers may still have time to mature when planted in July.

Do sunflowers grow back year after year?

No, sunflowers are annuals not perennials. This means they complete their entire lifecycle in a single growing season. If seeds fall to the ground, they may survive the winter and sprout next year. Otherwise you need to sow fresh seeds each year.

Do sunflowers need a lot of sun?

Yes, they have ‘sun’ in the name because they are sun lovers and like 6 to 8 hours of full sun each day.

How late can I plant sunflowers?

This will depend on the variety you are growing and the date of your average first frost. Most sunflowers need between 50 and 120 days (3 to 4 months) from seed to maturity. Count how many days you have available before frosts set in and choose a variety that fits that timeline.

Are sunflowers hard to grow?

No. The main challenge is preventing wildlife from stealing the freshly sown seeds and eating the seedlings. From there, the main growing phase is low maintenance, where you may just need to water if conditions are dry, and fertilizer if soil is depleted. Once seeds start forming in the flower heads, you may need to cover the flowers to keep animals from eating all the seeds, unless you’re like me and that’s why you’re growing them.

Can I transplant sunflowers?

Maybe. The seedlings transplant okay, but, once the plant is larger, the roots are deep and quite sensitive. And because they have taproots, if the taproot breaks during transplanting, it’s game over. So, transplanting after seedling stage is at your own risk.

How deep do sunflower roots grow?

Some of the larger varieties can send roots down as deep as four feet. It all depends on the size of the sunflower and if the soil allows the roots to grow freely. Coincidentally, the farther the roots can go, the taller the sunflower can grow (for the big types).

When do sunflowers stop growing?

Sunflowers stop growing when the flowers begin turning to seed. During this phase, the stalks turn from green to yellow and then brown, and the flower heads start facing the ground instead of east.

Can I grow sunflowers in pots?

Yes but choose dwarf varieties with smaller roots for best results.

How do you grow giant sunflowers?

It starts with the right seeds—sunflower species proven to grow big and tall. From there, you need the right growing conditions including adequate fertilizer.

Can you grow sunflowers from cuttings?

No. The only way to grow sunflowers is from seeds. They cannot be propagated from cuttings.

Can sunflowers grow from bird seed?

Yes, bird seed mixes that include sunflower seeds can produce sunflowers. If the seeds fall to the ground and have the right growing conditions, they can sprout and grow into sunflowers. Sometimes animals also carry the sunflower seeds from the feeders and hide them. If you notice sunflowers popping up in your garden, an animal likely buried the seed at just the right depth and location for germination.

12Resources

Empress of Dirt

Sunflower Growing Tips

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~Melissa the Empress of Dirt ♛

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