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.
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 but keep in mind that hybrids may not be the same in appearance as their parent plants.
|1 Overview: Sunflower Growing Tips
2 Choosing Sunflower Seeds
|12 Frequently Asked Questions
Sunflower Growing 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.
- 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.
- 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.
With over 70 species, and lots of varieties, there are many choices!
- 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 colours: white, pale yellow, yellow, bright yellow, orange, bronze, rust, dark red, and bi-coloured 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.
If you live in a cold climate, you will want to 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.
You can look up your frost dates here:
- Frost Dates Calculator | This calculator at Almanac.com is simple to use.
Enter your city and state or province to find your first and last frost dates and number of frost-free days.
Every type of sunflower is different and not all sunflowers produce edible seeds. Sunflowers may be bred for specific colours, heights, flower sizes, types of seed (for birds or humans), and more. Check your seed packets to see what yours has to offer.
If you want large sunflowers, watch for the words ‘mammoth’, ‘giant’, ‘titan’, ‘monster’, or ‘tall’ in the names or descriptions.
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.
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.
See Sunflower Seeds at Amazon.com. I selected a bunch of interesting varieties including dwarf, tall, massive, and colourful ones.
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 will do fine with soil temperatures of 55°F (13°C) or warmer.
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.
- 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 grow dwarf varieties in containers.
Read your seed packet for specific instructions: 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’.
- 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, wire mesh cages, or anything that will keep birds, squirrels and mice from digging up the seeds or 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).
- If slugs and snails are an issue in your area, you may also want to use Sluggo to prevent them from eating your plants.
As sunflowers grow and form buds and flowers, their heads move throughout the day to face the sun.
Once mature, they remain facing the morning sun.
When the plant starts producing seeds, the green stalks turn yellow and then brown, and the flower heads start facing downward.
The tracking of the sun in young sunflowers is called heliotropism.
Watch for this when you grow your own sunflowers.
If you’ve familiar with the idea of companion planting, you know that 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.
Allelopathy is a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms.
Simply put, sunflowers produce compounds that inhibit growth in some other plants, stopping seed germination and growth.
You may also notice this when sunflower seed hulls (the shells of the seeds) cumulate below bird feeders, causing the grass lawn to die. The hulls are otherwise harmless, though, and gradually decompose.
The two plants known to be negatively affected by sunflowers are:
- pole beans (that climb like vines)
Both may struggle if planted too close to sunflowers.
Plants that benefit from sunflowers growing nearby are:
That said, do allow enough root space for each plant.
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
- Sundance Kid
- Teddy Bear
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 the seeds.
I use glass cloches, wire cages, old soda bottles, or whatever I can find to cover the seeds and keep them protected.
If you do this, you do have to be mindful that the soil stays watered, and the inside of the cloche does not overheat.
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. You can use a product like Sluggo, which is safe around pets, or create a barrier around the plants.
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 next phase is when sunflowers are flowering: that’s when the birds and squirrels and all their friends return, hoping to nosh on the seeds.
You can put net bags over the flower heads to deter them. The old school way is to tie large paper bags around them.
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.
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, 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.
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.
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 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.
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
1 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.
2 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.
3 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.
4 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 fertilize, if soil is not rich. 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.
5 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.
6 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).
7 When do sunflowers stop growing?
Sunflowers top 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.
8 Can I grow sunflowers in pots?
Yes. This section discusses growing sunflowers in containers and lists suggested varieties to try.
9 How do you grow giant sunflowers?
I’ve got 12 Tips for Growing Giant Sunflowers here. Basically, you have to choose the right seeds, provide the right growing conditions, and fertilize them.
10 Got any gift ideas for a sunflower fanatic?
Yes! See these 19 Gift Ideas for Sunflower Lovers. I bet you’ll find something you love.
- Sunflowers for Sunny Places | Institute of Agriculture and Natural Resources | Nebraska Extension in Lancaster County
~Melissa the Empress of Dirt ♛