Giant Sunflower – Facts, Grow and Care Guide

Giant Sunflower is one of the largest and showiest of the perennial sunflowers you can grow in your garden.  Just when you think the only flowers left to bloom are purple asters…….. and then BAM.  All of a sudden you are treated to a huge display of golden yellow flowers that seemingly explodes seemingly overnight.  Also known as Tall Sunflower, this is a perennial sunflower and member of the Daisy Family. helianthus giganteus giant sunflower

 

 Facts

  • Long bloom time – Giant Sunflower can bloom for 1-2 months late in the season
  • Giant Sunflower is host to several varieties of butterfly.
  • Helianthus Giganteus is native to North America, from Minnesota, South along the Mississippi River to the state of Mississippi.  And then East to the Atlantic Ocean.
  • This plant is hardy from zones 3-9, check your USDA garden zone here.

Physical Description

As the common name would imply, it is BIG.  Helianthus Giganteus will grow 8-10 feet (2.5-3 m) tall in optimum conditions, in and open meadows of prairie in moist conditions.  They are easy to grow and establish, and will form a large clump several feet in diameter when mature.

Stalk / Stem

The purple/red stalk won’t have branches except near the top, where several stems will form.  White hairs will be present on it.

Leaves

There will be pairs of alternate leaves that are narrow and lance shaped.  The leaves will be serrated and slender, being about 4-7″ long and approximately 1″ wide.  The leaves feel kind of rough and have small hairs on them.

Flower

Each stalk will produce several flowers about 3″ diameter, give or take.  They resemble the ‘sun’, and are daisy-like.  They are a really bright and prominent shade of yellow.  You can expect the blooms to last for a month or two, depending on conditions.  helianthus giganteus

Root

The root is fibrous, and has rhizomes.  A single plant will form a small colony with these rhizomes, and crowd out nearby neighbors.  My ‘single’ mature plant is now a 3′ diameter colony.

Growing Conditions

Giant Sunflower like well drained moist soil and full sun.  The more sun and moisture (but well drained), the taller/larger the plant will get.  The final size of this plant is heavily dependent on the combination of soil, sun, and moisture.  With the more sun/moisture meaning larger plants.  It’s natural habitat is moist meadows, woodland clearings, and moist prairies.

How to care for the Giant Sunflower

The location you choose to grow this plant will be the single greatest factor in how much care will be required.  Giant Sunflower can be adapted to environments that aren’t the most suitable, if you put in the work to recreate its optimum conditions.

In general though, if you choose an open location that has a lot of sun exposure (6-10 hours) and moist soil, it won’t require any maintenance.

Maintenance

If this plant is exposed to lots of wind, the stems will be strong.  That will mean that by the time the blooms open, the flower won’t want to droop or flop over.  Another alternative is to stake the plant.  And finally, you can pack it in a dense backyard microprairie, where the stalks can be supported by other nearby grasses and flowers.  I’ve done this with Big Bluestem, False Sunflower, and a volunteer Late Boneset.  So, even though the stalks of my plant are well over 8′ tall, they hang down to about 6′ tall as they lean against these other plants.  So, I still get to enjoy the flowers, pollinators, and birds – but no work is required on my part.

This image shows how my flowers are supported by other, nearby plants

And finally, another trick to ‘flowers that flop-over’ is to just trim them earlier in the year.  This works well with Asters and other species.  All you do is cut the flower back by half its length a month or two before it blooms.  For example, if you trimmed this flower back to 2′ tall in early June, you would lower the final stalk height significantly, making the stem stronger and better able to handle the weight of the flowers.

Watering may be required if this plant is located in an area that is prone to drought.

How to Establish

helianthus giganteus seedling
Helianthus Giganteus Seedling

Growing Giant Sunflower from seed is probably your best option for getting it into your garden.  To do this, plant seeds 1/2″ deep in the garden in late Fall.  Or, winter-sow the seeds in pots.  You can also cold/moist stratify the seeds for at least 4 weeks prior to planting.

The key thing is that if you order seed online, make sure you plant them soon after you receive them.  These seeds should be stored in a sealed, refrigerated container.

How to Save Seed for Helianthus Giganteus

The birds absolutely love to eat the seed.  So you need to get there before them.  As soon as flowers fade, put an old nylon, or some kind of fine-mesh bag over the flower heads and tie it off.  Then after the seed heads have dried, store the seed in a sealed container in the refrigerator.

Reference Table

Giant Sunflower Reference Table
Common Name Giant Sunflower, Tall Sunflower
Scientific name Helianthus giganteus
Bloom Time Late Summer, Early Fall
Bloom Duration 3-6 weeks
Color Yellow
Bloom Size 3” diameter, daisy like flowers
Characteristics Multiple blooms perstalk, near the top
Height 8-10’ (2.5-10 m)
Spacing/Spread 4-6’ (1.3-2 m)
Light Requirements Full sun
Soil Types Well drained
Moisture Moist, medium
Maintenance Can require staking if not exposed to wind
Typical Use Wildflower gardens, large meadows
Fauna Associations Bees, seeds eaten by certain birds
Larval Host Silvery Checkerspot, Gorgone Checkerspot, Painted lady
Sowing Depth 1/2”, 12 mm
Stratification Sow in fall, winter sow, or 30 days stratification
Native Range USDA Zones 3-9
Notes Growitbuildit.com

Garden Uses

We have this plant in the rear of our backyard micro-prairie.  Click below to see how to create your own!

How To Make a Micro-Prairie

But, this plant is best in an isolated area, or some kind of wildflower garden.  I say this because it will form a clump quickly, even in its second year.  Due to its height, it must be planted in the ‘back’ of south facing garden, or else it will shade out anything behind it.  Also, if not exposed to wind, it will likely flop over, so you need to take steps I outlined previously to mitigate it.

Our Giant Sunflower plants are in the rear (North Side) of the micro-prairie. On the lower end of a slope, which ensures good moisture.

In the end, this plant is big and unruly, and I love it.  This is not a plant for a well-manicured flower bed.

Companion Plants

Some strong stemmed neighbors are a good choice for this plant, like Bluestem grasses or the Cup Plant.  To make beautiful color displays, try New England Aster, Aromatic Aster, and even Spotted Bee Balm.  The purple/pink colors will blend really nice with Giant Sunflower, really giving you a late-season pop of color.

Fauna

Tall Sunflower is a great plant for attracting late season pollinators to your garden.  I see many bees, butterflys, and other pollinating insects visit mine.  It is a larval host to several butterflies that prefer Helianthus (Sunflowers).helianthus giganteus tall sunflower

After blooming, this plant will get mobbed by Goldfinches eating the seeds.  So, if you want to save seeds – you better get there before the birds!  You can use a small netted bag to cover flowers after blooming to save seed.

Pests and diseases

I’m happy to report that deer don’t seem to eat this perennial sunflower!  Also, I’ve never noticed rabbit damage so that is great!

For other pests, there are a number of insects that will feed on the foliage and roots. But due to its size, this most likely won’t result in significant damage.

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