12 Tips for Growing Giant Sunflowers

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Ever wonder how to grow giant sunflowers? These insider tips share how to pick the right seeds and provide the right conditions to grow tall sunflowers with massive flowers in your garden.

For more tips, also see How to Grow Sunflowers and What to Avoid.

How to Grow Giant Sunflowers

Every summer new photos appear of gardeners standing next to massive sunflowers in their gardens, reaching heights of 10 or 12 feet or more. Or massive flower heads measuring a few feet in diameter.

So what’s their secret?

For most, it’s not secret at all but simply following some basic must-dos.

If you are hoping the get in the Guinness Book of World Records, it’s probably going to take a lot of trial and error over a number of years. The current record-holder managed to grow a 30-foot sunflower, and that, reportedly, was after years of testing and selective seed-saving until he had incredible seed stock and a stellar growing season.

For the rest of us who may just want a fun conversation starter or to hold a friendly competition with a neighbor, these tips will help.

The first step is to pick your goal.

Do you just want the tallest sunflower possible? If so, there are varieties that grow straight up and produce relatively small flowers up top.
If you want great height and huge flowers, a variety like Paul Bunyan is a good choice. It can produce flowers that are 18-24-inches in diameter and reach heights of 15-18 feet! Crazy.
And, if you just want large flowers, there are several varieties that produce massive flower heads on average height stalks.

Along with the tips, I’ve listed seed suggestions.

You can get a copy of the free tip sheet in the Resources section.

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)

12 Tips for Growing Giant Sunflowers

Three different sunflowers in the garden with yellow, orange, and red petals.

1Choose the Right Seed

This is the most important tip: genetics matter! You have to start with a variety of sunflower that can grow tall. Forget the dwarf varieties (which do great in containers), and look for types with words like giant, mammoth, kong, tall, monster, and so on in the either the seed name or description.

While researching this, I noticed height listings vary—and I’m sure growing results do too—but choosing seeds with a name that sounds big is important.

SUNFLOWER NAMES It’s the wild west when it comes to sunflower names. Several seed companies may sell essentially the same sunflower seeds under different names or variations of a name, and sometimes they use the same name but, clearly, based on the images, it is not the same seed stock. So, check before you buy to be sure it’s the type you want.

All Big and Tall Sunflowers

These links go to Botanical Interests and Amazon but do check your favorite local seller for seeds first.

American Giant | 10-inch flowers | 16-feet tall| 65 to 80 days
| 8 to 10-feet tall
Evening Sun | 7-feet tall
Giganteus | 18-inch flowers | 12-feet tall
Kong Hybrid | 8 to 15-feet tall
Mammoth Greystripe |12-13-feet tall
Mongolian Giant Sunflower | 16-18-inch flowers | 12 to 14-feet tall
Moulin Rouge | 3-6-inch flowers | 5-7-feet tall
Original Sun | 10-feet tall | multiple branches
| 18-24-inch flowers | 15-18-feet tall
Pike’s Peak | 15-feet tall
Russian Giant or Mammoth | 20-inches flowers | 10-feet tall
Skyscraper sunflower | 14-inch flowers | 12-feet tall
Sunzilla | 12-16-feet tall
Titan| 12-feet tall
Treasure Mountain Hybrid | 8-10-inch flowers | 10-feet tall

Tall Sunflowers by Height

Paul Bunyan | 18-24-inch flowers | 15-18-feet tall
Sunzilla | 12-16-feet tall
American Giant | 10-inch flowers | 16-feet tall| 65 to 80 days
Pike’s Peak | 15-feet tall
Kong Hybrid | 8 to 15-feet tall
Mongolian Giant Sunflower | 16-18-inch flowers | 12 to 14-feet tall
Mammoth Greystripe (Heirloom) |12-13-feet tall
Titan| 12-feet tall
Skyscraper sunflower | 14-inch flowers | 12-feet tall
Giganteus | 18-inch flowers | 12-feet tall
Treasure Mountain Hybrid | 8-10-inch flowers | 10-feet tall
Russian Giant or Mammoth | 20-inches flowers | 10-feet tall
Original Sun | 10-feet tall | multiple branches
California Graystripe | 8 to 10-feet tall
Evening Sun | 7-feet tall
Full Sun Improved | 4-6-inch flowers | 5 to 7-feet tall
Moulin Rouge | 3-6-inch flowers | 5-7-feet tall

Tall Sunflowers with Large Flowers

Russian Giant or Mammoth | 20-inches flowers | 10-feet tall
Paul Bunyan | 18-24-inch flowers | 15-18-feet tall
Giganteus | 18-inch flowers | 12-feet tall
Mongolian Giant Sunflower | 16-18-inch flowers | 12 to 14-feet tall
American Giant | 10-inch flowers | 16-feet tall| 65 to 80 days
Skyscraper sunflower | 14-inch flowers | 12-feet tall

2 Grow in Full Sun

Sunflowers need a lot of sun! The ideal location provides 6-8 hours of sun a day in a sheltered location so there’s low risk of wind or storm damage.

Timing matters: this shows you how to know when to plant sunflower seeds.

3Grow in Ground

It’s all about root space! Growing giant sunflowers in the ground in rich, well-draining soil, free of rocks or tree roots, is key. Any obstacles in the soil will inhibit root (and plant) growth.

If you’re not sure if your soil is well-draining, use this easy test to check.

You can grow sunflowers in containers, but that’s best for dwarf varieties, not when size is the goal.

This has more tips for where to plant sunflower seeds.

4Provide Rich, Well-Draining Soil

I know, I know! We hear this all the time in gardening. But soil is key. Sunflowers are hungry plants, needing a lot of nutrients to grow those big flowers and thousands of seeds.

Step one is to provide nice, loamy soil. My garden soil is terrible, so I add loads of homemade compost to the soil to gradually build it up each year.

This has more tips for how to plant sunflower seeds.

5Allow Space

Most sunflowers can grow anywhere from 6 to 36-inches apart, but, when you want to grow giants, it’s best to allow as much room as you can—not just from each other but any neighboring plants including trees and shrubs.

Allow space for the roots to spread several feet in any direction, both horizontally and down into the ground.

See this list for plants that don’t grow well near sunflowers and others that do.

6Provide a Wind Break

Giant sunflower growing next to an apartment building wall. — Giant sunflower growing next to a brick wall

The taller the sunflower, the more vulnerable it is to wind breakage or snapping under the weight of a climbing squirrel.

If you can, grow your sunflowers near a tall fence or wall, out of direct wind.

7Mulch After Sowing

While sunflowers do not like swampy soil, neither will they tolerate drying out. An inch of two of compost or finely chopped bark mulch will help keep moisture in and gradually decompose to amend your soil.

8Add Support

If you are going to add any support stakes or tall cages, it’s best to add them when the sunflower is young and the roots are small.

The older sunflowers get, the fussier they get, so any disruptions later on should be avoided.

9Outsmart Pests

The number one killer of sunflowers is pests! The problem begins after sowing seeds. Birds, squirrels, mice, and all their distant cousins smell those seeds from far and wide and come ready for a snack.

At seedling stage, birds fine them irresistible. Cutworms can also take them down.

Place covers over germinating sunflower seeds and keep them protected until they are several inches tall at least. Options for protecting the seeds and seedlings include fine wire cloches, dollar store mesh waste baskets, or lightweight frost cloths.

On the flip side, the hungry critters return when the flower heads start turning to seed. Use bags or netting to protect the flower heads. Or let them dine.

10Fertilize

Besides choosing super seeds, proven to grow big and/or tall, adequate nutrition is key to maximizing the height.

As with all gardening, the quality of your soil matters. Is it already rich in organic matter or is it lacking?

Personally, I am very cautious with fertilizers because of the environmental repercussions, so do your homework first. Personally, I avoid synthetic fertilizers and choose organic, slow-release amendments with care.

I have not tried any of these things, but here’s what others say they use: compost, kelp, fish fertilizer, and a product like Osmocote.

I also found tips specifically for encouraging extraordinary growth saying to dig shallow trenches in circles around the plant—about 12 to 18-inches out, and add liquid fertilizer there, to reach more of the roots.

It’s easy to over-do fertilizer, hurting both the plant and the soil so follow the instructions on any product you use. And if your soil is already rich, you may not need any. More is not more with plants: they can only absorb what they need when they need it under the right conditions and surplus can harm the environment.

11Water

I mentioned that sunflowers do not like to dry out—or get waterlogged—and that means keeping the water nice and even, right through the growing season.

As the plant gets tall and starts to bud, you may notice that sunflowers start needing more water. You may need to increase your watering routine, especially during dry spells and heat waves, which tend to go together. If you’re worried about over or under watering, a moisture meter is your best friend.

12Pinch Side Shoots

This is an extra tip if you really want height beyond anything else. To keep your sunflower putting all its energy toward height, you can remove any extra side shoots, and grow just single stalk with a flower on top. You will end up with a giant bean pole, but, if this is what makes you win the neighborhood contest, so be it.

TIP: Chickens love to eat sunflower leaves!