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Ultimate Guide to Growing Giant Sunflowers: Expert Tips from a Sunflower Breeder

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If you dream of nurturing sunflowers that reach skyscraping heights, take a cue from Dr. Tom Heaton. As a leading sunflower breeder and supplier for Renee’s Garden, Tom has spent three decades perfecting the art.

His innovations have brought a vibrant palette of sunflowers to gardens worldwide, ranging from deep burgundy to sunny yellow and even striking bicolors. His company primarily produces long-stemmed, pollen-free varieties perfect for both bouquets and garden displays.

Tom doesn’t just breed beautiful sunflowers; he also creates towering giants like the “Giant Edible Sunzilla” and the “Heirloom Titan,” ideal for those looking to make a mark in sunflower competitions.

Every year, he keeps a record of the tallest stalk and largest seed head he grows, storing them in his garage to compare with future contenders. His current record holders? A colossal 17-foot stalk and an impressive 24-inch-wide seed head!

In this guide, Tom generously unveils his secrets to cultivating these colossal sunflowers in your own backyard, aiming to help enthusiasts achieve new heights in their gardening adventures.

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What are giant sunflowers?

Sunflowers come in all sizes, but nothing beats the awe-inspiring presence of mammoth sunflowers! These towering beauties are perfect if you want to dazzle your family, impress your neighbors, or even captivate local wildlife.

What exactly makes a sunflower “giant”? It’s all about size and scale. Some varieties shoot up to great heights with impressively large heads, while others may not be as tall but boast colossal flower heads laden with seeds that become a feast for birds in the fall.

giant sunflower
Credit: Hoss Tools

Ever wonder how these giants reach such staggering sizes? They’re specially bred to have a longer growing period than their standard counterparts. By blooming later, they continue to expand, soaring in height or sprouting massive heads, sometimes achieving both.

The Mammoth Sunflower, an heirloom variety from North America, stands out with its huge, 14-inch-wide heads. These sunflowers can reach up to 12 feet in height with stalks as thick as young trees, robust enough to support their heavy, seed-filled heads.

For a sunflower that not only dominates the garden skyline but also provides a generous seed harvest, consider planting Mammoth Sunflower Seeds.

Growing sunflowers is simple and rewarding, making them a favorite among kids and a crucial resource for feeding wildlife. If you’re keen on supersizing your garden experience, why not try growing some giants?

Here at Harvest Savvy, we offer a fantastic selection of large varieties, and if you’re looking for tips on how to nurture these giants, you’re in the perfect spot.

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How to grow giant sunflowers

Growing giant sunflowers is a rewarding gardening project that begins with proper sowing. If you’re aiming for these majestic blooms, start by planting the seeds under glass using multipurpose compost around March to April.

As the weather warms and the threat of frost disappears, usually between April and June, you can transplant them outdoors. Expect your sunflowers to bloom from July through September.

Sunflowers are sun-lovers and need plenty of light to flourish, so choose a spot that receives full sun. To prevent your towering sunflowers from toppling over, pick a sheltered location and ensure their roots can dive deep for nutrients by enriching the soil with organic matter early on.

As they grow, support them with stakes, starting with a simple cane and upgrading to sturdier supports as necessary—these giants can soar over 4 meters and are vulnerable in windy conditions.

During their early growth, keep an eye out for slugs, which love young sunflower shoots. To protect your seeds, consider covering them with netting until they sprout, ensuring birds and critters don’t snatch them up. Water and feed your sunflowers regularly, using a tomato feed, to encourage robust growth.

For those preferring to start their sunflowers indoors, mammoth sunflower seeds are ideal. Planting them in biodegradable pots not only eases the transition when moving them outdoors but also protects the long taproots from becoming stunted.

Aim to transplant them within 2 to 3 weeks after sprouting to give them the best start in their final outdoor location. Keep the soil moist, but avoid waterlogging it, and you’ll see germination within 7 to 14 days. As the plants mature, they’ll prefer slightly drier conditions.

This method of growing giant sunflowers is straightforward and can dramatically enhance the aesthetic of your garden while providing a feast of seeds by season’s end. Whether you plant them for beauty or bounty, these giants of the flower world are sure to impress.

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Tips for Growing Giant Sunflowers

Each year, we’re amazed by photos of gardeners proudly posing next to towering sunflowers that stretch up to 10 or 12 feet tall, sporting flower heads spanning several feet across. You might wonder, how do they achieve such impressive heights?

The secret isn’t complicated – it mostly comes down to following a few fundamental gardening practices.

Hoping to break a world record with your sunflowers? That might require some perseverance. The record for the tallest sunflower stands at an impressive 30 feet, achieved after years of meticulous experimentation and selective breeding to perfect the seed quality under optimal growing conditions.

For those of us looking for a more lighthearted challenge – perhaps sparking some friendly neighborhood competition – here are some handy tips. Start by defining your goal:

  • Chasing the record for the tallest sunflower? Opt for varieties known for their sky-high growth and smaller blooms.
  • Want a sunflower with both impressive height and hefty flower heads? The ‘Paul Bunyan’ variety is a fantastic pick, capable of producing blooms 18-24 inches wide and reaching 15-18 feet tall.
  • Or, if massive blooms are your priority, consider varieties that yield large flowers on stalks of average height.

I’ve also included some seed recommendations to get you started. So, grab your gardening gloves, and let’s grow some show-stopping sunflowers this season!

Choose the Right Seed

Sunflowers, with their iconic golden petals and chocolatey centers, remain a favorite for gardeners aiming for size. These classic giants, often towering with tall, singular stalks and large, seed-laden faces that birds adore, epitomize the quintessential sunflower image for many.

Here’s a crucial piece of advice: genetics are key. To achieve towering heights, bypass the charming but short-statured dwarf varieties suited for containers and aim for those labeled as ‘giant,’ ‘mammoth,’ ‘kong,’ or similarly grandiose terms. These names aren’t just for show – they signify breeds capable of serious growth.

Giant Sunflower Seeds
Credit: etsy

In my research, I’ve found that the advertised height potential can vary, as will your actual results. Yet, opting for seeds that boast grandeur in their name is a good starting strategy.

I spoke with Tom, a veteran in the sunflower world, about why gardeners should choose his ‘Sunzilla’ seeds over traditional large varieties like ‘Mammoth’ or ‘Russian Mammoth.’ He explained that Sunzilla seeds are hybrids, crafted for uniform growth and reliability.

This means less guesswork when thinning seedlings, as each one has a solid chance of becoming a robust plant. Unlike older strains that can struggle with instability, Sunzilla is bred for a stout stalk to support its hefty blooms, capable of soaring up to 16 feet and sprouting massive seed heads under ideal conditions.

A final tip on navigating the seed market: it can be a bit like the wild west. Many companies may market similar or identical seeds under various names, or even the same name with differing stock. Always double-check to ensure you’re purchasing the specific type you desire. This small step can make a big difference in your sunflower success.

Grow in Full Sun

Sunflowers thrive under the sun’s generous rays, making them perfect for bright, sunny spots in your garden. For optimal growth, aim to plant them where they can bask in direct sunlight for at least 6-8 hours each day – the more sun exposure, the better.

These towering beauties, especially the mammoth varieties, crave the warmth and energy that only full, unfiltered sunlight can provide.

When choosing a spot for your sunflowers, consider their robust size. These giants can overshadow smaller plants, potentially blocking their sun. It’s also wise to pick a location somewhat protected from strong winds or heavy storms to prevent damage.

This strategic placement not only helps your sunflowers reach their full height but also ensures they contribute positively to your garden’s overall layout.

Grow in Full Sun
Credit: Orchid Flowers

Proper Soil Preparation is Critical

When it comes to growing towering sunflowers, the secret lies beneath the surface – in the roots. For these giants to reach their full potential, they need expansive, unobstructed space in rich, well-draining soil. This means avoiding any areas with rocks or nearby tree roots that could stunt their growth.

While it’s possible to cultivate sunflowers in pots, this method suits the smaller, dwarf varieties rather than the mammoth ones that aspire to the skies.

Let’s talk soil – it’s crucial. Sunflowers are robust feeders, craving plenty of nutrients to support their large blooms and abundant seeds. If your garden soil isn’t up to par, enhancing it with plenty of homemade compost each year can make a world of difference.

Mammoth sunflowers are somewhat forgiving, but they definitely perform better in nutrient-dense, warm soil. The ideal conditions for their seed germination are soil temperatures between 70º and 75ºF, with a pH level ranging from 6.0 to 7.5. It’s also vital to keep the area weed-free to prevent any competition for resources.

While sunflowers typically don’t require additional fertilizer, if you’re aiming for record-breaking heights, bolstering your soil with extra compost and a slow-release fertilizer can give them a significant boost. Remember, sunflowers develop deep taproots, so water them deeply but infrequently to encourage root growth and let the soil dry out between sessions.

Prepare your planting spot by digging a large area – about 2-3 feet across and 2 feet deep – to ensure the soil is loose and nutrient-rich. Since sunflowers are heavy feeders and exhaust the soil, you’ll need to replenish the nutrients annually. For a slow-release option, incorporate a granular fertilizer with trace minerals about 8 inches deep into the soil.

I use a mix of composted chicken manure and a balanced, slow-release fish fertilizer for an organic approach. You might also consider adding composted rabbit manure or an organic amendment like greensand or dried seaweed to enrich your soil fur ther, depending on its current condition.

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Allow Ample Space

When it comes to planting sunflowers, especially the mammoth varieties, spacing is key. These giants need a lot of room to truly flourish.

While sunflowers can typically be planted anywhere from 6 to 36 inches apart, for the mammoth types, the more space you provide, the better. This includes keeping them well away from trees, shrubs, and other plants that could impede their growth.

To ensure your mammoth sunflowers achieve their grand stature, allocate at least 18 inches between seeds when planting. As they grow, you might even consider thinning them out to about 36 inches apart. This variety tends to grow one large flower per stalk without any side branches, so ample space is crucial for developing full, robust heads.

Mammoth sunflowers can reach towering heights, which also makes them susceptible to damage from wind or even a curious squirrel’s weight.

To safeguard these lofty blooms, consider positioning them near a sturdy fence or wall where they can enjoy some protection from direct wind. This strategic placement not only supports their growth but also minimizes the risk of breakage.

planting sunflowers
Credit: Sow Right Seeds

The Right Way to Sow and Thin for Successful Sunflower Growth

To grow the largest sunflowers, it’s best to plant the seeds directly in your garden soil rather than starting them in pots. Sunflowers develop extensive taproots that can become restricted and stunted in containers.

Peat pots, in particular, tend to dry out and hinder root expansion. Additionally, despite gardeners’ intentions, transplanting is often delayed, so it’s more effective to sow seeds outdoors from the start.

For those aiming to cultivate giant sunflowers, timing and spacing are crucial. Plant the seeds early in the season—right after the last frost when nighttime temperatures consistently stay above 50°F (10°C). In cooler regions with short growing seasons, this typically means planting from late May to early June.

Ideal spacing for these giants is about 20 inches (50 cm) apart in rows. Closer planting may yield taller stalks with smaller heads, while wider spacing can lead to larger but potentially too heavy seed heads. If space is limited, planting in a tight clump and later thinning to one strong plant can also work effectively.

When sowing, moisten the soil, and plant the seeds about 1 inch (2.5 cm) deep in groups of 5-6 seeds, spaced 6-8 inches (15-20 cm) apart. To protect the seeds from pests, encircle the clump with a non-toxic snail bait like Sluggo.

Covering the area loosely with netting helps safeguard the emerging seedlings from birds. Keep the soil moist, and you should see seedlings sprout within 5-10 days.

As they grow, thin the plants to ensure the strongest, most vigorous ones grow unimpeded: reduce to the top 3-4 at 3 inches (7.5 cm) tall, to 2 at a foot (30 cm) tall, and finally to the single best plant when they reach 2 feet (60 cm).

To maintain optimal soil moisture without waterlogging, a layer of compost or finely chopped bark mulch is beneficial. This not only helps retain moisture but also enriches the soil as it decomposes. Remember, consistent attention to spacing, watering, and thinning will set you on the path to cultivating a truly spectacular giant sunflower.

Fertilizing and Watering

For those eager to grow towering sunflowers, consistent feeding and watering are essential. When your sunflower is young, aim to water the root zone, which is about 3-4 inches (7.5-10 cm) from the plant base. Each week, it’s beneficial to provide roughly 2 gallons (7.5 liters) of diluted liquid fertilizer.

As the plant matures, create a doughnut-shaped trench about 18 inches (45 cm) from the stem and 4 inches (10 cm) deep, where you can add several gallons of diluted fertilizer weekly. Remember, sunflower roots can stretch up to 4 feet (1.2 m) deep, so avoid applying fertilizer directly on the stems to prevent rot.

The choice of high-quality seeds known for their size and robust growth is crucial, but providing them with the right nutrients is just as important. The condition of your soil can greatly influence growth. Is your soil rich in organic matter, or does it lack vital nutrients?

I’m quite mindful about using fertilizers due to environmental concerns. Personally, I opt for organic, slow-release options and steer clear of synthetics. From my research, other gardeners recommend using natural amendments like compost, kelp, and fish fertilizer, or products like Osmocote for their nutrient value.

For exceptional growth, some gardeners suggest digging shallow circular trenches around the plant, approximately 12 to 18 inches (30-45 cm) out, and applying liquid fertilizer directly into these trenches to better reach the roots.

It’s crucial not to over-fertilize, as this can damage both the plant and the environment. Always follow product guidelines carefully. If your soil is already nutrient-rich, additional fertilizer might not be necessary. Plants absorb nutrients as needed, and excess can be detrimental.

For larger plants, an effective method involves creating several deep holes with a steel stake about 1½ feet (45 cm) away from the plant and roughly 3-4 feet (90 cm-1.2 m) deep. Fill these with diluted liquid fertilizer.

While some may use products like Miracle-Gro or Schultz’s solution, as an organic gardener, you might prefer a fish emulsion or similar organic fertilizer.

Sunflowers dislike extreme dry or wet conditions, so maintaining consistent moisture throughout the growing season is key. As they grow taller and begin to bud, their water needs may increase, particularly during dry, hot periods. If you’re unsure about watering levels, a moisture meter can be a reliable guide to prevent over or under-watering.

Adding Support

Giant sunflowers are stunning, but they can sometimes be toppled by strong winds due to their size. Although these sunflowers develop robust stems that can support their large blooms, a gust from the wrong direction can still knock them over, revealing their roots.

If this occurs, you might be able to salvage the plant by repositioning the stem and re-embedding the roots into the soil. Unfortunately, if the roots are severely damaged, they might not recover.

It’s wise to implement staking and other support strategies typically seen in flower farms, like using row strings and fences, early in the plant’s life to avoid root damage later on.

Adding Support
Credit: Pinterest

As Tom suggests, treat your giant sunflowers like family members. Pay close attention to weather forecasts, particularly as the plants grow taller and become more prone to tipping. On days with predicted high winds, hold off on watering to lessen the risk of them falling over.

While sunflowers generally don’t need staking, providing some support can be beneficial in areas prone to strong winds or in less-than-ideal growing conditions like excessive shade or cramped spaces.

If you decide to use stakes or large cages for support, it’s best to install them early while the sunflower is still young and the roots are undeveloped. Remember, as sunflowers age, they become less tolerant of disturbances, so it’s crucial to avoid any unnecessary interference with their roots as they grow.

Outsmarting Pests

Sunflowers often fall victim to pests, starting right from the moment you plant the seeds. Birds, squirrels, mice, and their various relatives can detect those seeds from afar and often drop by for a feast.

When the sunflowers are just tiny seedlings, birds find them particularly appealing, and cutworms pose another serious threat. To keep these eager pests at bay, consider covering your sprouting seeds.

You can use fine wire cloches, inexpensive mesh trash bins from the dollar store, or lightweight frost cloths to shield your seedlings until they’ve grown a few inches tall.

As the sunflowers mature and their heads begin to produce seeds, these hungry critters usually come back for more. At this stage, protecting the blooms with bags or netting can prevent them from being devoured, or you can choose to share a bit of your garden’s bounty with the wildlife.

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Harvesting Mammoth Sunflower Seeds for Eating

As your sunflower petals start to fall and the seeds inside begin to swell, it’s wise to protect these soon-to-be treats. Climb up a stepladder and gently cover the sunflower heads with either a mesh onion bag or a loose-fitting burlap or paper bag.

This simple step prevents birds from snatching your seeds, ensuring the heads remain pristine for showcasing at local fairs or simply for enjoying in your garden. Once the seeds develop a hard outer shell, indicating full maturity, cut the stalks from the base.

If you’re saving seeds for your bird feeder, allow them to dry thoroughly before manually removing them or using a wire mesh to help the process along. Keep these seeds in airtight containers to deter any pesky rodents.

Mammoth sunflowers are particularly worth saving. These sunflowers are known for their dynamic behavior; young sunflowers greet the sun in the east each morning and track it across the sky.

However, as they mature and their heads become laden with seeds, they will cease this movement and start to droop, signaling that the seeds are ready for harvest. Covering the flower heads with mesh or bags is crucial to protect these coveted seeds from wildlife.

When it’s time to harvest, you’ll notice the petals falling away and the green back of the head turning yellow. The seeds, initially white and soft, will mature to feature distinctive black and grey stripes. To ensure they reach full maturity, it may be necessary to bring them indoors to avoid freezing or wildlife interference.

Harvesting Mammoth Sunflower Seeds
Credit: Sow Right Seeds

For indoor drying, cut the stalk about a foot below the head and hang it upside down in a well-ventilated, dark space. This drying period can last several weeks. When ready, the seeds should easily rub off into a bowl or bucket.

If they resist, they may need more drying time. Remember, the seeds mature from the outer edges inward, so the center seeds might not develop fully—these are perfect for feeding birds.

For those who enjoy a tasty snack, raw or roasted mammoth sunflower seeds are a treat. Soaking them in salt water before roasting at 400°F for 10 minutes enhances their flavor, or you can roast them dry at 320°F for about 5 minutes. If you plan to replant seeds next season, ensure they are completely dry before storage, but don’t roast these!

Growing mammoth sunflowers is a rewarding endeavor. The towering plants and massive flower heads can make any gardener feel dwarfed, adding a magical element to your gardening experience.

Which Giant Sunflower Varieties are Best?

Sunflowers aren’t just the classic yellow giants we all envision; they come in an array of colors such as red, orange, green, and even white. You can choose from annual or perennial types, as well as sizes ranging from small to towering varieties.

One of the tallest breeds, known as ‘High Hopes,’ reaches an impressive 4.5 meters, dominating the garden scene from July through October.

For a fun family gardening project, consider the ‘Russian Giant.’ This variety is not only straightforward to cultivate but also grows to about 3 meters tall, featuring large 30cm wide flowers. These blooms are perfect for harvesting seeds, which kids can enjoy roasting for a nutritious treat, while birds relish the leftovers.

If you prefer something slightly shorter, ‘Astra Gold’ stands out with its unique golden, ruffled petals and is ideal for adding drama to the rear of a flower bed. It also makes an excellent choice for cut flowers.

Another dramatic addition is the ‘Solar Eclipse,’ with its vivid yellow petals edged in deep red, creating a stunning ‘ring of fire’ effect in your garden.

All Big and Tall Sunflowers

  • 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

If you’re aiming for the sky, Suttons offers several spectacular giant sunflower varieties:

  • Giraffe‘ truly lives up to its name, growing up to 5.2 meters. Bred over three decades by Victoria Wakefield, this sunflower stands out for its sky-scraping height.
  • Giant Yellow‘ is another tall variety, reaching between 1.8 and 2.7 meters. It’s noted for its large blooms and is edible, perfect for adding something extra to your summer salads.
  • Pike’s Peak‘ stands strong at 4.6 meters with a sturdy stem, making it ideal for windy spots. It also boasts large seeds, enjoyed by both birds and snack-loving gardeners.
  • Lastly, the ‘Titan‘ stretches up to 3.5 meters tall with massive flowers that are easy to grow and a favorite among kids. This pollen-free variety is also a boon for those with hay fever.

With such a diverse selection, there’s a sunflower for every garden and gardener.

Giant Fun for All Ages

If you’re chasing the tallest sunflower in the neighborhood, here’s a tip: prune any side shoots and let your sunflower grow one strong, single stalk. This method might leave you with what looks like a giant beanstalk, but it could be your ticket to winning the local garden contest!

Sunflowers are also fantastic for getting kids excited about gardening. Plus, the seeds are a hit with the birds, making your garden a haven for wildlife.

Want to spark a love of gardening in your children? Try planting giant Sunzilla sunflowers. Their rapid growth and large, lion-like flower heads are sure to capture the imagination, much like Jack’s beanstalk. These towering beauties are perfect for creating sunflower forests, playhouses, or even teepees in your garden.

For a twist, plant colorful vines like scarlet runner beans around them, giving the sunflowers a head start to support the climbing vines. It’s a great way to engage kids, watching their sunflowers soar in height each day or even setting up a friendly growth competition. I’m even planning to distribute seeds to neighbors to see whose sunflower reaches the sky first!

And don’t forget about mammoth sunflowers—they’re not just a sight to behold but also produce a bountiful harvest of tasty seeds, plenty for you and the birds to enjoy.

Found these tips useful? Why not share them with your gardening friends!

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