How Big Do Mammoth Sunflowers Get?

How Big Do Mammoth Sunflowers Get?

Sunflowers are one of the most iconic and easily recognizable flowers. With their bright yellow petals and tall stalks, they can brighten up any garden or yard. But did you know there’s an even bigger, bolder version of the classic sunflower? Enter mammoth sunflowers.

Mammoth sunflowers, also known as giant sunflowers, are aptly named; they truly live up to their mammoth moniker. While a typical sunflower may only grow to be a few feet tall, mammoth sunflowers explode upwards, easily towering over the average person’s height. If you want a flower that will become the star of your garden, mammoth sunflowers are just what you need.

In this article, we’ll dive into everything you need to know about growing mammoth sunflowers yourself, from when to plant them to how to care for them. We’ll also cover exactly how big these gentle giants can get and tips for enjoying their massive blooms all season.

How Big Do Mammoth Sunflowers Get?

The most obvious distinguishing feature of mammoth sunflowers is their sheer size. But just how tall do these flowers get?

On average, mammoth sunflower stalks grow between 8 and 12 feet tall. However, under the right conditions, they can reach astonishing heights of up to 14–16 feet or more!

To put this in perspective, the average person is between 5 and 6 feet tall. So a mammoth sunflower at full height could be over twice the size of a person—now that’s a mammoth flower!

The flower heads are equally as imposing. Mammoth sunflower blooms typically span 1 to 2 feet in diameter. Though some supersized flowers can have heads measuring over 2 feet across.

Once they reach their mature size, mammoth sunflower heads are too heavy to be supported upright on their stalks. Instead, they nod downward, like they are bending under the weight of their own mammoth proportions.

When to Plant Mammoth Sunflower Seeds

When to Plant Mammoth Sunflower Seeds

Now that you know just how big these flowers can get, you might be wondering when you should plant mammoth sunflower seeds to maximize their growth.

Mammoth sunflowers are heat lovers through and through. They will thrive during the warm temperatures and prolonged sunlight of summer.

To give them enough time to reach their towering heights, mammoth sunflower seeds should be sown directly in the garden 2-3 weeks after the last spring frost date. This timing ensures the soil has warmed up adequately for germination.

You can also get a head start by sowing mammoth sunflower seeds indoors 4-6 weeks before your frost date. Then transplant the seedlings into the garden once the danger of frost has passed. Just be careful not to overcrowd their indoor homes; even young mammoth sunflower seedlings need plenty of space for their roots to spread out.

Whichever method you choose, the key is to time plantings so that mammoth sunflowers can spend the entire summer stretching their stems upwards and developing their colossal flower heads.

Choosing the Best Spot for Your Mammoth Sunflowers

Sunflowers demand full sun to thrive, and mammoth sunflowers are no exception. For your flowers to achieve their maximum height and size potential, plant them where they will receive at least 8 hours of direct sunlight per day.

Mammoth sunflowers also develop massive root systems to anchor their towering heights and supply water and nutrients to their blooms. Make sure to plant them in an area with nutrient-rich soil loosened at least 1 foot deep so those roots have room to roam.

And since strong winds and heavy rain can damage blossoms and weaken stems, pick a somewhat sheltered location if possible. Just be sure the spot still allows for plenty of sunlight penetration.

Good options for siting mammoth sunflowers include:

  • Along a fence or structure that provides light wind protection
  • At the back of an ornamental flower border
  • In the corner of a vegetable garden
  • Next to a shed or garage that can act as a windbreak

How to Plant Mammoth Sunflower Seeds

Getting mammoth sunflower seeds off to the right start is key to growing strong, healthy plants. Here are a few tips for successful planting:

  • Dig holes 12–18 inches wide and deep where each seed will be planted. Mammoth sunflower roots need lots of room!
  • Fill holes with a mix of compost and soil to provide nutrition.
  • Plant 2-3 seeds together in each hole and cover with 1-2 inches of soil. Planting a few together improves the chances that at least one will germinate.
  • Space holes 18–24 inches apart to accommodate mature plants.
  • Water freshly planted seeds well and keep the soil moist but not saturated as they germinate. Expect sprouts in 7–14 days.

Once seedlings emerge, thin each group down to the single strongest plant. Snip off unwanted seedlings at the soil level rather than pulling them to avoid disturbing the remaining plant’s roots.

How to Care for Growing Mammoth Sunflowers

How to Care for Growing Mammoth Sunflowers

Caring for developing mammoth sunflowers is focused on keeping them consistently hydrated and competition-free. Follow these tips for success:

Watering: Mammoth sunflowers are thirsty plants! Water them at least 1-2 inches per week, and more in periods of heat or drought. Soak the entire root zone thoroughly when watering.

Weeding: Keep the area around mammoth sunflowers free of weeds, which compete for water and nutrients. Mulch after weeding to deter future weed growth.

Support: As mammoth sunflower stalks grow taller, their heavy flower heads cause them to tilt and bend. Stake plants or use trellises to provide support and keep them standing upright.

Fertilizer: Applying a balanced fertilizer monthly will fuel mammoth sunflowers’ rapid growth. Look for options labeled for vegetables or flowers.

Pests: Watch for insects like aphids, caterpillars, and spider mites, which can damage developing flowers. Use organic pest control measures if an infestation occurs.

Your mammoth sunflowers will likely meet or exceed average size expectations with attentive care and optimal growing conditions. It’s magical to watch them expand upward day by day throughout the summer!

Harvesting Mammoth Sunflower Blooms

One of the best parts of growing mammoth sunflowers is enjoying their spectacular blooms. The flower heads open from the outside rim inward over several days, eventually revealing a vibrant disk of golden yellow petals surrounding the center brown seed head.

Mammoth sunflower blooms are ready for cutting when the backside of the flower head has turned brown and you can see the first hint of yellow starting to show through between the petals. Cut the stem just above where it connects to the stalk using pruners or scissors.

To extend their beauty indoors, immediately place cut flowers in a vase of fresh water. Re-cut the stems every few days and change the water to help them last as long as possible. With proper care, cut mammoth sunflower blooms can often last up to two weeks!

In addition to cutting blooms, you can also allow flower heads to remain on plants until the seeds fully mature. Then the large seed heads can be harvested for eating or future planting. Just be prepared to provide extra support to accommodate their weight as the seeds develop.

Drying Mammoth Sunflower Heads

Drying Mammoth Sunflower Heads

Though fresh-cut mammoth sunflowers are undeniably stunning, you can also preserve their beauty by drying the flower heads. Dried arrangements are long-lasting mementos and can be created using a few simple steps:

  1. Wait to cut blooms until the backs are completely brown. This means seeds are mature, and drying will be easier.
  2. Remove excess stem length so just 6–12 inches remain below the flower head.
  3. Hang upside down or stand upright in a warm, dry, dark location with good airflow.
  4. Allow 1-3 weeks for drying. The flowers are ready when the petals appear dry and papery.
  5. Spray with clear acrylic sealer (optional) to help lock in color and prevent shedding.
  6. Display in a vase or work into wreaths, swags, and more!

Drying the huge blooms of mammoth sunflowers makes an even bolder statement than the flowers fresh from the garden.


If you’re seeking an eye-catching addition to your garden, look no further than mammoth sunflowers. With their towering heights and enormous golden blooms, they are guaranteed to make a mammoth impression.

By planting mammoth sunflower seeds at the right time, carefully tending the developing plants, and properly harvesting and preserving the flowers, you’ll be rewarded with these gentle giants’ spectacular summer show.

Mammoth sunflowers require minimal work for maximum impact. Just be sure to provide them with plenty of space to fulfill their mammoth potential! Allow these flowers to lift your spirits as they reach for the sun, and don’t forget to share them with neighbors and passersby so everyone can enjoy watching your mammoth sunflowers grow.

Common Questions

How long do mammoth sunflowers bloom?

Each individual flower lasts 5-7 days if left on the plant. But mammoth sunflowers will continually produce new blooms over several weeks. Remove spent flowers to encourage more blooming.

Do mammoth sunflowers come back every year?

Mammoth sunflowers are annuals, meaning they complete their life cycle in one season. You’ll need to replant seeds or seedlings each spring.

What kind of sun do mammoth sunflowers need?

Mammoth sunflowers require a minimum of 8 hours of direct sunlight daily. The morning sun is preferable to the afternoon sun.

How much space do mammoth sunflowers need?

When planting seeds or small starter plants, space them 18–24 inches apart. Mature plants will reach 4-6 feet or more across.

Do you need to stake mammoth sunflowers?

It is recommended to stake plants or use fencing or cages to provide support once they grow over 4 feet tall.

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