Last updated on October 21st, 2023 at 11:54 pm
Mammoth sunflowers are giant, stately sunflowers that grow very tall, and produce large, seed-filled flower heads at season’s end. If you are planting mammoth sunflower seeds for the first time, it’s important to use the right planting techniques, as well as to provide the right care for best blooming and height. Learn how to grow mammoth sunflowers, and get your giant sunflowers off to a great start.
What Are Mammoth Sunflowers?
All sunflower plants belong to the Family Asteraceae, and Genus Helianthus.
Within the Genus Helianthus there are approximately 70 different species of sunflower, consisting of both annuals and perennials.
The common sunflower is an annual sunflower, which grows from seed to bloom within the same season.
Helianthus annus is the species of sunflower that the mammoth sunflower varieties belong to.
This common sunflower has been hybridized over time to include a wide range of varieties. These range from dwarf varieties such as Dwarf Sunspot, to giant varieties, such as the Russian Mammoth.
Hybridization efforts are ongoing.
Mammoth sunflowers are included in these taller varieties, which can grow to impressive heights of 10 feet or more. The flowers are often very large as well, producing lots of seeds at the end of the season.
The tallest sunflower ever grown has been recorded in the Guinness Book Of World Records, measuring at 30 feet and 1 inch. This giant sunflower was grown by gardener Hans-Peter Schiffer of Germany in 2015.
There are different varieties of mammoth sunflowers, and most will take longer to grow from seed to bloom than the smaller varieties, which are often grown as cut flowers.
Mammoth sunflowers are most often grown for their impressive size, and their seed, which can be enjoyed by people, as well as wildlife and birds.
- Mammoth sunflowers usually produce a single flower at the top of a very tall stalk.
- Flowers of the mammoth sunflower varieties can grow to be very large, with an enormous head which is filled with edible seeds by the end of the season.
- The outer ray florets consist of the yellow petals. They are most often a bright yellow color, and are very decorative.
- The central or disc florets are generally brown, and highly fertile, allowing the plant to produce loads of seeds at season’s end.
- Seeds of the mammoth sunflower varieties are large.
- They are usually pale cream or white in color, and some varieties have a grey stripe.
- Depending on the variety, the seeds can measure from 1/2 to 1 inch in length.
- Leaves of the mammoth sunflowers are serrated and sticky, and grow opposite along the stem.
- The leaves are also coarse to the touch, from tiny hairs growing on the leaves themselves.
- These hairs serve a purpose, and help to conserve moisture for the plant during periods of drought.
- Stems on the giant or mammoth varieties of the common sunflower are often very thick and stiff.
- Stems are also covered in fine hairs, and generally unbranched, producing only one flower at the top of the stem as the plant develops.
- Sunflowers have long tap roots, which reach deep down into the soil.
- The deep roots will help to secure the tall sunflowers in place, along with the thick stems.
Different Varieties Of Mammoth Sunflowers
There are a number of different varieties of mammoth sized sunflowers available. Let’s have a look at some of the most popular varieties:
- The Russian Giant variety of sunflower can grow to a height of 10 feet.
- The flower on this sunflower can grow 12 inches in diameter.
- The seeds are great for roasting, and the birds love to eat from the sunflower heads in fall.
- Russian Mammoth sunflowers can grow to 12 feet in height.
- Flower heads on this annual plant can grow to 14 inches in diameter.
- The stems are thick and support the height of the flowers.
- Seeds are edible and great for roasting.
- The seed heads can also be used to feed the wild birds.
Mammoth Grey Striped
- Mammoth Grey Striped is another giant variety of the common sunflower.
- This heirloom sunflower can grow from 8 to 12 feet in height.
- Flowers are typically 8 to 12 inches in diameter.
- Seeds have a grey stripe at maturity.
- This sunflower will benefit from staking, and can be blown over in heavy winds.
- Seeds are great for roasting and feeding the wildlife.
- Giganteus is another giant, and thus the name is fitting for this mammoth sunflower.
- Stems grow from 10 to 12 feet in height.
- Flowers are approximately 8 to 10 inches in diameter.
- The flower stems are strong and sturdy, and wind resistant.
- This sunflower can reach heights of over 14 feet if grown in the right conditions.
- The flowers can produce huge heads, which can span 1 1/2 feet in diameter.
- Even the seeds are large, at 1 inch in length.
- The seeds are perfect for eating or feeding to the birds.
- This mammoth sunflower benefits from fertilizing and staking.
- Titan is an heirloom variety sunflower.
- The plant can reach 12 feet in height over the course of the season.
- The large sunflower heads can grow to be 24 inches across.
- Stems are thick and sturdy and are resistant to the wind. This plant will often stay upright without staking.
- This sunflower definitely benefits from fertilizing, due to the massive growth.
- Seeds are nutritious, and are great for the birds.
Planting Mammoth Sunflowers
Many moons ago, I started my sunflower seeds indoors, to give them a head start on the growing season. Our season is short, and we often have late spring frosts.
I thought that planting the seeds in June, after our last frost date, would be much too late, so I started my sunflowers earlier indoors in cell trays.
The sunflowers were transplanted into the garden when the weather warmed up. They grew to be about 2 feet in height.
Obviously stunted in growth, the little mini sunflowers were still pretty cute.
However, if you are growing mammoth sunflowers, you are likely expecting much taller flowers. No doubt you will be looking for the intended height of the variety that you are planting.
It is best not to plant the sunflowers in containers, and then to transplant into the garden, as this planting technique can cause stunting, and create much smaller flowers overall.
Therefore, if planting any sunflower, especially the mammoths, for best results direct sow the seeds into the garden.
- Sunflowers are heat loving plants, and do not tolerate cold and freezing temperatures. They are not frost hardy.
- Frost can cause damage to new and tender young seedlings, so it’s important to plant the seeds out after your last frost date in spring.
- To direct seed, plant in spring when the soil warms up, and the danger of frost has passed.
- Plant the seeds into a prepared garden bed, approximately 1/2 inch deep, and cover with soil.
- Ideally you would plant the seeds spacing them approximately six inches apart, and then after they have sprouted, thin the plants to the ideal spacing of 18 inches to 24 inches apart.
- This closer planting space makes up for any seeds that do not germinate, as well as any seeds stolen by wildlife, ensuring that there will not be big gaps between the final sunflowers left in place.
- If you do not have lots of seeds in your packet however, you can go ahead and plant the seeds 18 inches apart from the start.
- Water the soil after planting, and keep moist while the seeds are germinating.
- The mammoth sunflower seeds will generally germinate within 2 to 3 weeks, depending on the variety, the soil temperature, and the moisture in the soil.
How Long Do Mammoth Sunflowers Take To Bloom?
With proper planting and care, most mammoth sunflowers will bloom at about 90 days from germination. When in full bloom, the flower heads are fertilized by bees and other pollinators, and then seed production begins. When the seed head is mature, the seeds can be harvested, at approximately 120 days from planting.
Mammoth sunflowers will generally take the entire summer to grow from seed to bloom. However this does not mean that the plant growth is slow.
In fact, these sunflowers show amazing growth, and sometimes appear to grow inches a day, especially at the height of the growing season.
These giant sunflowers can grow up to 10 or even 14 feet in height, or more.
Blooming occurs after the plant has grown for about three months.
If planting multiple mammoth sunflowers, don’t be surprised if some plants bloom a little bit early, and some bloom a little later than the standard bloom time.
Each stem is unique, and has it’s own agenda. Blooming time is an approximation, in ideal conditions.
Once in full bloom, it’s seed making time, and the flower head continues to grow and develop, and form seeds.
Seeds are ready to be harvested once the sunflower seed head is mature, which is approximately 120 days from planting.
Mammoth Sunflower Care
Providing the right planting location and care for your mammoth sunflowers will result in best growth, blooming, and seed production.
- Mammoth sunflowers grow well in zones 2 to 11.
- Since these are annual flowers, the most important consideration for each growing zone is frost free days.
- If your growing zone has 120 days of frost free growing, then you will be able to have these sunflowers grow to maturity.
- Zones with a short growing season may not have enough time to grow the mammoth varieties to maturity.
- Check the usda plant hardiness zone map and the first and last frost dates calculator to determine frost free growing times.
- As per their delightful name, sunflowers not only look like the sun, they also love a sunny location.
- Grow in full sun for best growth.
- Sunflowers are easy to grow in most soil types, as long as there is good drainage.
- When planted in fertile and rich soil, which is full of organic matter, they will often show best growth.
- Sunflowers in general have deep tap roots and take a lot of nutrients from the soil. Repeated sunflower plantings will deplete the soil, unless amended and the nutrients are replaced.
- Mammoth sunflowers have massive growth, and need a lot of fertility to reach the maximum potential growth of the plant.
- Regular watering will contribute to the growth of mammoth sunflowers, especially when they are first starting out.
- That being said, if you live in a location that receives regular rainfall, the sunflowers can be left to the elements.
- Once the deep taproot has formed, the plants are more drought resistant.
- Watering during blooming and seed production will help with growth, and increase the potential for a bountiful outcome.
- Not all mammoth sunflowers need staking.
- Some varieties are sturdier than others.
- If you live in a windy location, staking can help to prevent toppling of your plants.
- This fall we had a hurricane, which pushed the mammoth sunflower stems flat to the ground. No amount of staking would have prevented this occurrence.
- Luckily all plants survived, and the sunflower heads continued to mature, producing seeds at the end of the season.
- Sunflowers are heavy feeders in general, and the larger they are, the more nutrients they will require for growth.
- Fertilize the mammoth sunflowers with a good organic fertilizer.
- Adding a few inches of compost to the garden bed will do wonders for the growth of these hungry plants.
- Consider comfrey fertilizer as well, as a natural and highly nutritious organic fertilizer.
Harvesting Mammoth Sunflowers For Seed Collection
At the end of the growing season, you will likely want to harvest your mammoth sunflower seed heads for seed collection.
When harvesting sunflower seeds, it’s important to make sure that the seeds are left to mature on the plant before harvesting.
There are telltale signs that the sunflower head is reaching maturity:
- A nodding seed head is sometimes a sign of maturity, however with the mammoth sunflowers this is not always the case.
- Often the sunflower heads on mammoth sunflowers are absolutely huge, and the heavy heads bend with the weight. Just because they are bending however, does not mean that they are mature.
- Looks for other signs as well.
- Another sign of maturity is the color on the back of the seed head. When the back of the sunflower seed head turns yellow or brown, this is a definite sign of maturity.
- You will also notice that the central disc florets easily brush off, and away from the seeds forming underneath. The outer ray florets have long since gone.
- Loose or missing seeds is another sign. The birds will know when the seeds are ready, and will often begin to feed on mature seed heads left standing in the field or garden.
Harvest the sunflower heads on a dry day, to prevent molding of the seeds.
Removing From The Stem
- To harvest your mammoth sunflower seeds, cut the stem down, so that you can reach the flower head.
- If you can reach the flower head, remove it from the stem by cutting it with a pair of snippers. Leave approximately 6 inches of stem attached if you plan to dry the sunflower heads for later use.
- I like to brush off all of the center disc florets from the face of the flowerhead right there in the garden. This can be a messy business, and it’s great to leave the mess in the garden.
- If you are planning to dry the sunflower heads, hang them in a safe place which is nice and dry, and away from access by wildlife.
- If you are not planning to dry out the individual sunflower heads, you can cut the stem close to the back of the flower.
- When harvesting multiple sunflower heads for seed collection, place them down individually onto a surface, such as into a box, or onto a large tray, so that they do not cover each other.
- Allow them to dry for a few days.
- Seeds can be harvested at any time, although often easier to harvest after the flower head is dried for several days.
Removing The Seeds
- Removing the seeds is quite easy, especially if they are pretty loose.
- Start at one edge of the sunflower head and nudge or push the seeds so that they pop out of place. As the seeds are removed, the process gets easier.
- Don’t be surprised if not all of the seeds are full, as some may be duds.
- However from my experience, if you are harvesting from mature mammoth sunflower seed heads, there should be lots of healthy seeds to collect.
- After removing the sunflower seeds from the flower head, it’s important to let them dry out.
- Lay the seeds in a single layer onto a baking sheet, or similar surface.
- Allow them to dry for at least twenty four hours or more before storing away.
- Store in a clean airtight container, or alternatively into a paper container, such as a large envelope or Kraft storage bag.
- If you have dried some whole sunflower heads intact, with the seeds in place, for feeding birds throughout the winter, store these seed heads in a dry place, such as inside a cardboard box in a single layer.
- These dried sunflower heads can also be individually wrapped in paper bags until ready to use.
- Avoid laying the dried seed heads on top of each other to prevent mold formation.
- Store seeds in a dry, cool and dark place.
With large flower heads and tall stature, mammoth sunflowers always make an impression.
These tall plants are perfect for the back of the vegetable garden, or planted along a sunny wall.
The large flowers produce loads of seed, and will help to feed the family, the wildlife, and hungry birds during the fall and winter months.
They are one of the easiest flowers to grow, and a good option for even the beginner gardener.
Next season I plan to plant a few new varieties of these giant mammoth sunflowers, to see just how tall I can get them to grow.
Have you ever tried to grow mammoth sunflowers? Be sure to leave a comment below to share your experience.