Helianthus Giganteus is an annual plant that proudly displays huge flowers with (more commonly) vibrant yellow petals and a golden-colored center that attracts a wide variety of life, including birds, bees, and butterflies.
Their flower heads can come in various colors, including cream, red, and chocolate brown, which adds an array of colors to your garden.
Sunflower stems are robust and can grow up to 12ft (3.6m) tall, which makes them the perfect, dramatic backdrop to a sunny flowerbed that perhaps backs onto a wall or fence.
Table of Contents
Mammoth Sunflower Plant Overview
| Scientific Name | Helianthus Giganteus |
| Common Names | Mammoth, sunflower, wild sunflower, giant sunflower |
| Genus | Genus Helianthus (Not to be mistaken with helianthus tuberosus) |
| Family | Asteraceae |
| Origin | North America and parts of Central America |
| Size and Dimensions (Mature) | 9ft-11ft tall |
| Distinguishing Features | Course, hairy, tall, and fast-growing annuals |
| In-Home Placement | In full sun / direct light |
Are Mammoth Sunflowers Perennials?
The Mammoth Sunflower does not come back every year. These plants are an annual, not a perennial variety of sunflower, and will not return from the roots during the following spring.
This means they grow for one season and flower for the next two to three months before dying for winter after the first frost.
However, Mammoth sunflowers seeds are plump, meaty, and fortunately plentiful, which can be harvested and, if stored correctly, can be regrown next spring or stored for a second or third year.
Although the Mammoth is an annual, there are many sunflowers of the perennial varieties. (See list below).
When to Plant Mammoth Sunflowers
Mammoth sunflowers are best planted in late spring after the first frost has occurred when the soil reaches 50 degrees Fahrenheit or warmer.
To maximize bloom time, you can continue to plant in succession through to early summer. They make great annual plants as they thrive in most seasons. Planting them during the late summer months can be too hot for them to grow correctly.
When planting your mammoth sunflower outdoors at any time of year, place it in a sunny area that receives lots of morning and afternoon sunlight on its large heads. Plant it near a south-facing wall or fence so it will receive more direct sunlight throughout its growing season.
You’ll need to water your new plants regularly until they become established (about one month). After this time frame, you should stop watering, except when there has been no rain for at least two weeks.
Sunflowers originate from North America and prefer a warmer climate, so if you live in a cooler region of the country or have a short growing season (like regions located in northern latitudes), your mammoth sunflower might struggle to survive.
Mammoth Sunflower Care and Growing Conditions
To care for your mammoth sunflowers properly, there are a few things to be aware of.
Soil
Mammoth sunflowers grow best in well-drained soil. They can tolerate dry soil, but it is best to plant them in a place you can easily access a source of water for the summer months, you will be watering them often! These golden beauties do not fare well in cold weather, so if possible, try to plant them after the last frost has occurred.
Mammoth sunflowers prefer a rich organic soil that drains well. Still, they can also tolerate clay soils if they are amended with compost or other organic matter to help improve drainage and aeration.
One thing to note is that they do not like sandy soil, so you should steer clear of using too much sand as a growing medium.
Water
Mammoth sunflowers need regular watering during dry weather. Make sure not to overwater!
When grown in a container, your plant may begin growing mold on top of its leaves if moisture sits at the bottom of its pot—this can be prevented by allowing excess moisture to drain out through drainage holes before replanting it back into its original container.
Temperature
The best temperature for these flowers to grow is between 65 and 85 degrees Fahrenheit. This will help produce vibrant, beautiful blooms.
Light
These flowers prefer 6-8 hours of sunlight per day! The more direct, the better.
Humidity
They can tolerate mild to high humidity.
USDA Hardiness Zones
Most are hardy in USDA zones 4 to 9.
Fertilizer
Mammoth sunflowers prefer manure. If you have a horse or cow, their manure will work just fine. If not, many places sell bags of it at a low price (or even free if you live in a rural area). The next best thing would be fertilizer which you can get from any local flower shop.
Consider amending nutrient-deficient soils with a DIY compost!
How to Propagate Mammoth Sunflowers
These annual varieties of sunflowers are one of the easiest flowers to grow. They tolerate different soil conditions and can grow in full sun or partial shade. Sunflowers require a lot of water, so make sure your containers have drainage holes and are regularly watered.
To ensure your sunflowers survive, plant them in early spring after the last frost date.
Soaking the small seed heads is an essential step in getting them to sprout.
- Soak the seeds for 24 hours before planting. This can also help with growing huge heads.
- Plant the sunflower seeds 1/4″ deep and 1″ apart in warm soil.
- Keep the seedbed moist but only wet once seedlings emerge, which can take up to three weeks or more, depending on temperatures and conditions.
- Once your plants have grown about 4 inches tall, thin out some of them if you need to so that they don’t crowd each other too much; otherwise, leave them alone! If you want the tallest sunflower, do not skip any steps!
Conditions Needed for Propagation
Plan Your Light Environment
The key to successful sunflower propagation is the light environment, which is critical for growth and development.
Sunflowers need bright light when propagated. They should be exposed to indirect and diffuse lighting that produces an average temperature of 65°F+ (13°C) during initial growing periods; however, some varieties can tolerate temperatures as low as 45°F (4°C).
It is an option to use grow lights and heat lamps during winter months indoors to ensure your plant is getting enough light and warmth.
Keep Humidity High Around Your Sunflower Seedlings (70-80%)
It’s important to keep your sunflower seedlings well-moistened but not wet. A cool mist sprayer or humidifier will help with this, but you can also mist the leaves of your plants regularly.
You’ll want to use a humidity tray if possible; this way, you can place it under each individual plant and ensure that all areas are kept at the proper level of moisture.
Use a Rich Soil Combination with Compost and Peat Moss
Sunflowers are a great plant to grow in your garden and thrive well in small spaces. They’re especially easy to grow if you have access to compost and peat moss. These two ingredients make up the richest soil for your sunflower seeds.
Compost is a good idea because it contains many nutrients which are essential for healthy plants. Peat moss, on the other hand, is rich in organic matter that allows water absorption from the soil when it rains or gets dry due to drought conditions.
If possible, get some organic material like this from your local farmer or yard waste center so that it has been treated with biodegradable pesticides before being added to your soil mixture!
Common Problems with Mammoth Sunflowers
The mammoth sunflower can grow into a massive plant with care and attention. But sometimes, things threaten the growth of your mammoth sunflower seeds.
Learn about some common problems with this plant below!
Powdery Mildew
If you’re seeing white, powdery mold on the undersides of your sunflower leaves, your plants likely have powdery mildew. It usually occurs on lower leaves first.
This fungal disease can be treated with a neem oil spray or sulfur spray, but the most effective is a solution of household baking soda which should kill the mildew quickly.
If you have a lot of space in your garden and good air circulation, try planting sunflowers in another area for next year, so they don’t get infected again!
Root Rot
If your plants are not growing normally, dig up one of the plants to check the roots. Healthy roots look like white carrots and smell nice. Diseased roots will smell bad and turn brown or black.
If your plant has root rot, it won’t recover even if you cut away all the bad parts of the root system, so it should be pulled up and discarded.
Fungal Disease
Fungi cause fungal diseases. Many different fungi, including powdery mildew, rust, and downy mildew, can cause fungal diseases which are spread in several ways and affect every single flower.
- Spores can blow onto your sunflowers and grow in the moist soil around them. If you have other plants that have been affected by fungus, it’s possible for spores from those plants to blow onto your sunflowers and cause an outbreak on them as well.
- Insects can carry fungal spores from one plant to another (or even from one part of a plant to another). In some cases, insects won’t actually eat any part of the plant; instead, they may just sit around on its leaves or stems until they die off—and then leave behind some fungal spores when they decompose!
- Water is another way that fungal diseases might spread through your garden; if it has been raining recently or if there has been extra moisture underground due to heavy rains earlier in the season (or even snowmelt), this could cause fungal spores on one plant’s leaves or stems from being splashed into nearby areas where other sunflowers are growing—or vice versa!
If you see any of these problems with your sunflowers, don’t panic! You can save your crop by removing affected plants and treating the rest with a fungicidal solution.
How to Harvest Mammoth Sunflowers
Wait until the backs of the sunflower blooms become green; this is usually around early fall. Once the backs of the sunflower blooms become green, it’s time to harvest. The plant will start to turn brown and die down, so don’t harvest too soon!
Choose a Sunny, Dry Day
Sunflowers need full sun to grow and thrive. If it is rainy or humid, the sunflowers will not open up as easily. Harvesting on a drizzly day can also cause your flowers to wilt. If you cannot pick on a sunny day, wait until the next one before harvesting your flowers so they have time to dry out after being cut off the plant.
- Cut off the bloom stalks above the seed heads by clipping them with pruning shears.
- Use pruning shears to cut the stalk at the base of the seed head, just above where it joins with leaves.
- Make sure not to cut too close to this point, or else you’ll prevent any seeds from forming!
Seed Storage
- Seeds should be collected and dried overnight or for several hours before storing.
- Once dried, place them in an airtight container which should then be labeled with the date you harvested them. This will ensure you have seeds for your following growing season, although your seeds can last for many years if stored correctly.
Can You Grow Mammoth Sunflowers Indoors?
You absolutely can. The best way to grow mammoth sunflowers indoors is in pots. This can be done inside or on a patio, deck, or balcony. If you plan to transplant them outdoors later, choose a location that receives full sun throughout the day and has well-drained soil. Sunflowers are native plants providing great seed production with high oil content, a fantastic food source, which makes this a wonderful type of product to plant near the kitchen.
Creative Ways to Display Mammoth Sunflowers Indoors
Let Them Grow Tumbling Out of a Large Clay Pot
Sunflowers can grow in a pot, but they need to be large. We recommend using a clay pot at least 10 inches tall and 8 inches wide to provide the most efficient way for the sunflowers to grow. The larger the pot, the better you want to give these sunflowers plenty of room to stretch their roots! If you are growing your flowers in a clay pot, they will need more watering than if in the ground but ensure there is good drainage.
A Tall Compost Bin or Trash Can
The compost bin or trash can should be large enough to accommodate your sunflower plant. The container should also be sturdy enough to hold the weight of a mature plant and have a drainage hole at the bottom.
Grow Them in an Old Wheelbarrow or Wagon
You can grow the mammoth sunflowers in an old wheelbarrow or use a wagon. You could also use a large pot or container.
11 Lovely Reasons to Grow Mammoth Sunflowers in Your Flower Garden
There are many reasons you should add Mammoth Sunflowers to your garden. Aside from the fact that they’re absolutely stunning flowers that can be used as a cut flower, their tall stalks and large petals offer shade for smaller plants in your garden, they attract pollinators which are necessary for healthy blooms, and they even make a natural bird feeder!
Below are 11 reasons to grow this type of sunflower.
1. They create shade.
Sunflowers can provide shade for your flower garden. You can plant these tall sunflowers in rows to create a natural barrier or along the edge of your pond or water feature. They are also great for providing shade for children playing in the garden.
2. You will attract pollinators to your garden.
Sunflowers are a great choice for the backyard garden. They attract bees and butterflies, which are essential to pollinate your other plants. Sunflowers are also a great source of pollen and nectar for these pollinators.
3. You can use the stalks as a trellis or teepee for smaller plants.
You can also use the sunflower stalks as a teepee for smaller plants. This works exceptionally well with tomatoes, pepper plants, and other annuals. The sunflowers will provide additional support to the plant, helping it grow strong and produce more fruit.
4. Mammoth Sunflowers create a natural bird feeder.
Sunflowers are a popular flower for many reasons, one being that they are a great source of food for birds. When the seeds mature and ripen, they fall off and become bird food. This process can be repeated over again until you’re ready to harvest your seeds for eating or cultivation purposes.
5. The leaves offer protection.
Besides being one of the most eye-catching flowers, these low-maintenance flowers also offer a number of benefits to your garden. One of these benefits is that the leaves provide protection from harsh weather conditions. If you’re growing sunflowers in an area where strong winds are common, their large leaves can be used as a windbreak for other plants in your garden. The leaves can also help shelter birds who have made their nests on top of them from rain and snow during cold seasons. However, be aware that heavy winds can catch their heads, causing breakage or other damage.
6. They are easy to grow in most areas!
These flowers grow in most areas and can tolerate drought and poor soil. If you are a beginner gardener, sunflowers are a great choice because they are fairly tolerant of mistakes. They can also be grown in containers or planted directly into the ground. You can even grow these stunning flowers from seeds or start with plants!
7. Harvest nutritious edible sunflower seeds to eat.
These edible seeds provide a storehouse of nutritional benefits, including protein and fiber. Sunflower seeds are also rich in vitamins C, E, and iron. They contain B vitamins and healthy fats that help to lower cholesterol levels and keep your heart healthy.
8. Support and restore soil health.
Sunflower seeds are a good source of nitrogen, which is a nutrient that helps plants produce flowers and fruits. When you grow them in your garden, sunflower seeds add organic matter to the soil, improving its fertility and structure. You can also use them as a cover crop or green manure by planting them in beds where you don’t want any other plants to grow for one season only. Sunflowers will help restore these areas by adding nutrients back into the soil before they are dug up again.
9. Make a sunflower house!
Sunflowers aren’t just beautiful; they’re also a great way to attract birds to your garden. If you want to add more birds and butterflies to your yard, try making a sunflower house! It doesn’t have to be anything fancy—just grab some twine and two sturdy sticks (use 2x4s for larger houses).
10. Birds love to nest near them.
Sunflowers are a favorite nesting site for birds because of their tall stalks and large leaves. During the months of summer heat when there aren’t many insects around—the main source of protein for birds—sunflower seeds provide an important source of nourishment that helps keep your feathered friends alive during this period when they usually have fewer resources available. Birds may also use part of the stem for nesting material.
11. Limit weeds and other invasive plants in your garden.
Sunflowers are allelopathic, which means they give off toxins from their roots, leaves, stems, seeds, and flowers that prevent the growth of other plants. They can even kill any new growth trying to take over your garden. This is a protective method used for the plant to help continue growth year after year.
If you have kids or pets who enjoy playing outside but don’t want pesticides being used around them either because of health concerns or environmental ones (or both!), this might be another reason why growing annual sunflowers could be just what you need!
Dwarf Varieties of Sunflowers
Short on space? Try growing single stalk, dwarf sunflower variety! These types of sunflowers are just like regular sunflowers with the same beautiful bright yellow petals, except they are smaller. They’re not a separate species of sunflower; they’re just a variety of plant that has been bred to grow shorter and bushier than their taller counterparts. This makes them easier to grow in small yards or containers (if you have a small yard and live in an apartment, for example) and also have small seeds which can still be eaten or harvested for future sewing.
Because dwarf sunflowers aren’t as tall as their larger counterparts, you don’t have to worry about them blocking out the sunlight from nearby plants—or casting shadows on your face when you’re trying to enjoy the summer heat outside!
Why Dwarf Sunflowers Are a Good Alternative
The compact size of dwarf sunflowers makes them a good choice and easier for young children to grow. Dwarf sunflowers are smaller than the regular tallest sunflowers, which can make them easier for young children to grow. They also make a great choice for gardeners with limited space or who want to grow flowers in containers. Most dwarf varieties grow between 6-40″ tall and produce bright yellow flowers in the summertime.
It’s possible to plant a container of dwarf sunflowers on your windowsill to create your own indoor window box.
- You can plant a container of dwarf sunflowers on your windowsill to create your own indoor window box.
- Sunflowers are easy to grow in a container, indoors or out. If you’re growing them in pots and planters, you’ll want to make sure those containers have drainage holes at the bottom, so that excess water doesn’t stay too long and cause root rot.
- The best time for planting dwarf sunflowers is after all danger of frost has passed and temperatures are above 40 degrees Fahrenheit (4 degrees Celsius).
Additional Different Varieties of Sunflowers You Can Grow
- Common Sunflower, Russian Mammoth (helianthus annuus)
- Perennial Maximilian Sunflower
- Swamp sunflower (helianthus angustifolius)
- Beach sunflower (helianthus debilis)
- Western sunflower (helianthus occidentalis)
- Mammoth gray stripe sunflower (helianthus annuus)
- Jerusalem Artichoke Sunflower (helianthus tuberosus)
Key Takeaways
The sunflower is a great addition to any garden! Growing them is fairly easy and quick, and they are great natural bird feeders. Sunflowers attract pollinators, create shade, and support soil health.
Are mammoth sunflowers perennials? No, but there are numerous native perennial sunflower varieties available. If you want a tall sunflower to fit into a small space, perhaps against a wall as a single plant, mammoth sunflowers might be a good choice. You can also choose to grow dwarf sunflower varieties to fill a smaller area in or around your house.
It is important that you take proper care of this plant when growing it so that you can enjoy it for many weeks to come and carefully harvest the seeds at the end of the growing season.