Glorious sunflowers bring happiness wherever they’re planted. If you’ve always wanted to add these yellow and majestic flowers to your garden but didn’t know how, the good news is that it isn’t difficult to grow them.
If you want to grow sunflowers indoors and outdoors, there are important steps to follow for your plants to thrive. These include choosing the right sunflower variety, planting your sunflowers from seeds, preparing the soil with the correct amendments, and choosing a sunny area for the plants.
In this article, I’ll look at all the essential tips you need to know about growing sunflowers, whether you want them indoors or in the garden. I’ll start with tips to help you grow sunflowers outdoors, followed by tips for growing them indoors in containers or pots.
How to Grow Sunflowers Outdoors
If you want to grow your sunflowers in the garden, the great thing about this is that you can choose tall sunflower varieties that add ornamental beauty to your home.
1. Choose Your Sunflower Variety
Before you plant the first sunflower seeds you find at your local nursery, it’s worth considering the sunflower varieties on offer. Some sunflower varieties grow to a height of 12 feet (3.7 m), and they display large flower heads. Others remain smaller, so they’re ideal for your home or floral arrangements.
With the above in mind, here are some sunflower varieties to consider:
As its name suggests, the American giant variety grows very tall. It can reach about 15 feet (5 m) in height! Its flower heads can grow to approximately 1 foot (30 cm) in width, so it’s the ideal flowering plant if you want to make a statement in your garden.
On the other side of the height spectrum is Little Becka, a dwarf sunflower variety. It grows to approximately 1-2 feet (30-60 cm) in height. What makes it special is that it has bright red and orange petals instead of the traditional yellow.
This sunforest mix variety grows to approximately 10-15 feet (3-4.6 m), and it’s ideal for creating a forest-like effect of sunflowers in your garden.
Schweinitz’s variety looks quite different from the sunflowers you might imagine. It’s a rare type of sunflower that can grow to a height of approximately 6 feet (1.8 m). It has narrow, lanceolate leaves and yellow flower heads.
2. Prepare the Soil for Planting
Although you might feel intimidated about growing sunflowers, especially in the garden, this doesn’t have to be scary. In fact, it’s quite easy to do, provided you have the correct planting site.
You should till the soil where you want to grow your sunflowers so that it’s soft and easy to work with. Tilling has other benefits, such as preventing the growth of weeds that will compete with your flowers for nutrients.
Plant Sunflowers in Healthy Soil
The great thing about sunflowers is that they’re not too fussy about the soil you plant them in. They perform well in soils that are a bit acidic or alkaline, so aim for a pH of 6.0 to 7.5. Luckily, this is an easy range to find.
If the pH of your soil is way outside the ideal range, you’ll have to make amendments to it. Amend the soil about 2 months before sowing the seeds since it takes a long time for most amendments to alter soil pH.
Here are some things to keep in mind:
- To lower the pH by 0.5, you can add elemental sulfur or aluminum sulfate to the soil. You can use no more than 2 pounds (0.9 kg) per 100 square feet (9.3 sqm). Adjust the amount in proportion to the size of your sunflower field or garden. Work the fertilizer into the top 6 inches (15 cm) of the soil.
- To raise the pH, you can add wood ash or finely ground lime. You can also use about the same amount of lime or wood ash in lieu of sulfur, but the rate at which they can raise the pH can vary depending on your soil type and composition.
The frequency of application can also vary based on your soil type. For instance, sandy soil can drop pH more quickly than clayey soil. The key is to check your soil pH regularly and take into account how slowly the amendments can alter the pH.
On the other hand, you can improve poor soil quality with some fertilizer, but choose slow-release granular fertilizer, and don’t give sunflowers too much nitrogen, as this can delay their blooming cycle. Something like a 6-10-8 NPK fertilizer will do fine.
Check Your Soil Drainage
If you have sandy soil that drains very quickly, it can benefit from organic matter like compost or mulch to enhance moisture retention. By comparison, clay soils hold too much water. Therefore, they need amendments, such as sand or perlite, to improve drainage.
The ideal type of soil for sunflowers is sandy loam soil. Organic matter is ideal for correcting soil that has a different texture from sandy loam.
You can use the regular compost you already have in your garden. This will ensure the soil can maintain a healthy balance of water and nutrients for your plants.
3. Grow Your Sunflowers From Seeds
Sunflowers are easy to grow from seeds, so check with your local nursery to see what sunflower varieties they have in stock.
Then, plant the seeds after the risk of the last frost has passed. The soil should have a minimum temperature of 60 °F (15.6 °C), so it’s ideal for planting sunflower seeds in the spring. However, you should plan to plant your sunflower seeds a few days after rainfall, as this will ensure the soil is soft.
Depending on the sunflower variety, your sunflowers will go from seed to bloom within 80-120 days.
Although soaking seeds before planting is sometimes recommended because it helps soften the coating of the seed to encourage germination, sunflower seeds don’t need to be soaked.
If you’d love a regular blooming cycle of your gorgeous sunflowers, a smart tip is to plant new rows of sunflower seeds every two weeks. This will keep your garden in bloom for longer.
4. Plant Them Directly Into the Ground
If you’re growing sunflowers outdoors, make sure you plant your seeds directly into the ground. This is because putting them in pots before transplanting them into the ground disrupts the plants’ long taproots. These roots grow very quickly and can experience stunted growth if confined to pots.
When planting your sunflowers, put them about 1 inch (2.5 cm) into the soil and space them about 6 inches (15 cm) away from each other. When setting up rows of sunflower seeds, put the rows about 20 inches (51 cm) apart. This encourages the growth of the plants and prevents them from being overcrowded.
This is the best distance to use when planting sunflowers because if you plant the seeds closer, the sunflowers that grow might have smaller heads and taller stalks. If you plant them further apart from each other, the heads might be bigger, but they could be too heavy for the stalk to hold up.
5. Provide Outdoor Sunflowers With Wind Protection
If you are growing sunflowers that can reach up to 10 feet (3 m) in height, make sure you plant them in an area of the garden that’s sheltered from the wind, such as along a fence or near a wall. This will protect the flowers from the wind so they won’t topple over during windy conditions.
You can also stabilize your tall sunflower plants using trellises or stakes to support their flowering heads.
Here’s how to stake your plants:
- When staking a tall sunflower, drive upright stakes into the ground.
- Fasten the plant to the stake with the use of twine.
- Adjust the twines as the plant grows taller.
Other tips to ensure that you properly stake your sunflowers include:
Staking Them Properly to Cut Them for Flowers Later
If you’re growing a group of sunflowers that you hope to cut for flowers, use a lattice of stakes and twine so that the sunflower plants will grow through the holes.
You should have two rows of staggered stakes with about 3 feet (0.9 m) of distance between the stakes. Use the twine to fasten the stakes.
Staking to Prevent Wilting
If you’re not interested in cutting your flowers later and just want the plants to grow healthy because they’re droopy, you should stake the individual sunflowers.
Put a stake about 3 inches (7.6 cm) from the stem of the plant. Fasten the stem to the stake with a bit of twine.
6. Give Them Enough Sunlight
Sunflowers are sun worshippers. They want to be planted in areas of the garden that get a lot of sun every day—between 6 and 8 hours of direct sun is required. Giving them as much time in the sun as possible will enable them to thrive.
“Direct sun” means that the sunlight touches the plant directly without being filtered, such as by a sheer curtain or the leaves of larger plants.
Sunflowers also require the correct temperature range to grow—they need between 70 and 77 °F (21-25 °C). They can tolerate high temperatures as long as you give them enough hydration.
7. Thin the Sunflower Seedlings
When the sunflower seeds germinate and sprout and seedlings start to grow, you should thin them if you want stronger plants that produce seeds. Wait for the plant’s second set of leaves to appear, then thin them so they’re approximately 2 feet (60 cm) apart.
However, if you’re growing sunflowers to later use in bouquets or other floral arrangements, don’t thin them. This ensures that the plants won’t grow too long, but they’ll have longer flowers and stems that look good in floral arrangements.
When thinning sunflowers, it can be useful to thin them gradually. This ensures you’ll have at least one seedling in case the others don’t survive. It will also enable you to enjoy the largest sunflower plant in your garden.
Here’s how to gradually thin your plants:
- Wait for the plants to grow to about 3 inches (7.6 cm) in height.
- Thin (or remove) the weaker plants or those that were planted too close together. This allows you to maintain the most vigorous plants.
- Let them grow to around 1 foot (30 cm), and thin them further to the most vigorous plants.
- When the plants reach about 2 feet (60 cm) in height, pull out the weaker plants, leaving behind only the healthiest plants.
8. Use Fertilizer to Enrich Poor Soil
If you have rich, loamy soil, you won’t need to feed your young sunflowers with fertilizer too often. This type of soil has everything your plants need to grow healthy. However, soil nutrients can be depleted over time, so you’ll need to add slow-release fertilizers once a year.
If your soil is too sandy and nutrient-deficient, you can supplement it with fertilizer. You can use a slow-release product that’s high in potassium and phosphorous. Avoid feeding your sunflowers too much fertilizer, though, as this can cause them to become thin and spindly.
9. Water Your Sunflowers When Their Soil Is Dry
Sunflowers can tolerate dry conditions, but you want to stick to a regular watering schedule to encourage them to flower. If sunflowers don’t get enough water, such as in a drought, they won’t produce many flowers.
A good tip to follow when watering sunflowers is to let the top 2-3 inches (5-7.6 cm) of soil dry out between waterings. Check your plants for signs that they’re not getting enough water. For example, if they’re starting to look droopy.
Once your sunflowers have started to grow, they should be watered with 1 inch (2.5 cm) of water per week. A good way to ensure you don’t overwater them is to use a watering nozzle.
When you water your sunflowers, ensure that the top 6 inches (15 cm) of their soil is moist afterward, as this indicates they’ve been watered thoroughly.
If you’re a visual learner, I recommend watching my YouTube video on how long sunflowers last without water. I’ll walk you through the amounts of water sunflowers need at different growth stages. So definitely give the video a watch if you want to learn more about the watering needs of sunflowers.
10. Protect Your Sunflowers From Common Pests
Once your sunflowers start to grow, you will need to protect them against various animals that are drawn to them, such as squirrels, birds, and deer. Generally, seedlings can be protected by mesh wastebaskets that will encourage air circulation and light for the seedlings and prevent the animals from digging up the seeds.
To protect your sunflowers from squirrels specifically, start your sunflowers indoors a few weeks before the last expected frost, as this will prevent rodents from digging up your plants. They do this because they want their seeds.
When the plants grow to about 6 inches (15 cm) in height, they won’t hold the same appeal for animals and will be protected against their damage.
You can also place chicken wire or wire mesh around your sunflower seedlings to keep pests like squirrels away. It will also keep other animals, such as rabbits, away from your plants.
Birds are problematic because they damage gorgeous plants by eating sunflower heads. To keep them away from your sunflower site, consider placing a scarecrow to frighten them. An alternative is to place a reflective hanging ornament on a nearby tree.
For deer who like to eat the leaves and flowers on your sunflower plants, a tall fence that’s approximately 8 feet (1.8 m) in height will work well to prevent them from gaining access to your prized plants.
11. Be Careful When Planting Companion Plants
When choosing what plants to grow within close proximity to your sunflowers, you must be careful. Sunflower seeds contain allelopathic chemicals.
These are said to inhibit the growth of other plants, including weeds. Potatoes and beans are two plants that are especially damaged by this chemical, so never plant them close to your sunflowers.
You also need to be careful if you’re tilling your sunflower remains at the end of the season to reuse them in a veggie patch, as they can still harm the potatoes and beans that you’re planting there.
12. Collect Your Sunflower Seeds
When the sunflower plant’s blooms start to drop, you can collect the plant’s seeds to grow new sunflowers in your garden.
Here’s how to collect the seeds from the plant:
- Cut the flowers, ensuring they have a long stem.
- Cover the flowerheads to protect them from birds. You can do this by putting a paper bag over them.
- Leave the flowers somewhere dry and warm with good ventilation so that they dry out. This could take a few weeks.
- When the seeds are dry, you can remove them from the sunflower heads by hand.
- Store the seeds in an airtight plastic container.
- Keep the seeds in a cool, dry area of the home until you’re ready to plant them.
If you want to learn more about how sunflowers grow and produce seeds, the best varieties to keep in your garden, and how to grow and care for them correctly, check out my other article: Do Sunflowers Need to Be Pollinated to Produce Seeds?
13. Propagate Sunflowers From Cuttings
Instead of planting seeds, you can also propagate your sunflowers from cuttings. Make sure you take them before the peak of the season’s growth.
- Use a sharp knife to cut a 4-inch (10 cm) stem from the sunflower plant. Ensure it doesn’t have any buds or flowers on it.
- Cut away the lowest leaves of the stem so that you can see the node.
- Cut away the top 1/2-inch (1.27 cm) of the cutting, leaving two leaves.
- Apply rooting hormone to the cutting end.
- Plant the sunflower cutting in a peat moss and sand mix. The stem section containing no leaves should be planted into the medium.
- Cover the sunflower cutting with a plastic bag. Check on it regularly for roots, which should start to grow within 2-4 weeks.
- When you’re ready to plant the cutting, keep it in light shade for a week before planting it in a sunny garden area.
14. Protect Sunflowers During Winter
If winter in your region doesn’t provide a lot of sun, your sunflowers could produce fewer flowers. Most sunflowers are annual plants. They germinate late in the spring, flower in the summer, and then die when the first frost of fall occurs.
In the winter, your sunflowers will drop their seeds and die. If you own a perennial sunflower plant, you can let this process happen naturally so that you enjoy your pretty sunflowers the following year.
But to keep your perennial plants alive during the fall and winter, you should apply 2 inches (5 cm) of mulch around them. Do this during fall after the first frost has killed back the sunflowers.
Remove any dead leaves on the plant before you apply the mulch. Mulch will keep your sunflower plants alive during winter because it insulates the soil when temperatures drop.
How to Grow Sunflowers Indoors
One benefit of growing sunflowers indoors is that you don’t have to worry about animals attacking your plants for their seeds.
However, there are some important tips to keep in mind so that your indoor sunflowers bloom beautifully in your home:
1. Choose a Smaller Sunflower Variety
It’s not feasible to grow very tall sunflower plants in your home, so ensure you plant a variety that will remain small.
Examples of sunflowers that you can grow indoors with success include the following types:
This sunflower plant reaches 1 foot (30 cm) in height. It blooms in yellow and orange petals. Its flowers don’t have individual petals but rather a fuzzy mass of tight petals, giving it an unusual and eye-catching appearance.
Jade is a dwarf sunflower variety that reaches up to 4 feet (1.2 m) in height. You’ll love that it grows quickly. It has petals with a slight green tinge of color, hence its name, making it quite unusual.
The Dwarf Pacino sunflower will grow to about 10 inches (25 cm) in height. Its flowers have bright yellow petals with striking dark centers.
2. Choose the Right Container
If you have a small sunflower variety, you should grow it in a 2-gallon (7.6 liters) container. Larger varieties should be planted in 5-gallon (19 liters) containers. Ensure that the container or pot in which you grow indoor sunflowers is between 12 to 18 inches (30-46 cm) in depth.
The container needs drainage holes to prevent sunflower roots from sitting in water, which can lead to issues such as root rot.
You can also make your own drainage holes in your pot or container with a drill and a 1/2-inch (1.27cm) drill bit. If you don’t have a drill, you can punch holes with a hammer or a nail.
Learn more about how to put holes in plastic pots without a drill in my article here. How To Put Holes in Plastic Pots Without a Drill
3. Plant Sunflower Seeds 1 Inch (2.5 cm) Into the Soil
Once you’ve planted the sunflower seeds in your pot, ensure they are about 1 inch (2.5 cm) deep into the soil. They also require about 4 inches (10 cm) around all sides of the seed. This is important so that the sunflower roots have enough space to grow.
You should avoid planting the seeds too close to the sides of your pot or container.
4. Plant Sunflowers in Well-Draining Potting Mix
Another thing you should do to ensure your indoor sunflowers don’t sit in wet soil is to plant them in a well-draining potting mix.
You can enhance the drainage of your sunflower plants by adding 25% perlite or pumice to your regular potting soil. This will encourage water to drain instead of making the medium too soggy.
5. Plant Seeds in Peat Pots to Transplant Sunflowers Later
Earlier, I mentioned how important it is to plant sunflowers into the ground directly instead of transferring them to your garden later, so you don’t disturb their roots. However, if you’re growing plants indoors, you can use peat pots.
These pots are great for planting because when you’re ready to plant the flowers in your garden or a larger pot, you can simply plant the entire pot, and it will break down in the soil. This prevents damage from being caused to the plant roots during transplantation.
When planting your sunflower seeds in these pots, you should plant 3 seeds per 4-inch (10 cm) pot. This prevents overcrowding. Once you’ve planted the seeds, they should germinate within 6-10 days.
Pro tip: Encourage the indoor sunflowers to bloom throughout summer by planting seeds every few weeks. This enables you to fill your home with stunning sunflowers until fall.
6. Thin the Indoor Seedlings to One Sunflower per Pot
When your sunflower seedlings grow their first true leaves, you should thin them. This will ensure that you focus on growing the strongest plants that will thrive.
Small sunflower varieties require about 6 inches (15 cm) between plants to ensure they have enough room to grow. If your plants are overcrowded, they will struggle to thrive. This will cause them to have shorter stems and smaller blooms.
Try to thin your seedlings so you’re left with one seedling per pot or container.
7. Water Your Indoor Sunflowers Thoroughly
Newly planted sunflower seeds will require more water to help them germinate. Water them immediately after planting them in pots, then keep the soil moist. You should continue to water them until they germinate lightly.
To increase their moisture, you can cover the pots with clear plastic wrap. This will lock in humidity and moisture. However, remove the plastic once the seeds have sprouted.
It’s easy to fall back on watering your established indoor sunflowers, but sunflowers grown indoors can dry out much faster than sunflowers planted in the ground. This is why you must keep an eye on your sunflower’s moisture.
A good rule to follow is to stick to watering your indoor sunflowers every 5-10 days once they’ve germinated. Then, keep the soil adequately moist by watering your plant as soon as the top 2-3 inches (5-7.6 cm) dry out.
It’s recommended that you place a tray underneath your sunflower container or pot. After soaking the pot with water, ensure you can see the water exit the drainage holes. This is a good indication that you’ve watered your sunflower enough.
8. Place Sunflowers in an East- or South-Facing Window
You need to place your sunflower pot in an area of the home where it will get at least 6 hours of sunlight every day. This should be an area of the home that’s in front of an east- or south-facing window.
If you don’t get enough full sun in the home, such as during winter, consider placing your sunflowers on a sunny balcony or patio. Alternatively, use fluorescent full-spectrum lights. Note that sunflowers grown under fluorescent lights won’t bloom as well as those that receive natural light.
Without enough light every day, the sunflowers won’t bloom as much, so you want to avoid depriving them of light. Sunny conditions aside, you should also keep the sunflowers in a warm location where the soil is around 60 °F (15.6 °C).
Rotate the Sunflower Pots
Sunflowers are heliotropic, which means they turn toward the light. You should ensure they get enough light on their parts by regularly turning their pot. This prevents the sunflower seedlings from bending over, drooping, or becoming leggy as they try to stretch for the light.
Remember to turn your plants, especially if you have many in the home, and stick to the rule of rotating the pots a quarter turn every time you water them.
If your seedlings become leggy, they may still be salvageable. Some people prefer to bury leggy sunflower seedlings to make them grow again. Read my blog post to see if it’s possible: Can You Bury Leggy Sunflower Seedlings?
9. Fertilize the Indoor Sunflowers
Since your sunflowers growing indoors won’t have the same soil-based nutrients they’d get if they were planted outside, you have to feed them fertilizer.
Two types of fertilizer are ideal to use on indoor sunflowers, as we mentioned earlier in this article:
- A high-nitrogen liquid fertilizer boosts the sunflower’s growth when applied only once in the early stages.
- Before the plant flowers, you should use a liquid fertilizer that’s rich in phosphorus instead. Always use liquid fertilizers at half-strength.
10. Harden off Your Seedlings When Moving Them Outside
If you’re going to move your indoor sunflower seedlings into the garden at a later stage, you’ll need to harden off the seedlings beforehand. You should do this when they start to grow two sets of leaves.
Hardening off is a process involving acclimatizing the plants to the outdoor environment.
To do it correctly, keep your pots outside when the weather is warm and then bring them back inside at night so that they don’t get damaged by the cold. You should do this for a few days so that the plant gets used to the conditions before being planted in the soil.
You should plant your sunflower seeds in the garden after the last frost in your area. This ensures that they’ll get a good start outside.
11. Check for Problems With Mold
Although your indoor sunflowers won’t be a target for typical garden pests such as rabbits and deer, they can become targets for mold.
Here are two to look for so that you can treat them quickly and make your sunflowers healthy and beautiful again:
If your sunflower is placed in a moist, cool environment, white mold will be attracted to it.
White mold attacks the roots of the plant and displays symptoms such as:
- Dark stem cankers
- Stem wilt
- Leaf wilt
If these symptoms are ignored, they’ll get worse. You’ll see wet, gray lesions on the stalks that are covered in fungal strands, and the flowerheads will start to rot.
To prevent this mold from affecting your sunflower plants indoors, make sure you avoid exposing them to these conditions:
- High levels of humidity (Indoor humidity levels of 30% or less with good air circulation is acceptable)
- Temperatures that are consistently below 60 °F (15.6 °C)
- High-nitrogen fertilizer
- Overcrowding in pots
Unfortunately, you’ll have to remove plants that have been infected with this mold early on and remember to remove all their soil, too, as this can spread the disease to other plants.
If you’re wondering why your indoor sunflowers aren’t opening, or the mature flowers on the plant are becoming discolored, the culprit could be gray mold. It occurs when there’s a lot of humidity.
To treat flowers affected by gray mold, you should remove all the leaves and flowers that are affected by silvery-colored spores.
To prevent it from occurring in the future, follow these good practices:
- Never water your sunflowers from above, as this causes water to splash over the stems and foliage.
- Avoid overcrowding your sunflowers. Ensure good circulation between plants.
Growing sunflowers, indoors or outdoors, doesn’t have to feel intimidating.
These gorgeous flowers can thrive as long as you follow some simple tips to keep them healthy, such as:
- Giving them at least 6 hours of sunlight every day
- Letting the top 2-3 inches (5-7.6 cm) of their soil dry out between waterings
- Planting them indoors in peat pots, so they’re easy to transplant into the garden
- Using stakes to support them if you’re growing a tall sunflower variety