Growing giant sunflowers can be a challenge. But when you get it right there’s very few plants as iconic and fun as a massive sunflower.
Thankfully all it takes is the right techniques and a bit of patience. Do that and you can grow these impressive plants to their full potential.
So follow this step by step guide and it will help you to grow the tallest sunflowers and be the envy of all your neighbors.
Choosing the Right Variety
The first and arguably most important step is to choose the right variety of sunflower. These are some of the best choices:
- American Giant Known for reaching up to 16 feet tall with large 10 inch flowers. If you’re main motivation is height and a tall sunflower then this is the one for you.
- Mongolian Giant This variety can grow between 12 to 14 feet tall and has huge flower heads of 16 to 18 inches.
- Skyscraper Aptly named as it can reach heights of about 12 feet and can grow flowers that are up to 14 inches.
- Russian Giant This variety can grow up to 10 feet tall and produces very large 20 inch flowers.
You should think about the growing zone your in and length of your growing season when you choose which sunflower you’re going to go with. The varieties we’ve just gone through need a long growing period of around 70 to 120 days from the point you sowed them through to maturity.
Preparing the Soil
To thrive and grow at their best sunflowers need rich soil that drains well. You should prepare your garden ahead of time to get the best results. To do so:
Loosen the Soil
Start by loosening the soil to a depth of about 2 feet. Doing so lets the sunflowers taproots get into the soil easily. This helps in the long term as it keeps the sunflower stable and encourages strong growth.
Add Compost
Mix in 3 to 4 inches of compost so your sunflower gets the nutrients it needs. Compost can help to make the soil structure better, as well as adding beneficial microorganisms and holding on to moisture. Organic matter makes a big different to sunflowers.
Check pH Levels
Sunflowers prefer a slightly acidic to neutral pH. Somewhere between 6.0 and 7.5 is just right. Test your soil pH and adjust it if necessary by adding lime to raise the pH or sulfur to lower it.
Have Good Drainage
Good drainage is important as it stops waterlogging and this can end up with root rot. If your soil is heavy clay then add sand or organic matter as it will make the drainage better.
Sowing Seeds
Direct sowing is the best method for giant sunflowers because of the deep taproots. Follow these steps to sow your seeds:
Timing
Plant sunflower seeds directly in the ground after the last frost when night temperatures are consistently above 50°F.
This will usually be between late May and early June depending on what your climate is.
Spacing
Proper spacing is really important for giant sunflowers. They need space to grow. So plant yoir seeds about 1 inch deep and 6 to 8 inches apart at first.
If you’re planning to thin them later then plant your seeds closer together and then thin them to about 20 inches apart. Spacing like this will give each of your sunflowers enough room to grow their roots and grow tall without having to fight for the resources they need.
Watering
Give the soil a lot of water after you’ve planted the seeds to help them settle in. You’ll want to keep the soil moist until the seedlings emerge which should take about 7 to 10 days. Don’t overdo the watering though as too much will cause the seeds to rot.
Providing Adequate Sunlight
It won’t come as a huge shock that sunflowers love the sun (the name gives it away!). So they need a lot of sun to really thrive.
To make sure they get enough light follow these steps:
Full Sun Requirement
Sunflowers need at least 6 to 8 hours of direct sunlight each day. So pick a place to plant them that gets lots of sun all day. Uninterrupted sun is the best. South facing spots are usually best as they get the most sunlight throughout the day.
Avoid Shaded Areas
As they need so much sun you’re going to have to make sure your sunflowers aren’t in the shade. So look for buildings, trees etc. that could be overshadowing or casting some shade on to where you’re planting your sunflowers.
Not enough sunlight will stop your sunflowers from growing fully, give them weaker stems and make them more likely to be damaged from the rain and wind.
Consistency
Your sunflower will get to be as large as it can if it gets a consistent amount of sun. On cloudy or shaded days the growth may be slower but as long as it’s getting enough light overall it will still grow tall and strong.
Watering and Fertilizing
While not quite as important as sun, getting the watering and fertilizing right is still key to growing huge sunflowers.
Watering
- Initial Stage Keep the soil moist until the seedlings emerge. Watering fully will also encourage the roots to develop.
- Established Plants Once established sunflowers are relatively tolerant of drought. Water them well but don’t do it too often. During the hot weather you’ll want to up how often you’re watering but at the same time not let the soil get waterlogged.
- Avoid Overwatering Too much water can lead to root rot. Make sure the soil drains well so you don’t get standing water.
Fertilizing
- Organic Options Use a balanced, slow release granular fertilizer. Composted manure or fish emulsion are good choice for organic fertilizer. They will give your sunflower the nutrients it needs without the risk of over fertilization.
- Application Depth Work the fertilizer into the soil about 8 inches deep so that it reaches the roots. But don’t put the fertilizer directly on the seeds as this can damage them due to the salts in the fertilizer.
- Frequency Apply the fetilizer when you plant and then again when your sunflowers reach about 3 feet tall. This will give enough support for the bigger flowers and more rapid growth you’re looking for.
Thinning and Supporting
The right space and support are also important to growing big sunflowers. And because of their height you have to really make supporting them a priority.
Thinning
- Initial Thinning When the seedlings reach about 3 inches tall then thin them to the most vigorous ones, leaving about 20 inches between plants. This will reduce the competition for nutrients and sunlight, giving your sunflower the each to grow tall and strong.
- Gradual Thinning As plants grow thin them further if they’re taking up too much space. You want each of your sunflowers to have enough room to both develop it’s roots fully and to grow to it’s maximum potential.
Supporting
Giant sunflowers can become top heavy and may need support to prevent them from toppling over.
- Staking Use sturdy stakes placed about 1 foot away from the plant. As the sunflower grows tie it loosely to the stake using twine or garden ties and make sure you don’t damage the stem.
- Fence Support A fence can be a great natural support so if you can think about growing your sunflowers against or along one. Tie the stems to the fence with twine for extra stability.
- Wire Cages If you have planted a lot of ai flowers then putting a wire cage around them when they’re your can work well. The plants will grow through the cage and as they do the cage suppers them as they get taller.
- Trellises Putting sunflowers next to a trellis and tying the stems to it can also provide effective support.
Mulching and Pest Control
Mulching is important because it keeps the soil most and helps with controlling weeds. Pests can damage your sunflower so you have to keep them away.
Mulching
Apply 1 to 2 inches of compost or mulch around your sunflower. You can use finely chopped bark mulch as it works well.
Mulching will helps to keep moisture in the soil, suppress weeds and gradually decompose which will add nutrients to the soil.
Pest Control
Keep an eye out for common pests such as aphids, slugs and birds:
- Aphids Spray affected plants with a strong jet of water or use insecticidal soap to control aphids.
- Slugs and Snails Use barriers like crushed eggshells or diatomaceous earth to keep them away.
- Birds Netting will protect your sunflower heads from birds eating the seeds.
Common Problems
Even with the best care sunflowers can have some problems.
Diseases
- Fungal Diseases Sunflowers need good air flow. So space them properly. Try not to water from overhead either as this can lead to fungal infections like downy mildew and powdery mildew. If need be then fungicides can be used both to treat the problem or prevent it from occurring.
Stunted Growth
- Sunlight Make sure your sunflowers get at least 6 to 8 hours of direct sunlight daily.
- Spacing Any overcrowded plants should be thinned out so there’s enough space for them to grow.
Growing giant sunflowers isn’t particularly difficult. These tips are straightforward and should be easy enough to follow. And if you do then you’re giving yourself the best chance of growing huge and full sunflowers.
