1. Choose the right seeds
Avoid traditional seed varieties and choose hybrid seeds that are developed to be consistent and always reliable. While older varieties often become top-heavy and fall over in wet or windy weather, hybrid varieties are selected to have strong, thick stems to support their heavy heads. Under ideal growing conditions, it can reach heights of 16 feet or more and produce large seed heads.
2. Preparing the land
Sunflowers need full sun; 6-8 hours of direct sunlight per day - the more the better if you want them to reach their full potential. Therefore, choose a shamba that is in direct sunlight and sheltered from wind.
Sunflowers thrive in warm to hot climates with full sun during the day. The dry season is perfect for growing sunflowers.
Check soil pH: Sunflowers prefer soil that is slightly acidic to slightly alkaline, with a pH between 6.0 and 7.5. Although they are relatively resilient and can grow in most types of soil.
Choose a well-drained site and start planting after the soil has fully warmed and the dry season has arrived.
Dig an area about 2-3 feet in circumference and about 2 feet deep and prepare the soil.
Sunflowers are heavy eaters and use up more soil than many other crops - especially if you grow them to a great height, so nutrient supplies must be replenished each season.
3. Sowing and thinning
For giant sunflowers with large seed heads, the ideal row spacing is 20 inches. If you plant them closer together, you may get taller stems but smaller heads. If planted farther apart, the seed heads may be larger but may be too heavy for the stems to bear.
To sow seeds, water the soil, then press the seeds 1 inch deep into 5-6 seeds, about 6-8 inches apart. If possible, cover loosely with netting to protect budding seedlings from birds. If the soil is kept moist, seedlings will appear within 5-10 days.
When the plants reach 3 inches tall, thin them down to 3 or 4 inches at their most vigorous. When they reach a foot tall, thin them to 2 inches and select the best, most vigorous candidates when they reach 2 feet tall. The purpose of this gradual thinning method is to ensure that you are left with at least one good seedling in the event that predators damage any other seedlings.
Remember, if you want to grow giant sunflowers, it's crucial to thin down to the best possible single seedling. Even a few seedlings growing too close together can prevent you from growing into a giant in your garden.
4. Feed and care for the growing giant
Feed frequently and water regularly. Although the plant is small, water it weekly at the root zone about 3-4 inches away from the plant, using about 2 gallons of a properly diluted liquid fertilizer solution each week. For larger plants, scrape a small donut-shaped moat about 18 inches around the plant and about 4 inches deep. Pour a few gallons of properly diluted fertilizer into the moat each week. Sunflower roots can grow up to 4 feet below the soil surface.
*Tip: Avoid pouring fertilizer directly onto the stems as this will cause them to rot.
Keep an eye on the weather forecast, especially as your plants become taller and more top-heavy. When strong winds are expected, delay watering to reduce the chance of being blown over. Staking is usually not necessary for sunflowers, but it can be helpful in windy areas or if they must grow in conditions that are too crowded or shaded.
Other tips:
- If you don't have a lot of space, it's better to plant fewer sunflowers because the more they are forced to compete for nutrients, the less viable each plant will be.
- Keep in mind that if you're not careful, sunflowers can grow very tall and may shade other plants. Sunflowers always point in the direction where the sun rises, so take this into consideration when planting.
- Soil type is not too much of an issue for sunflowers. Well-drained soil with plenty of peat, compost or manure will help them grow tall and strong
- Make sure there are no weeds around the sunflowers, and do not use chemicals or sow grass seeds near them.
Thanks to: Reene, Tom Heaton and Rob Craine