1.Choosing the right seeds

Avoid the traditional variety of seeds and get yourself Hybrid seeds which are developed to be uniform and consistently reliable. While older varieties often become top-heavy and fall over in wet or windy weather, Hybrids have been selected for a strong, thick stalk to support its heavy head. In ideal growing conditions, it reaches heights of 16 feet or more and produces huge seedheads.

2. Soil Preparation

Sunflowers need full sun; see 6-8 hours of direct sunlight per day – the more the better if you are trying to grow them to their maximum potential. so get a shamba where there is direct Sunlight and sheltered form wind.

Sunflowers thrive in warm to hot climates with full sunshine during the day. Dry seasons are perfect for growing sunflowers.

Check Soil PH: Sunflowers prefer a slightly acidic to somewhat alkaline soil with a pH between 6.0 and 7.5. even though they are  relatively resilient and can grow in most types of soil.

Choose a well-drained location, begin planting after the soil has completely warmed and the dry season has set in.

Prepare your soil by digging an area of about 2-3 feet in circumference to a depth of about 2 feet.

Sunflowers are heavy feeders and deplete the soil more than many other crops – especially if you are growing them to reach a massive height so the nutrient supply must be replenished each season.

3. Sowing and Thinning

The ideal spacing in rows for giant sunflowers with large seed heads is 20 in. apart. If you plant closer, you might get taller stalks but smaller heads. If you plant farther apart, the seed head may be larger, but possibly too heavy for the stalk to bear.

To sow seeds, water your soil, and press seeds 1 inch deep in clumps of 5-6 seeds about 6-8 in. apart. If possible, cover loosely with netting to protect emerging seedlings from birds. If the soil is kept moist, seedlings will appear within 5-10 days.

When the plants grow to 3 inches, thin them to the most vigorous 3 or 4. When they are a foot tall, thin them to 2, and when they reach 2 feet high, select the best, most vigorous candidate. The point of this gradual thinning method is to ensure that you’re left with at least one good seedling in the event that predators damage any of the others.

Remember, it’s critical to thin back to the best single seedling if you’re going for giant sunflowers. Leaving even several seedlings growing too close together will keep you from growing a giant in your garden.

4. Feeding and Care of Your Growing Giant

Feed often and water regularly. While the plant is small, water around the root zone, about 3-4 in. from the plant with about 2 gallons of properly diluted liquid fertilizer solution per week. For larger plants, scrape out a small doughnut-shaped moat about 18 inches around the plant and about four inches deep. Pour several gallons of properly diluted fertilizer into the moat every week.  Sunflower roots can grow to 4 feet below the soil surface.

*tip: Avoid pouring fertilizer directly on the stems, since this can cause them to rot.

Be attentive to weather reports, especially, as your plants become taller and more top-heavy. When heavy winds are predicted, delay watering to reduce their chances of blowing over. Staking isn’t usually necessary for sunflowers, but it can be helpful in extremely windy areas or if they must be grown in conditions that are too crowded or in too much shade.

Other Tips:

• It is better to plant fewer sunflowers if you don’t have much room because the more they are forced to compete for nutrients, the less strong each individual plant will be.
• Remember that sunflowers will grow very tall and can shade out other plants if you are not careful. Sunflowers always point to the direction that the sun rises, so consider this when planting.
• Soil types are not too much of a problem for sunflowers. Well-drained soil with lots of peat, compost, or manure will help them to grow tall and strong
• Keep the area around the sunflowers weed free, and do not use chemicals or sow grass seeds near them.
  

Thanks to: Reene,Tom Heaton and Rob Craine