Giant Sunflowers need to be grown in full sun. Soil conditions can vary, from average a to rich soil. To produce optimum growth, the soil should be very rich. The richer the soil, the better the plant growth. The soil should also be well drained. Dig a hole two to three feet deep. Fill it with layers of compost, regular garden soil, and manure. This will help to promote optimum plant growth.
One of the important ingredients to fueling giant growth, is a regular supply of fertilizer. Begin your fertilizer regimen with a high nitrogen formula. If you are growing sunflowers for record height, continue the high nitrogen formula all season long. For big blooms, switch to a high phosphorous formula, as the plant nears its expected height and the flower head begins to form.
Give your plants a regular supply of water. Deeply water your plants, to assure it gets to all of the roots. Do not allow the soil to dry out. And, do not soak the soil.
Staking giant sunflower plants is very important. These tall, heavy plants are susceptible to falling over on windy days. The stake doesn’t have to be as tall as the plant. But, it should be several feet tall, and anchored firmly into the ground.
Harvest sunflower seeds after the bloom has dies. Check a seed or two. Squeeze it to see if it is hard and full. If hollow or soft, it is not ready. The trick is to get them when they are mature, and before the birds get to the seeds.