Sunflowers are strong and hardy flowers that can survive in almost any type of soil. They will grow even in poor soil conditions, however, they will not grow as large. To produce the healthiest sunflowers, they need to receive the proper nutrients.
One of the main nutrients that sunflowers need is water. To survive and reach a good height, sunflowers must have enough water so as not to wilt. Because of this some might tend to over-water sunflowers. This can weaken the soil and cause the flowers so lean or fall over. Just make sure the soil is damp, and if it rains, avoid watering for a day or so until the rain water has been absorbed.
Sunflowers, like their name implies, need a fair amount of sunlight. Planting in full shade will result in limited to no growth. Sunflowers should receive around eight hours of light per day.
Sunflowers will grow in all kinds of soil. However, proper nitrogen and phosphate levels in the soil will insure optimum growth. A soil test can determine if these levels are appropriate. In the absence of a test, a slow-release fertilizer can be used in early spring before new growth emerges.