The care information provided in this section represents the kind of practical advice is available for all the plants in this web site if you subscribe to the monthly customized newsletter Yardener’s Advisor.
Because sunflower roots spread widely, the plants can withstand some drought. However, it is best to water them regularly during their most important growth period, about 20 days before and after flowering. If you have good soil with lots of organic matter and if your sunflowers are well mulched, you will need to water them only if it has not rained for a week or two.
If you have poor soil with little organic content or if you choose not to use mulch, then you may have to water almost every sunny day. Deep, regular watering helps encourage root growth, which is especially helpful with taller sunflower varieties bearing top-heavy blooms.
Sunflowers do not require a rich diet. If you have soil with lots of organic matter, the earthworms and microbes in that healthy soil provide the necessary nutrients in most cases. However, because sunflowers grow vigorously (they can grow 6 feet in just 3 months), it’s a good idea to add some slow-acting granular fertilizer to poor, thin soil.
The better their diet, the larger the sunflowers. Do not overdo the nitrogen, because that will delay flowering. However, to grow super sized seed heads fertilize a bit extra when they first appear and start to develop.
Although sunflowers can get by without much attention to their soil, spreading a mulch layer of some kind of organic material on it provides several benefits. Mulch reduces soil moisture loss through evaporation, discourages weeds, and cools the soil. Best of all, the organic matter gradually decomposes and improves the soil.
After the plants have sprouted, spread about 2 inches of straw, chopped leaves, wood chips, or shredded bark on the soil. Use peat moss only if it is mixed with some other organic material. Used alone, it tends to crust over and repel water. For more information see the file on Using Mulch
While a few sunflower varieties do not need any staking, it is a good idea to support plants that grow over 3 feet tall or are multi-branched. Their branches are fairly brittle, especially at the points where they join the stems. Shallow rooted and weighed down with many large flower heads, they are vulnerable to summer winds and rain as well as passing yard care equipment. Tie the plants loosely to stakes with lengths of cloth or other soft material as needed.