Giant Sunflowers require consistent moisture, especially during their rapid growth phase. Water deeply at the base of the plant when the top 2-3 cm of soil feels dry. Avoid overhead watering to prevent fungal diseases.

Reduce watering slightly once flowering begins, but do not let the soil dry out completely.

Pruning is generally minimal for Helianthus giganteus. Remove spent flowers to encourage further blooming or to tidy the plant. Deadhead by cutting the stem back to a lateral leaf or the main stem.

Minimal structural pruning is needed as the plant grows upright naturally.

Propagate Giant Sunflowers from seeds sown directly outdoors after the last frost or started indoors a few weeks prior. Seeds germinate readily in warm soil.

You can also divide established clumps in spring, ensuring each division has at least one eye or bud. Handle roots gently.

Repotting is typically not applicable for Helianthus giganteus as it is a perennial usually grown from seed or divided from established clumps directly in the ground. If grown in a very large container for temporary display, repotting would occur when the plant becomes root-bound, usually into a significantly larger pot.