Fast Facts
About Mammoth Sunflower
Mammoth sunflowers grow tall stems and oversized golden flower heads that make a striking garden backdrop. Direct sow after frost in a sunny spot with enough room for the mature stems.
When to Plant Mammoth Sunflower Seeds
Direct sow outdoors after frost when soil has warmed. These large plants perform best when they can grow in place from the start.
Where to Plant Mammoth Sunflower Seeds
Provide full sun, deep well-drained soil, and room for a tall mature stem. Avoid a narrow container that will restrict roots.
How to Plant Mammoth Sunflower Seeds
Prepare a weed-free bed and loosen soil deeply.
Sow about 1/2 to 1 inch deep, following the packet for exact depth.
Thin to approximately 12 to 18 inches apart, or to the supplier spacing for your strain.
A commonly listed sowing depth for this type is 1/2 inch; verify against the supplied seed lot; check the actual packet before sowing. Use the packet to confirm final spacing; a general reference is 12 to 18 inches; verify against the supplied seed lot.
How to Harvest Mammoth Sunflower
Leave the large head to mature if seed is the goal. Once the back turns dry and the seeds are fully formed, cut the head and finish drying it in a ventilated place. For flowers, cut before the head is fully open.
How to Care for Mammoth Sunflower
Water deeply while roots establish and during long dry periods. Stake only if the site is exposed or stems become unstable. Protect young seedlings from browsing.
Companion Plants
Use as a tall backdrop behind lower zinnias and marigolds.
Related Planting Guides
Growing details can vary by seed lot and climate. Mammoth strains differ; final height and head size are not guaranteed. University extension gardening resources