Russian Mammoth Sunflower, Heirloom, 9-12-foot Tender Reseeding Annual. This classic sunflower was first offered in the 1880"s. Still widely prized for its gigantic flowers and abundant, nutritious seed. Planting Depth: 1-inch , Soil Temp. for Germ: 60-70-Degree F, day to Germ. 6-12, Plant Spacing: 1-2-inch , day to Maturity: 110, Full Sun, Water Less, Drought Tolerant, 25 Seed Count.