The Mammoth Grey Stripe Sunflower produces a single yellow bloom ranging from 25-35 cm (10-14″) in diameter. Grey Stripe Sunflowers grow on tree trunk like stems and can easily grow to 3-3.6 m (9-12’) in height! The flower heads are surprisingly heavy, laden with large grey striped seeds. Seeds can be used for fresh sprouts since they’re huge. Sunflower seeds are a popular protein-rich food, and are very popular with the birds and bees find them irresistible.
Sow under glass March-April and outdoors April-June after your last frost for flowers July-September.
Direct sow seeds in mid-April to late May. Select a well-drained location that receives lots of sunlight and sow seeds after your last frost. Starting seeds indoors is possible, but does not gain much time. Better to directly sow seeds in a final location to allow for better root development. Sow seeds 2.5cm (1”) deep, space dwarf varieties at least 15cm (6″) apart and the larger varieties at least .6m - 1m (2-3’) feet apart. Warmer soils will promote faster germination. The optimal soil temperature for germination should be around: 21-30°C (70-85°F). Seeds should sprout in 10-21 days. Keep soil moist, but not soggy while awaiting germination. Moderate watering will suffice once seedlings break through the soil. Select a well-drained location that receives lots of sunlight after the last frost to transplant from pots.
Soil Conditions: Well worked rich, loose well-drained soil. Soil PH: 5.5-7.0, Ideal 6.3-6.5
Planting Depth: Sow seeds 2.5cm (1”) deep.
Germination: 10-21 days.
Height at Maturity: 3-3.6 m (9-12’) tall.
Days to Maturity: 100 days. When the back of the flower head turns a ruddy yellow to brown, it is ready to be cut from the plant.
Watering: Keep watering schedule consistent throughout the season. The average sunflower uses 3-4mm (0.15”) of water daily during active growth. Sunflowers are drought tolerant, but grow better if you provide them with regular water, especially 20 days before they flower and 20 days after they flower.
Sun/Shade: Full Sun
Spacing after Thinning: Space dwarf varieties 15cm (6″) apart. Giant varieties 1m (3′) apart.
Additional Information Harvesting of annual sunflowers should not begin until the petals wilt and begin to fall off the flower head. You can prevent seed loss from local critters like birds, deer and squirrels by covering the flower heads with paper bags and tying the bags closed. After the seed shells fatten up but before they dry out, cut the sunflower stalks about 30-45 cm (12-18”) below the flower. It's best to tie the flower head stalks together and hang them upside-down in a dark place at room temperature. Some flower heads will be surprisingly heavy – so use a heavier type cord or rope. Using a fan will ensure good air movement and promote better drying conditions. After the shells dry for a month or so, remove the seeds by rubbing two heads together.