Seeds – Sunflower, Mammoth OG (HM) High Mowing

Latin Name: Helianthus annuus
Main Uses: Culinary, Ornamental

Zone Hardiness: 110 days
Exposure: Full sun
Height: 12′
Flower Color: Yellow
Certified Organic: USDA Certified Organic

Germination: 7 – 14 days at 21°C.
Indoors: Sow sunflowers indoors 2 – 4 weeks before the average last frost date to get a head start on flowering. Sow 2-3 seeds direct to a minimum 7.5 cm (3″) pot and use containers that are biodegradable and can be planted into the soil outdoors. Thin to strongest seedling when plants are 15 cm (6″) tall.

We recommend applying a kelp supplement such as Sea Magic starting at the time of sowing, then weekly through the growing season. A transplant fertilizer such as Evolve Seedling starter can be alternated with the kelp on a bi-weekly basis once the second set of true leaves have emerged.

Outdoors: It is easy to start sunflowers direct to the garden or large pots outdoors, but this does delay flowering by a few weeks compared to those started inside. However, direct-seeded sunflowers generally grow taller than those transplanted from pots (due to damage to roots when growing in starter containers).

If direct seeding outdoors, waits until the soil has warmed in the first week of June. Sow in rows, planting small clusters of 5 seeds approximately every 15 cm (6″). As the seedlings grow up, gradually thin them down to one strong plant spaced every 30 – 50 cm (12 – 20″); do a first thinning when plants are about 30 cm (12″) tall, then a second when they get to 60 cm (24″) tall.  
Planting depth: 2.25 cm (1″) deep. Cover lightly with soil.

Growing in Containers: Sunflowers can be grown in extra-large planters but will be stunted in smaller ones. If growing in containers, feed sunflowers weekly with a higher nitrogen organic fertilizer such as Evolve Fish Grow, as they are heavy feeders. 

Growing in Mixed Planters: Not suited for mixed planters, except for large landscape pots or raised beds. Be mindful that sunflowers are very domineering plants and develop large roots that will soak water and nutrients away from other plants in mixed containers.

Fertilizing (Garden): Sunflowers thrive on rich soil, so be sure to amend garden beds amply with quality compost ahead of planting. We recommend Sea Soil. If large plants and seed heads are desired, feed sunflower weekly with a liquid organic fertilizer such as Evolve Fish Grow. 

Watering (Garden): Water regularly to establish. Once mature, water deeply, soaking the roots at least once per week (although excessive moisture can cause stem root, so champion sunflower growers will dig a little ring moat about 30 – 60 cm (12 – 24″) out from the stem, and water there. 

Beneficials Attracted to this Plant: Birds will love feeding on the seed heads in fall (and winter, if left standing).

Harvesting: Heads can be harvested as soon as the back of the flowers start to turn from green to yellow. Cut plants to 1 foot, place heads on screened drying racks, in paper bags, or other clean location to capture mature seed. Choose a well-ventilated location out of direct sunlight for drying. When seeds are ripe they simply fall from the heads.

Suitability for Indoors: Not suited for indoors.