Mammoth Grey Stripe

Sunflower

90d to harvest

Mammoth Grey Stripe unfurls with a statuesque presence—heads that seem carved from dusk, their petals catching light in soft, smoky tones. The blooms carry bold, slate-edged striping that deepens as the season advances, offering a dramatic, long-lasting show in the garden while producing abundant seed for collectors and growers. Expect sturdy, upright plants with a commanding silhouette that thrives with steady sun and rewards with striking, gallery-worthy flowers.

Crop Dates

Growing note: In frost-free Zone 11a, grow this cool-season crop during the cooler dry season (October–February).

Milestone	Date
Start Indoors	—
Climate	Frost-Free Climate
Transplant / Sow Outdoors	Oct 1st
Harvest Begins	Dec 30th
Harvest Ends	Feb 28th

Crop Details

Trait	Value
Days to Maturity	90
Sun Requirements	Full Sun
Growth Habit	Upright
Support Needed	None
Planting Depth	Normal
Germination Temp (°F)	70
Min Soil Temp (°F)	55
Min Night Temp (°F)	40
Harden Off (days)	Not Required

Frequently Asked Questions

What’s the most common disease problem for Helianthus annuus (sunflowers) and how do I manage it?

Look for downy mildew or powdery mildew as white/gray fungal growth on leaves, especially after humid weather. Improve airflow by spacing plants properly, water at the base in the morning, and remove heavily infected leaves early; for repeat outbreaks, use a labeled fungicide compatible with food/ornamentals and follow the label schedule.

How often should I water Helianthus annuus during the main growing phase?

During active growth (roughly the first 6–8 weeks after emergence), keep soil evenly moist but not soggy—aim for deep watering about 1–2 times per week depending on heat and rainfall. Check by pushing a finger 2–3 inches into the soil; water when it’s dry at that depth, since sunflowers dislike constantly wet, cool soil.

How can I tell when Helianthus annuus ‘Mammoth Grey Stripe’ is ready to harvest?

Harvest when the back of the flower head turns yellow to tan and the outer petals start to fall, while the developing seeds in the head look plump and filled out. If you rub a seed gently with your thumb, it should feel firm and come off cleanly; most crops are ready around ~90 days from sowing.