Mammoth Grey Stripe

Family: Asteraceae Oilseed and ornamental annual

Planting Schedule

Provide your location or planting zone to unlock dates and add Mammoth Grey Stripe to a garden.

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.

Light: Full SunMaturity: 90 DaysHabit: Upright

Botanical illustration of Mammoth Grey Stripe

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Mammoth Grey Stripe Planting Dates by USDA Zone

Estimated US hardiness-zone windows for sow, transplant, and harvest. Enter a US ZIP above for exact local dates, or open a zone below.

Zone	Start Indoors	Sow / Transplant	Harvest
Zone 1a	Protected Environment Only
Zone 1b	Protected Environment Only
Zone 2a	Direct Sow	May 25th	Aug 23rd – Aug 29th
Zone 2b	Direct Sow	May 15th	Aug 13th – Aug 25th
Zone 3a	Direct Sow	May 15th	Aug 13th – Sep 1st
Zone 3b	Direct Sow	May 19th	Aug 17th – Sep 21st
Zone 4a	Direct Sow	May 15th	Aug 13th – Sep 24th
Zone 4b	Direct Sow	May 13th	Aug 11th – Sep 27th
Zone 5a	Direct Sow	May 8th	Aug 6th – Sep 30th
Zone 5b	Direct Sow	May 4th	Aug 2nd – Oct 5th
Zone 6a	Direct Sow	May 1st	Jul 30th – Oct 10th
Zone 6b	Direct Sow	Apr 25th	Jul 24th – Oct 16th
Zone 7a	Direct Sow	Apr 20th	Jul 19th – Oct 20th
Zone 7b	Direct Sow	Apr 10th	Jul 9th – Oct 28th
Zone 8a	Direct Sow	Apr 1st	Jun 30th – Nov 5th
Zone 8b	Direct Sow	Mar 23rd	Jun 21st – Nov 12th
Zone 9a	Direct Sow	Mar 6th	Jun 4th – Nov 26th
Zone 9b	Direct Sow	Feb 9th	May 10th – Dec 9th
Zone 10a	—	Oct 1st	Dec 30th – Feb 28th
Zone 10b	—	Oct 1st	Dec 30th – Feb 28th
Zone 11a	—	Oct 1st	Dec 30th – Feb 28th
Zone 11b	—	Oct 1st	Dec 30th – Feb 28th
Zone 12a	—	Oct 1st	Dec 30th – Feb 28th
Zone 12b	—	Oct 1st	Dec 30th – Feb 28th
Zone 13a	—	Oct 1st	Dec 30th – Feb 28th
Zone 13b	—	Oct 1st	Dec 30th – 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.