Mammoth Sunflower
Helianthus annuus 'Mammoth'
flowerThe iconic tall annual sunflower producing massive seed-filled heads 12 to 18 inches across on 8 to 12-foot stalks. Edible seeds are high in protein and healthy fats. Flowers track the sun when young (heliotropism) before becoming fixed east-facing at maturity. One of the most productive and dramatic plants in any garden, attracting goldfinches, bees, and countless beneficial insects.
☀️
Sun
full sun
💧
Water
Every 3 days
🌸
Bloom
~90 days
📊
Difficulty
easy
🌱
Lifecycle
annual
One season, then done
↔️
Spacing
24-36 in
⬇️
Planting Depth
1 in
🧪
Soil pH
6.0-7.5
Growing Details
Soil Type
Well-drained
Hardiness Zones
Zones 4 – 11
Grown as an annual — this range is its winter hardiness, but you can grow it for a single season in any zone.
When to Fertilize
At planting with balanced fertilizer; one phosphorus-rich side-dress at bud stage
Fertilizer
Balanced 10-10-10 at planting; avoid high nitrogen which causes excessive leafy growth; phosphorus boosts head size
🌱 Growing Guide
Direct sow after last frost when soil reaches 60 F. Sunflowers resent root disturbance and are best direct-sown. Plant in full sun in a sheltered spot — tall plants can snap in high winds. Stake if needed once plants exceed 5 feet. Water deeply but infrequently; sunflowers are surprisingly drought-tolerant once established. For the largest seed heads, grow one plant per location and thin ruthlessly.
🌼 Have a different variety?Cultivars of the same species usually share the same basic care — they differ mainly in flower color, height, and bloom form, not in how you grow them. So this guide still applies even if your exact variety isn't the one shown.
Planting Calendar
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Direct sow
Apr 29
🌸
Projected first bloom
Jul 28
JJan
FFeb
MMar
AApr
MMay
JJun
JJul
AAug
SSep
OOct
NNov
DDec
✅ Plant alongside
Good neighbors that attract beneficial insects or deter pests
- Cucumber — Sunflower provides trellis and shade; attracts pollinators for cucumber fruit set
- Corn — Sunflower attracts pest-eating birds and insects that also protect corn
- Most vegetables — Outstanding pollinator attractor; beneficial insect habitat throughout the garden
- Squash — Tall sunflower creates a windbreak and provides habitat for beneficial predators
❌ Keep away from
PotatoesPole Beans
🛡️ Pest & disease prevention
Proactive ways to stop trouble before it starts — tap a name with an arrow for its full guide
Row cover on seedlings; Bt spray if severe; handpick adults
Sunflowers often attract large aphid colonies on stem tips — this is beneficial as it draws ladybugs and lacewings to the garden; remove only if overwhelming
Ensure airflow; avoid overhead watering; resistant varieties available
Wrap maturing seed heads in paper bags or netting; or accept and enjoy the goldfinch activity
🌸 Blooms & cutting
For fresh flower arrangements: cut when the outermost ring of petals is just opening. Vase life 5 to 10 days. For seeds: wait until the back of the head turns brown and papery and the seeds appear plump and striped. Cut with 12 inches of stem and hang in a paper bag in a dry place for 2 weeks. Rub seeds out with your hand. Roast at 300 F for 30 to 40 minutes for snacking.
🥗 Nutrition & benefits
As a companion plant: one of the best garden plants for supporting bird biodiversity. Seeds are among the highest in linoleic acid (omega-6) and vitamin E of any food. Attracts more bee species than almost any other garden annual. Seed heads support goldfinches, chickadees, and nuthatches well into winter.
For educational and informational purposes only — HomeSown is not medical, health, or other professional advice. Always positively identify any plant before handling or eating it; some plants, and some parts of otherwise-edible plants, are toxic. Consult a qualified professional before consuming or otherwise using any plant, especially if you are pregnant, nursing, taking medication, or have a health condition.