Granddaddy Purple
Cannabis seeds
by Royal Queen Seeds
Granddaddy Purple Autoflower Seeds by Royal Queen Seeds
Granddaddy Purple Autoflower is a fast-finishing indica-dominant cannabis seed that delivers heavy purple buds in just 12 weeks from germination. Royal Queen Seeds crossed Purple Urkle with Big Bud Auto to create a compact, fuss-free plant that produces dense flowers with up to 19% THC — no light schedule changes needed. If you want that classic GDP berry aroma without a complicated grow setup, this is the seed to pop.
Pack Sizes
| Pack | Seeds | Best for |
|---|---|---|
| 1 seed | 1 | Testing a single plant before committing |
| 3 seeds | 3 | A small personal grow — enough for one tent run |
| 5 seeds | 5 | Selecting the best phenotype from a few plants |
| 10 seeds | 10 | Filling a full canopy or running multiple cycles |
We'd pick the 3-pack for a first run. You get enough plants to see some variation in purple expression without committing your entire grow space. If you already know you love GDP and want to fill a 1m² tent, the 10-pack gives you room to pick the best performers.
Granddaddy Purple Auto Specifications
| Spec | Value |
|---|---|
| Seed bank | Royal Queen Seeds |
| Genetics | Purple Urkle x Big Bud Auto |
| Type | Autoflower, feminised |
| Dominance | Indica-dominant |
| THC | Up to 19% |
| Seed-to-harvest | Approximately 12 weeks |
| Indoor height | 70–120 cm |
| Outdoor height | Up to 140 cm |
| Indoor yield | Up to 450 g/m² |
| Outdoor yield | Up to 160 g/plant |
| Aroma/flavour | Sweet blueberry candy, grape, berry |
Complete your setup: pair these Granddaddy Purple Autoflower seeds with a Dark Box grow tent and a full-spectrum LED panel. Autoflowers love 18–20 hours of light throughout their entire life cycle, so a reliable light on a timer is critical. A carbon filter is non-negotiable once those terpenes start pumping in week 6 — your neighbours will smell sweet berries through the walls without one.
Why Grow Granddaddy Purple Autoflower Seeds
The original Granddaddy Purple is a photoperiod strain that demands a strict 12/12 light flip and can stretch your patience to 9–10 weeks of flowering alone. Royal Queen Seeds solved that by crossing the genetics into an autoflowering chassis. The result: you pop the seed, give it light (18/6 or 20/4 — your call), and roughly 12 weeks later you're trimming fat purple colas. No timer adjustments, no worrying about light leaks triggering hermaphrodites.
The honest limitation here is yield ceiling. A photoperiod GDP in a Sea of Green can push past 500 g/m² with extended veg time and training. This auto tops out around 450 g/m² indoors — still impressive for an autoflower, but you're trading that extra 10–15% yield potential for speed and simplicity. For most home growers running a single tent, the trade-off is worth it. You can fit two full cycles into the time a photoperiod takes for one.
Compared to something like Northern Lights Auto (another popular beginner indica auto), GDP Auto brings more visual drama and a distinctly sweeter terpene profile. Northern Lights leans earthy and spicy; Granddaddy Purple smells like you cracked open a bag of blueberry sweets. If bag appeal matters to you — and let's be honest, it does — GDP Auto wins that contest hands down.
Growing Granddaddy Purple Auto: What to Expect
Granddaddy Purple Autoflower seeds germinate quickly and push into vegetative growth within the first week. Expect broad, dark-green fan leaves and a stocky structure — this plant grows like a typical indica, staying compact and bushy rather than stretching toward the light. Indoor heights stay between 70 and 120 cm, which makes it manageable in tents as small as 60x60 cm.
- Germinate seeds using the paper towel method or directly in a small pot of lightly moistened soil. Taproots usually emerge within 24–72 hours.
- Transplant seedlings (if started in paper towel) into their final container — autoflowers dislike transplant shock, so going straight into a 10–15 litre fabric pot is ideal.
- Provide 18–20 hours of light per day from germination through harvest. A full-spectrum LED at around 200–300W actual draw covers a 1m² canopy well.
- Feed lightly during the first 2–3 weeks. Autoflowers are smaller and burn easily. Half-strength nutrients are enough until you see vigorous growth.
- Watch for the natural transition to flower around weeks 3–5. You'll see white pistils forming at the nodes without any light schedule change.
- During bloom, increase phosphorus and potassium. Drop nighttime temperatures to 15–18°C in the final two weeks to intensify purple pigmentation — this is where GDP's famous colour really pops.
- Harvest when trichomes are mostly milky with some amber (roughly week 10–12). Dry slowly in a dark room at 18–20°C and 55–60% humidity for 7–10 days, then cure in glass jars.
Flavour and Aroma of Granddaddy Purple Auto
Crack open a cured jar of GDP Auto and the first thing that hits you is sweet blueberry candy — not subtle, not background, right in your face. There's a grape undertone beneath that, almost like a berry-flavoured boiled sweet your nan kept in a tin. The smoke is thick and smooth with minimal harshness when properly dried and cured. On the exhale, you pick up a slight earthiness that grounds the sweetness and stops it becoming one-dimensional.
The terpene profile leans heavily on myrcene and linalool, which contribute to that candy-sweet, slightly floral character. According to Healthline, Granddaddy Purple is often categorised among indica strains traditionally associated with relaxation (Healthline, "12 Indica Strains for Sleep, Pain Relief, Appetite"). The aroma intensifies noticeably in the final weeks of flower — that's your carbon filter earning its keep.
Granddaddy Purple Autoflower Effects and Potency
At up to 19% THC, GDP Auto sits in a comfortable middle ground — strong enough to satisfy regular smokers, not so potent that it overwhelms someone with moderate tolerance. The effect is body-heavy and sedating, typical of indica-dominant genetics. According to Healthline's guide on indica strains, GDP is frequently listed among strains traditionally used for relaxation purposes (Healthline, 2023). A 2018 study published in the Journal of Cannabis Research noted that in 57% of sessions, cannabis users reported at least one side effect, most commonly dry mouth and dry eyes (Stith et al., 2018, PMC6164964).
This content is written for adults aged 18 and over. Dosing and effects described apply to adult physiology.
Frequently Asked Questions
How long does Granddaddy Purple Autoflower take from seed to harvest?
Approximately 12 weeks from germination to harvest-ready buds. Some phenotypes finish a few days earlier or later depending on growing conditions, but 10–12 weeks is the reliable window for GDP Auto.
What yields can I expect from Granddaddy Purple Auto indoors?
Up to 450 g/m² indoors under optimal conditions (good light, proper feeding, adequate pot size). Outdoors, expect up to 160 g per plant. Real-world results for first-time growers typically land around 300–350 g/m².
Do I need to change the light schedule for autoflower seeds?
No. Autoflowers transition to bloom based on age, not light cycle. Keep them on 18–20 hours of light from start to finish. No 12/12 flip required — that's the whole point of autos.
How do I get more purple colour from Granddaddy Purple Auto?
Drop night temperatures to 15–18°C during the final 2–3 weeks of flowering. The anthocyanin pigments in GDP's genetics respond to cooler temps by intensifying purple and deep blue hues. Warmer grows still produce good bud, but the colour won't be as dramatic.
Is Granddaddy Purple Auto suitable for beginner growers?
Yes — it's one of the more forgiving autoflower strains. The indica structure stays compact, it doesn't need light schedule management, and it handles minor feeding mistakes without dramatic stress responses. Start with the 3-pack so you can learn without pressure.
What does Granddaddy Purple Auto smell like during flowering?
Intensely sweet — blueberry candy and grape with a slight floral undertone. The smell becomes very strong from week 6 onwards. A carbon filter is critical if discretion matters to you; without one, the scent carries through walls and ventilation systems.
Can I grow Granddaddy Purple Autoflower outdoors?
Absolutely. Plants reach up to 140 cm outdoors and produce up to 160 g per plant. They perform best in warm, dry climates but the autoflower genetics mean you can start them any time temperatures stay above 15°C consistently.
Last updated: April 2026
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Medical disclaimer. This content is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before use of any substance.