Buying Granddaddy Purple (GDP) for an indoor grow comes down to one number: 8 to 11 weeks of flowering. That range is the practical answer you will find across breeder listings and grower reports. If a seller promises a 6-week finish or a 14-week marathon, treat that as a signal to ask harder questions. Convenience matters when you are choosing seeds versus clones, but convenience should not override genetic reliability. The most reliable purchases name the breeder, state whether the plant is photoperiod or autoflowering, and give a flowering window rather than a single figure.
What flowering time actually measures
Indoor flowering time is counted from the day you switch to a 12/12 light schedule, not from seed. Some growers start counting when the first pistils appear, which adds roughly 7 to 14 days. That difference explains why two growers with the same clone can report 8 weeks and 10 weeks for the same plant. When you compare listings, check which starting point the breeder uses.
Parameter bands for indoor GDP
- Flower length: 8 to 11 weeks, with most phenotypes finishing near 9 to 10.
- Vegetative time: 3 to 6 weeks from clone or seed before flip, depending on tent height.
- Light schedule: 12 hours on, 12 hours off for photoperiod plants. Autoflowering versions run 18/6 or 20/4 from start to finish.
- Height: compact to medium, often 3 to 5 feet indoors with training.
- Yield: moderate to heavy when light intensity and root space are adequate.
- Night temperatures: cool nights in late flower can help purple expression, but they are not required for potency.
What to look for before you buy
Ask for the breeder name, the generation (F1, S1, clone-only), and whether the line is stabilized. A stabilized line gives you more uniform flowering times. Unstable lines can split into 8-week and 12-week phenotypes in the same pack. For indoor growers, uniformity saves space and scheduling headaches.
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Check the seller's return policy and germination terms. A convenience-focused purchase, such as a clone shipped overnight, still depends on the mother plant's health. If the seller cannot tell you the mother's flowering window, the convenience is not worth the risk.
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Common pitfalls
- Confusing autoflower and photoperiod listings. Autoflowers finish on their own schedule and often run 8 to 10 weeks from sprout, not from flip.
- Trusting a single flowering number. Breeders round down. A plant labeled 8 weeks may need 10 weeks for full ripeness.
- Expecting purple without cool nights. GDP can stay green indoors if temperatures stay warm. Color is cosmetic, not a quality marker.
- Buying clones from an unknown source. Pests and pathogens travel with convenience.
- Harvesting by calendar instead of trichomes. Cloudy trichomes with some amber is the reliable signal.
FAQ
How long does Granddaddy Purple flower indoors?
Most indoor growers report 8 to 11 weeks after the light flip. Plan for 10 weeks and adjust based on trichome color.
Can Granddaddy Purple finish in 7 weeks indoors?
It is possible with a fast phenotype under strong light, but 7 weeks is early for most GDP plants. Check trichomes rather than trusting a short claim.
Does Granddaddy Purple turn purple indoors?
Sometimes. Purple expression depends on genetics and cooler late-flower temperatures. A green phenotype can still deliver the same effects.
Are seeds or clones more convenient for indoor GDP?
Clones save time and offer predictable flowering, but they carry pest risk and limited availability. Seeds are easier to source and store, though flowering times vary more within a pack.
What light schedule should I use?
Use 12/12 for photoperiod GDP. Keep the dark period fully dark to avoid stress and delayed flowering.