The Official Cannabis Independent strain guides
Granddaddy Purple No 17 Shop
The Official Cannabis collection · sheet 17No 17 · Granddaddy PurpleGrow

Growing

Growing Granddaddy Purple: flowering time, yield and breeder specs

Most listings put Granddaddy Purple’s indoor flowering at about 55–65 days (Royal Queen Seeds, Leafly, Weedmaps), with two seed lines at about 77–80 days, and outdoor harvests in late September or early October in the Northern Hemisphere. It stays short and compact, and Leafly rates it easy to grow.1,2,3,4,5

Breeder specs side by side

Source and versionFloweringIndoor yieldOutdoorDifficulty
Royal Queen Seeds, feminized (data sheet)55–65 days; its text says 8–10 weeks450–500 g/m²; 70–120 cm tallEarly October; 550–600 g per plant; 120–150 cm1—
Royal Queen Seeds, autoflower (data sheet)55–60 days; 70–85 days from germination375–450 g/m²; 70–120 cm tall110–160 g per plant; 80–140 cm6—
United Cannabis Seeds, feminized (SeedFinder listing)About 80 days—About 90 cm at maturity5—
Grand Daddy Purp, Ken Estes’s regular seeds (SeedFinder listing)About 77 days; its text says 8–14 weeks—Indoors or outdoors4—
Apothecary text (SeedFinder)8–9 weeks0.5–3.5 oz per plant; about 3 ft tallUp to 8 ft; 8 oz to 5 lb per plant7Easy to work with7
ILGM, feminized———Beginner8
Leafly (strain page)7–9 weeks; 60 days in its descriptionHigh; short plants—Easy2
WeedmapsAbout 65 days indoors—Late September to early October (Northern Hemisphere)3—

Seed-company figures are the sellers’ own claims.

What the plant is like

Expect a short, compact plant. Weedmaps describes short plants with tight internodal spacing, Leafly rates its height short, United Cannabis Seeds says it reaches about 90 cm, and Royal Queen Seeds calls its version sturdy and low-maintenance.1,2,3,5 The Apothecary text describes a short, bushy plant that branches extensively, which it says makes it less than ideal for sea-of-green setups.7

Yield is part of its story. Leafly’s history of the Purps says Granddaddy Purple was more easily cultivated than earlier purple strains thanks to its higher-yielding Big Bud parent, and Leafly’s strain page credits it with massive yields; Ken Estes, by contrast, says the Purple Medicine plant he started from yielded only about a pound per light.2,9,10

What to watch for

Dense, resinous buds. The Apothecary text warns that its high resin output and dense structure can attract mites, and Leafly recommends excellent air circulation, clearing lower branches, 70–80°F and 50% humidity; Weedmaps says it grows best in a climate-controlled environment.2,3,7

Getting the purple

The color comes from anthocyanins, pigments some strains carry more of than others, and purple hues may appear when temperatures drop; Leafly notes that a purple plant exposed to cold may produce less THC, and says Granddaddy Purple “seems to always carry swirls of deep purples and pastel lavenders”.11

Growers Leafly interviewed for its history of the Purps are more cautious. Breeder Todd McCormick credits Afghan genetics for the purple in broad-leaf cannabis, Purple City Genetics says temperature and light both affect anthocyanin, Ghost of ABF Genetics says “If it’s only a matter of temperature, then it’s not purple”, and the article adds that sometimes even Granddaddy Purple doesn’t come out purple.9

Seeds and the law in the US

Under the amended federal definition of hemp, viable seeds from cannabis plants above 0.3% total THC, including THCA, are not hemp.12 Congress delayed that exclusion, with most of the new definition, from Nov 12 to Dec 11, 2026; only the exclusion of products with cannabinoids the plant cannot produce naturally starts on Nov 12.13 Home cultivation rules are set by each state. This site does not sell seeds.

Sources

  1. Royal Queen Seeds, Granddaddy Purple feminized seeds (data sheet). Accessed Oct 4, 2026.
  2. Leafly, Granddaddy Purple (aka GDP) strain information. Accessed Oct 4, 2026.
  3. Weedmaps, Granddaddy Purple strain page. Accessed Oct 4, 2026.
  4. SeedFinder, Grand Daddy Purp (Grand Daddy Purp): strain info, cannabinoids and genealogy. Accessed Oct 4, 2026.
  5. SeedFinder, Granddaddy Purple (United Cannabis Seeds): strain info. Accessed Oct 4, 2026.
  6. Royal Queen Seeds, Granddaddy Purple Auto seeds (data sheet). Accessed Oct 4, 2026.
  7. SeedFinder, Grand Daddy Purple (Unknown or Legendary): strain info and Apothecary breeder description. Accessed Oct 4, 2026.
  8. ILGM, Granddaddy Purple feminized seeds. Accessed Oct 4, 2026.
  9. Leafly, Pleased as Purple Punch: a ‘Purps’ family genealogy (Amelia Williams) (2021-04-08). Accessed Oct 4, 2026.
  10. Leafly, Meet the daddy of Granddaddy Purple (Lindsay MaHarry) (2026-07-21). Accessed Oct 4, 2026.
  11. Leafly, How does cannabis get its color? Here's why some strains turn purple (Bailey Rahn) (2020-07-28). Accessed Oct 4, 2026.
  12. Congressional Research Service, Changes to the statutory definition of hemp and implications for agricultural policy (IF13136) (2026-09-28). Accessed Oct 4, 2026.
  13. U.S. Government Publishing Office, Continuing Appropriations and Extensions Act, 2027 (P.L. 119-103), sec. 2019. Accessed Oct 4, 2026.