Granddaddy Purple Grow Guide: Flowering Time and Yield

Quick answer

Granddaddy Purple (GDP) is an indica-dominant strain bred from Purple Urkle and Big Bud. Flowering runs 8 to 11 weeks indoors. Indoor yields land near 400 to 500 grams per square meter. Plants stay short and bushy, so they fit small tents and screen of green setups. The purple color comes from cool nights late in flower, not from a nutrient bottle.

granddaddy purple strain yield

Genetics and background

Ken Estes bred Granddaddy Purple in the San Francisco Bay Area in 2003. The parent list is Purple Urkle crossed with Big Bud. Reported THC sits between 17 and 23 percent. The aroma is grape, berry, and sweet earth.

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Setup

• Grow space: 4 to 5 feet of vertical room per plant, plus light clearance.
• Light: 600W HPS or a 300W to 480W LED board per square meter.
• Medium: soil, coco, or hydroponic. Soil buffers the heavy feeding this plant wants.
• Training: top once or twice, then use a screen. Stems stiffen after week 3 of flower.
• Climate: 70 to 80 F in the day, 60 to 70 percent humidity in veg, 40 to 50 percent in flower.

Flowering time and yield

Switch to 12/12 after 4 to 6 weeks of veg. Stretch is moderate, often 50 percent of final height. Buds bulk in weeks 5 through 8. Indoor harvests finish in 60 to 77 days. Outdoor plants finish in late September to mid October in the northern hemisphere. Outdoor yields run 400 to 600 grams per plant in warm, dry climates. Cold, wet falls invite bud rot on dense colas.

granddaddy purple strain effects

Turning the buds purple

Anthocyanins create the purple pigment. These compounds build when night temperatures fall 10 to 15 F below daytime readings. Aim for nights in the 50s F and days near 70 to 75 F during the last 2 to 3 weeks. Purple color is cosmetic. It does not raise THC.

Feeding

Granddaddy Purple feeds heavy in veg. Keep nitrogen available until week 3 of flower, then cut it back. Raise phosphorus and potassium from week 4. Flush for 7 to 10 days before harvest.

Common problems

• Bud rot in humid rooms or rainy outdoor falls.
• Spider mites on dense lower growth. Defoliate the bottom third.
• Root rot in coco or hydro when the medium stays wet.

Harvest and cure

Check trichomes with a loupe. Chop when most heads are cloudy and a few turn amber. Dry 7 to 10 days at 60 F and 60 percent humidity. Cure in jars for 2 to 4 weeks and burp daily for the first week.