Quick answer
Autoflower seeds grow best in the final pot, under 18 to 20 hours of light per day, with feed at 1/4 to 1/2 strength. Most autoflowers finish in 70 to 90 days from sprout. The plant flowers by age, not by a 12/12 light change.
Autoflower Seed Bank Recommendations: US Buyer Guide
Light schedule
Run 18 hours on and 6 hours off, or 20 hours on and 4 hours off. A 20/4 schedule adds daily light. Keep PPFD at 400 to 600 umol/m2/s in veg and 600 to 900 umol/m2/s in flower. A 12/12 schedule cuts yield for most autoflowers. Use a timer. Check for light leaks in the dark period.
how long do autoflower seeds take to grow
Pot size and planting
Plant the seed in a 3 to 5 gallon (11 to 19 L) fabric pot. Autoflower roots fill the pot fast. A small starter pot can stall growth. Sow 1 cm deep. Keep the media at 22 to 26 C (72 to 79 F). Seedlings emerge in 3 to 7 days. If you transplant, do it at 7 to 10 days, before roots circle the pot.
Water and pH
Water 5 to 10 percent of pot volume when the top 2 to 3 cm of media is dry. For a 5 gallon pot, that is 0.25 to 0.5 gallon (1 to 2 L). Keep soil pH at 6.0 to 6.5. Keep coco or hydro pH at 5.8 to 6.2. Let runoff drain. Do not let the pot sit in water. Overwatering is a common cause of slow growth.
autoflower seed bank recommendations
Feeding
Start nutrients at day 14 to 21. Use 1/4 to 1/2 of the label dose. Autoflowers have a short veg stage. Too much nitrogen in flower can delay bud set. Switch to bloom feed when pistils show at nodes. Keep EC at 1.0 to 1.6 in veg and 1.4 to 2.0 in flower. Reduce feed in the last 7 to 10 days.
Temperature and humidity
Keep lights-on temp at 22 to 26 C (72 to 79 F). Keep lights-off temp within 5 C (9 F) of lights-on. RH targets: 55 to 65 percent for seedlings, 45 to 55 percent for veg, and 40 to 50 percent for flower. Keep RH under 60 percent in late flower. Good airflow lowers mold risk. Keep VPD at 0.8 to 1.2 kPa in veg and 1.0 to 1.5 kPa in flower.
Training
Start low stress training at day 21 to 28. Bend the main stem away from the light. Tie it to the pot rim. Do not top before day 18. Top a healthy plant with 5 to 6 nodes. Remove leaves that block bud sites. Do not remove more than 10 percent of leaves in one session. Stop heavy training after week 5.
Harvest
Check trichomes on calyxes, not on sugar leaves. Milky trichomes mean peak THC. 10 to 20 percent amber trichomes mean more sedative effect. Most autoflowers harvest at 70 to 90 days from sprout. Some finish at 60 to 70 days. Dry at 18 to 21 C (65 to 70 F) and 55 to 60 percent RH for 7 to 10 days.
Common mistakes
- Starting in a small pot and transplanting late.
- Using 12/12 light for the full cycle.
- Feeding full strength at week 2.
- Watering on a fixed schedule instead of pot weight.
- Letting RH pass 60 percent in late flower.
- Harvesting by calendar date without checking trichomes.