Cannabis Flowering Weeks 1 and 2: What to Expect
In weeks 1 and 2 after the flip to 12/12 (photoperiod plants only), plants stretch and the first white pistils appear. Give them headroom, keep the dark period truly dark, and change one thing at a time. Autoflowers follow their own clock and do not need a light change.
The first two weeks of flower can feel busy. Plants grow fast, their needs shift, and small mistakes show up quickly. Below, you’ll find when week 1 starts, what to expect in each week, what to do, and how to fix common problems.
When week 1 starts
For photoperiod plants, flowering is triggered by longer nights. UF/IFAS Extension explains that hemp and hops are short day plants, which means they flower once day length drops below a certain threshold, and that threshold varies by cultivar. Indoor growers trigger this by switching the lights to 12 hours on and 12 hours of full darkness, often called the flip.
Week 1 starts the day you flip. Outdoors, flowering starts on its own as summer days shorten, so there is no single start date. You will usually notice the change a little later, when growth speeds up and the first flowers form.
How you count weeks matters more than it seems, later on. NC State Extension notes that seed companies and breeders increasingly recommend harvesting based on weeks after floral initiation. So keep a note of your flip date, and later of the date you first see pistils. Those two dates make breeder flowering times much easier to use.
Week 1: the stretch begins
The biggest change in week 1 is height. Many plants grow quickly once the nights get longer, putting on new stem length and spacing between nodes. Sensi Seeds notes that most cannabis plants stretch once they move into bloom, sometimes doubling or tripling in size, and that indica types typically stretch less.
How much your plants stretch depends on genetics and conditions, so there is no fixed number to plan around. Tall, sativa leaning strains tend to stretch most. Compact, indica leaning strains often stretch less. Strong, close light can also keep stretch in check.
Week 1 is also a good time to watch your plants’ appetite. Fast growth means they may drink more water. Keep feeding steady rather than making big changes, and check that the light is not too close as the tops rise.
For most training, this is the last good window. Gentle bending and tying down can still spread the canopy before buds start to form. Heavy cuts are better done before the flip.
Week 2: first pistils
Week 2 is usually when growers see the first clear signs of flowering. Azarius notes that week 2 is when the first white pistils typically emerge at the bud sites. These are the fine white hairs that grow from the calyxes where branches meet the stem and at the tops of the plant.
University of Nevada, Reno Extension explains what they are for: the stigmas extend past the bract, the small leaves around the reproductive cells, to catch male pollen. In a seedless grow, there is no pollen to catch, so the flowers keep developing into buds.
Timing varies. Some plants show pistils within days of the flip, while others take longer. The stretch usually continues through week 2 as well, so keep watching your headroom.
Week 2 is also when you may see males or intersex plants. Look closely at the same bud sites. Pollen sacs look like small round balls on short stems, with no white hairs. For help telling them apart, see our guide to early female signs at https://kindseed.com/detecting-early-female-plant-signals-like-a-pro/.
What to do in weeks 1 and 2, step by step
- Photoperiod plants only: switch to 12 hours on and 12 hours of full dark. Autoflowers do not need a light change.
- Leave room above the canopy for the stretch.
- Check the dark period for light leaks.
- Keep feeding steady and change one thing at a time.
- Watch for white pistils at the bud sites. They often show around week 2, but timing varies.
- Do any training early, before buds start to form.
To check for light leaks, step inside your grow space during the dark period, let your eyes adjust, and look for any light coming through zippers, seams or vents. Even small leaks are worth fixing.
Autoflowers and the flip
Autoflowers don’t respond to day length in the same way. They start flowering on their own after a few weeks of growth, whatever the light schedule. So there is no flip and no week 1 in the usual sense.
Many growers keep autoflowers on the same long light schedule from seed to harvest. You will still see a stretch and the first pistils, but the timing comes from the plant’s age, not from a light change. Count weeks from when you first see pistils.
If you grow autoflowers and photoperiod plants in the same space, remember that switching to 12/12 for the photoperiod plants will also shorten the light for the autoflowers. This cuts their light hours and may reduce growth.
Troubleshooting
| Sign | Likely cause | What to do |
|---|---|---|
| Plant is hitting the light | Stretch | Raise the light or bend branches gently |
| No pistils by week 3 | Timing varies, or light leaks | Check the dark period and wait a few days |
| Pollen sacs show up | Male or intersex plant | Isolate or remove confirmed pollen plants |
| Yellowing lower leaves | Possible causes: feeding change or pH | Check pH and feed one at a time |
Most problems in early flower come from light, either too close or leaking into the dark period. Fix those first before changing your feed.
If a plant looks stressed, resist the urge to fix everything at once. Make one change, wait a few days, and see how new growth responds. Early flower is a busy time for the plant, and a calm, steady room usually does more good than a string of quick adjustments.
Room habits that matter
Keep the schedule consistent. Use a reliable timer and do not open the space during the dark period unless you have to. Even dim light can disrupt flowering, so keep checks very brief.
Watch humidity. As plants grow bigger, they release more moisture. Keep air moving around and through the canopy, and lower humidity gradually as buds start to form to reduce the risk of mold later.
Keep notes. Record your flip date, the day pistils first appear, how much each plant stretched, and any changes you make. Next time you grow the same strain, you will know what to expect. If you plan to try more advanced techniques later in flower, see our guide on schwazzing at https://kindseed.com/schwazzing-to-increase-your-yield/.
Sources: UF/IFAS Extension HS1452 (https://ask.ifas.ufl.edu/publication/HS1452). NC State Extension, Visual Guide to Floral Hemp Maturation (https://hemp.ces.ncsu.edu/visual-guide-to-floral-hemp-maturation/). University of Nevada, Reno Extension, Hemp Basics: Anatomy of a Female Hemp Plant (https://extension.unr.edu/publication.aspx?PubID=4479). Sensi Seeds, Flowering stage week by week. Azarius, Flowering stage week by week.
FAQ
What happens in week 2 of flowering?
In week 2, most photoperiod plants keep stretching, and the first white pistils often appear at the bud sites. Timing varies by strain and conditions. It is also when you may first spot pollen sacs on male or intersex plants, so check the bud sites closely.
How much do plants stretch in weeks 1 and 2?
It varies. Some plants grow a lot taller after the flip, while others stretch only a little. Tall, sativa leaning strains often stretch most, and compact strains less. Leave room above the canopy and train early rather than counting on a set amount.
When do pistils appear?
White pistils often appear around week 2 after the flip, but timing varies. Some plants show them within days, others later. If you see none by week 3, check your dark period for light leaks and give the plants a few more days.
Should I change nutrients at the flip?
Keep feeding steady and change one thing at a time. Plants may drink more during the stretch, so watch water use. Many nutrient lines suggest a gradual shift toward a bloom feed, so follow your product label rather than making a sudden switch.
Do autoflowers have a week 1 of flower?
Not in the same way. Autoflowers start flowering on their own based on age, not day length, so there is no flip. Count weeks from when you first see pistils, and keep the light schedule steady.
