Flipping To Flower

Indoors, you decide when the plant flowers. Outside, shortening days do it in late summer. In a tent, you do it by changing the timer from 18 hours of light to 12 hours of light and 12 hours of uninterrupted darkness.

That is the whole mechanism. One timer change, and over the next ten to fourteen days the plant stops making leaves and starts making flowers.

It is also the last decision you can make about plant size. After the flip, the plant is going to stretch to roughly double its height, and nothing you do will stop it. People who flip too late end up with colas pressed against the LED, bleaching white. People who flip too early get a small plant and a small harvest.

If you are running autoflowers, you can skip most of this page. Autos flower on their own schedule regardless of light hours, and most growers leave them on 18/6 start to finish. The environment and feeding changes below still apply, they just happen when the plant decides rather than when you do.

When to flip#

The rule is simple: flip when the plant is one third to one half of the height you want at harvest.

Work backward from your tent. In a four foot tall tent, subtract about a foot for the light and its hanging distance and about a foot for the pot. You have roughly two feet of usable vertical space, so you want a finished plant around 24 to 30 inches, which means flipping at 10 to 14 inches.

In a taller tent, five or six feet, you have more room and can veg longer. Most beginners in a standard tent flip somewhere between week four and week six from sprout.

Indica leaning strains stretch about 50 percent. Hybrids roughly double. Sativa leaning strains can triple, which is a real problem in a short tent. If your seed pack says sativa or "haze" anywhere on it, flip earlier than you think.

What to do the day before#

Get the housekeeping done while you can still reach into the plant.

Clean out the bottom third. Anything down there is getting almost no light and will only ever produce tiny airy buds that take forever to trim. Remove those small lower branches and the leaves around them entirely. Growers call this lollipopping, because you end up with bare stem at the bottom and everything concentrated up top.

Finish any topping (you should have stopped two weeks ago anyway). Check every plant tie and loosen any that are digging in. Put a trellis net in now if you are using one, because installing one over a flowering plant is miserable.

If your plant has not been repotted and roots are circling the bottom of the pot, do it now. Transplanting after the flip stalls the plant during the exact window when it should be stretching.

Setting the timer and sealing the tent#

Set your timer to 12 hours on, 12 hours off. Most growers run lights on overnight and off during the day, because the tent stays cooler when the lights are on at night and you get a free temperature drop.

The dark period has to be actually dark. Interrupting it, even by opening the tent to check on things with the room light on, can confuse the plant into revegging or throwing male flowers on a female plant. Tape any light leaks around the zipper. The small green LED on your power strip is not a problem. A gap of daylight down the seam is.

Do not go in the tent during dark hours for the first three weeks. After that, a quick peek with a green headlamp is usually tolerated, though the honest answer is that nobody needs to be in there in the dark.

The stretch#

Days 1 through 14 after the flip, the plant grows fast and vertically. It will look almost alarming. Nodes space out, stems lengthen, and the whole structure gets taller and looser.

Raise your light as it grows. Keep the same distance the manufacturer recommends, usually 12 to 18 inches in flower for a mid-power LED. If the top leaves start bleaching white or curling up at the edges, the light is too close.

You can still do light stress training during the stretch. Tying down anything that is running away from the rest of the canopy is the easiest way to keep a flat top. Stop around day 14 to 18, when stems get stiff and brittle.

Around day 14 to 21 you will see the plant switch modes: vertical growth stops, and the little clusters at each node start swelling and putting out white hairs. That is flower.

Telling males from females#

Around day 7 to 21 after the flip, look at the nodes where branches meet the main stem.

Female: a small teardrop shaped calyx with one or two thin white hairs (pistils) coming out of it. This is what you want.

Male: small round or oval sacs on little stalks, usually in grape-like clusters, with no hairs.

If you bought feminized seeds, everything should be female, and mislabeling is rare but not impossible. If you bought regular seeds, expect roughly half males.

Get males out of the tent the day you identify them. When those sacs open they release pollen, and pollen turns your entire harvest into seeds. Do not walk the plant through the tent. Bag it, then take it out.

Changing the food and the air#

Switch from your grow (high nitrogen) nutrient to your bloom (higher phosphorus and potassium) nutrient over the first two weeks. If you have a two bottle system, taper: half grow and half bloom for a week or so, then bloom only.

Start at half the dose on the bottle. Bottle labels are aggressive, and for a first grow you would rather be slightly under fed than burnt.

Environment changes too:

• Humidity down. Veg is comfortable at 55 to 65 percent. Bring flower down to 45 to 55 percent, and lower still, 40 to 45, in the last few weeks. Dense buds plus humid air equals bud rot.
• Temperature. Keep lights-on temps around 75 to 80F. A small drop at night is fine and helps color in some strains.
• Airflow. Keep the clip fan moving air through the canopy. Still air inside a thickening plant is the single biggest mold risk you have.

What you should expect#

Nothing looks like weed for about three weeks. That is normal. Week one and two are all stretch, week three is when white pistils appear everywhere, and real bud shape shows up around week four.

Next up is what actually happens each week of flower, and what to change as you go.