Advice on triggering flowering outside

AthelR · Aug 4, 2025

This is our first photoperiod plant, and the first outside. We have a very healthy plant - now 2 metres high, in a poly tunnel, with lots of growing tips. All good.

But I’m reading that the plant will not start to produce colas until daylight hours reduce to 12, which is on September 21. Allowing 6 - 8 weeks for cola development takes me into November. In the UK it’s getting chilly and temperatures can fall to low, not much sun.

Is that just how it is, or have I misunderstood something? Is it worth trying to trigger cola production earlier by using some blackout curtains?

Any advice would be much appreciated. Thanks!

Ninjadogma · Aug 4, 2025

AthelR said:
This is our first photoperiod plant, and the first outside. We have a very healthy plant - now 2 metres high, in a poly tunnel, with lots of growing tips. All good.

But I’m reading that the plant will not start to produce colas until daylight hours reduce to 12, which is on September 21. Allowing 6 - 8 weeks for cola development takes me into November. In the UK it’s getting chilly and temperatures can fall to low, not much sun.

Is that just how it is, or have I misunderstood something? Is it worth trying to trigger cola production earlier by using some blackout curtains?

Any advice would be much appreciated. Thanks!

Thats not really true. Outside in nature, cannabis plants are triggered into flowering when they begin to be subjected to 10 hours or more of uninterrupted darkness. So they start creeping into flower on the date when daylight hours shorten to 14 hours. The date you are referring to is the Equinox, when the days and nights are about equal length and when the Equinox hits, you should expect to roughly be at the midway point of flowering. There can be a good 3 week difference between the timing of various strains moving into flower and finishing.

AthelR · Aug 4, 2025

Ninjadogma said:
Thats not really true. Outside in nature, cannabis plants are triggered into flowering when they begin to be subjected to 10 hours or more of uninterrupted darkness. So they start creeping into flower on the date when daylight hours shorten to 14 hours. The date you are referring to is the Equinox, when the days and nights are about equal length and when the Equinox hits, you should expect to roughly be at the midway point of flowering. There can be a good 3 week difference between the timing of various strains moving into flower and finishing.

Thanks ninjadogma. That’s really helpful. I was misled by info I found through AI. 14 hours sounds much more like it.

Galgrows · Aug 4, 2025

But if you want to introduce flowering throw a black tarp or plastic over the top of the tunnel really black it out, then you remove it for as long as you want during the sunlight hrs.

Ninjadogma · Aug 4, 2025

AthelR said:
Thanks ninjadogma. That’s really helpful. I was misled by info I found through AI. 14 hours sounds much more like it.

Where a lot of us get hung up is thinking they need 12 hours of light to flower when in reality they need 10 hours or more of darkness.

Ninjadogma · Aug 4, 2025

Galgrows said:
But if you want to introduce flowering throw a black tarp or plastic over the top of the tunnel really black it out, then you remove it for as long as you want during the sunlight hrs.

Nice thing about growing in containers, I just put them to bed in the shed and let them sleep in late. May thru July is the only time that's necessary for me. The rest of the year I'm throwing plants in there to give em longer days.

Week4Bytch · Aug 4, 2025

AthelR said:
This is our first photoperiod plant, and the first outside. We have a very healthy plant - now 2 metres high, in a poly tunnel, with lots of growing tips. All good.

But I’m reading that the plant will not start to produce colas until daylight hours reduce to 12, which is on September 21. Allowing 6 - 8 weeks for cola development takes me into November. In the UK it’s getting chilly and temperatures can fall to low, not much sun.

Is that just how it is, or have I misunderstood something? Is it worth trying to trigger cola production earlier by using some blackout curtains?

Any advice would be much appreciated. Thanks!

I'd say yes, if you can do it on the daily cover that thing up. Get your flower on.

MJmadscientist · Aug 4, 2025

Not sure where your at but we already see flower 13 hours north of me and where I’m at. You should have some stretch and a hair or two showing by now.

What’s your length of day right now?

AthelR · Aug 5, 2025

Ninjadogma said:
Nice thing about growing in containers, I just put them to bed in the shed and let them sleep in late. May thru July is the only time that's necessary for me. The rest of the year I'm throwing plants in there to give em longer days.

Galgrows said:
But if you want to introduce flowering throw a black tarp or plastic over the top of the tunnel really black it out, then you remove it for as long as you want during the sunlight hrs.

Thanks Galgrow. I am not sure I need to? Now I know it will flower at the end of August, we can harvest mid-October which will probably work as long as we get some sun in October.

AthelR · Aug 5, 2025

Ninjadogma said:
Where a lot of us get hung up is thinking they need 12 hours of light to flower when in reality they need 10 hours or more of darkness.

Yes. I think AI got it wrong because for indoor growing flowering is triggered by going below the 14 hour mark and growers tend to do 12-12 to kick start it. I should have checked what AI said...

AthelR · Aug 5, 2025

Week4Bytch said:
I'd say yes, if you can do it on the daily cover that thing up. Get your flower on.

I am seriously thinking about that...

AthelR · Aug 5, 2025

MJmadscientist said:
Not sure where your at but we already see flower 13 hours north of me and where I’m at. You should have some stretch and a hair or two showing by now.

What’s your length of day right now?

Southwest England. Its currently 15. It drops to 14 on August 25.

MJmadscientist · Aug 5, 2025

AthelR said:
Southwest England. Its currently 15. It drops to 14 on August 25.

When is your first frost? You may have an even longer growing season than us. That’s not a bad thing.
If you start playing with like now you will shorten your stretch time and that’s bud your missing out on. If no frost comes to worry about natural light draws out flowering more and may give you more development of future flower sites.
“you can always cover plant if frosting overnight”.

AthelR · Aug 5, 2025

MJmadscientist said:
When is your first frost? You may have an even longer growing season than us. That’s not a bad thing.
If you start playing with like now you will shorten your stretch time and that’s bud your missing out on. If no frost comes to worry about natural light draws out flowering more and may give you more development of future flower sites.
“you can always cover plant if frosting overnight”.

Good point. However the plant is already huge. I’ve removed many growing tips because there were too many on each branch. We still have probably 30 - 50 tips where a cola might appear. We won’t get frost in October but the sunlight might be weak. What do you think?

MJmadscientist · Aug 5, 2025

AthelR said:
Good point. However the plant is already huge. I’ve removed many growing tips because there were too many on each branch. We still have probably 30 - 50 tips where a cola might appear. We won’t get frost in October but the sunlight might be weak. What do you think?

I wouldn’t worry about it. You’ll follow a timeline similar to me. Your light hours don’t drop at a significant rate in comparison to in the USA.

Are you worried about her being seen? If so send pictures. This may be a perfect opportunity to super crop her with some lst/hst training combos.
You have the time to recover any she will stretch while she finished mending those knuckles you create.
Plus….. More big ass colas for your troubles. You’re opening up the nodes and bud sites to more light and in return you’ll get very consistent growth across a lower horizontal canopy.

AthelR · Aug 5, 2025

MJmadscientist said:
I wouldn’t worry about it. You’ll follow a timeline similar to me. Your light hours don’t drop at a significant rate in comparison to in the USA.

Are you worried about her being seen? If so send pictures. This may be a perfect opportunity to super crop her with some lst/hst training combos.
You have the time to recover any she will stretch while she finished mending those knuckles you create.
Plus….. More big ass colas for your troubles. You’re opening up the nodes and bud sites to more light and in return you’ll get very consistent growth across a lower horizontal canopy.

That all sounds very interesting. We’re not worried about her being seen… we’re worrying about her being smelt when we get to the end stages. But those training techniques sound promising. How can I learn how to do that? I took these pics 2 weeks ago. We’ve thinned it since then.

MJmadscientist · Aug 5, 2025

AthelR said:
That all sounds very interesting. We’re not worried about her being seen… we’re worrying about her being smelt when we get to the end stages. But those training techniques sound promising. How can I learn how to do that? I took these pics 2 weeks ago. We’ve thinned it since then.View attachment 2492462 View attachment 2492463 View attachment 2492465 View attachment 2492463

Oh yeah. That’s screaming potential. You have any bamboo strips for stakes,wood stakes, fiberglass electric fence poles?
You can make your own stakes if need be. You get some tie wire or can use any type of plant ties.

Also with a helping hand and some concrete reinforcement mesh or other types of fencing “plastic” with roughly 4 inch squares in it.
You hang it on 4 corners by yours stakes and start being it down on top of the plant while pulling the branches back underneath the mesh grid.
This may be the easier of the two since you haven’t tied one down before and it has more risk of snapping branches.
If you snap one with the grid system you just tie that branch to the grid and move on. Keeps producing just the same.

Basically you’re gonna pull back all those branches to the outside and space them out even so light hits them all the same. That’s with either one.

Yours will still be slightly above horizontal cause she’s already a decent size plant. I suspect the stems are already woody yes?

Also idk how close your nearest nose of haters lives but that plants gonna stink a lot no matter what.

You don’t have English box hedges available where you are?
They smell like skunk weed in warm weather. There anre others that smell of the dank too in the box hedge family. It’s quite overwhelming in the hot months at apartments with them in mass around the complex.

MJmadscientist · Aug 5, 2025

This gives you an idea. These are kept really low profile.
You can see however that they start off like the one circled in red and end up like the two on the very bottom.

All the light is even across the canopy. Then because of them being level the hormones and nutrients reach them all equally as well.

AthelR · Aug 6, 2025

MJmadscientist said:
This gives you an idea. These are kept really low profile.
You can see however that they start off like the one circled in red and end up like the two on the very bottom.

All the light is even across the canopy. Then because of them being level the hormones and nutrients reach them all equally as well.

Thanks! We will start training the plants. I like your vegetable patch. Some nice courgettes coming too!

nekvt1 · Aug 6, 2025

I'm in northern New England and my girls have started to pre flower already and we are currently at 14 1/2 hrs of daylight. My Atlas Snow Panda fast photo is in full flower. I'd definitely recommend the Snow Panda for anyone with a shorter growing season.

Advice on triggering flowering outside

Advice on triggering flowering outside

AthelR

Ninjadogma

AthelR

Galgrows

Ninjadogma

Ninjadogma

Week4Bytch

Loyal To The Soil

MJmadscientist

AthelR

AthelR

AthelR

AthelR

MJmadscientist

AthelR

MJmadscientist

AthelR

MJmadscientist

MJmadscientist

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nekvt1

Advice on triggering flowering outside

Advice on triggering flowering outside

AthelR

Ninjadogma

AthelR

Galgrows

Ninjadogma

Ninjadogma

Week4Bytch

Loyal To The Soil

MJmadscientist

AthelR

AthelR

AthelR

AthelR

MJmadscientist

AthelR

MJmadscientist

AthelR

MJmadscientist

MJmadscientist

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AthelR

nekvt1

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