Buds stalled growing

Hi - I've happily grown in NFT for ages.

This time I've tried SOG as opposed the the usual SCROG.

I time lapse my grows so have a photo from every day from every grow. Great for diagnostics.

This one is odd. In my SOG, I flipped to flowering when the plants were very small - i.e. around 8" tall. As you are supposed to with SOG

They continued to grow (as expected, the stretch etc) but didn't show any dense white hairy tops until 30 days. My previous grow (some same plants, from seed) showed healthy white tops from 10 days.

Growth (not flowering) has always been vigorous. When I remove leaves , there is a forest 2 days later.

This trend has continued. I'm 50 days in and the buds have just stalled. No real mass to them (I'm used to colas so heavy they fall over at this stage). They are covered well in trichs. The have just stalled. Day to day I see little change, just a little upwards growth on one strain.

One strain - the leaves are all near vertical, and partially closed. No signs of nute burn, light burn. Everything looks very healthy, except, just not much bud!

I'm confused! I'm growing 4 very different strains, all behaving the same. One straing has proper "baby" buds, that are already showing orange hairs. I'm starting to wonder if I went 12/12 far too early on my SOG and consequently everything is scaled down. I read again and again that you can start SOG flowering pretty much from seedling.

NFT
Tank temp 20c constant.
Room temp varies from 6 lights off to 20 lights on, though that "should" be irrelivant with a 20c reservoir temp.
PH well controlled.
Light well controlled.

Any ideas? Is this a consequence of SOGging too early I wonder? If it is, it doesn't explain why it took 30 days to see pistils instead of the usual 10.

Seeds can have different maturity rates, when i sog clones i like to start at 18/6 because its alot easier to control, but with seeds i generally start them at 12/12 and try to pack them in there just to help even out maturity rates, usually 3 weeks from sprout I'll have developing flowers this way.

As far as all your plants being stunted, maybe some pics along with a feed & environment history would help?

Problem is I don't want to host the photos on any of my hosting sites. Edit: pics below

At the moment after a long evening thinking, I'm putting it down to the cold.

I have read that with NFT all you need to do is keep the res. at around 20c.

But my thinking is this:

1) The whole grow has been a winter grow (in an outbuilding). Dropping below 9 amost every night.
2) plant metabolism slows when cold. - this explains slow flowering (I have cuttings and seedlings , 4 different plant types, 12 plants, all exhibiting the same stunted behaviour).
3) Nutes, light, etc, I'm well on top of. Nothing out of the ordinary. They get Ionic Hydro bloom at around 1500ms. I keep it at 5.8-6.5ph. Always been happy with those numbers. No signs of underwatering (NFT...), No signs of overwatering. Plants all look very very healthy, apart from just not producing much.
4) Leaves pointing straight up and closing (curling in) indicates the plant doesn't want light. I'm guessing because it can't get food, because it's metab. is so slow. That or mag deficiency, again, because it can't take it up because the metab. is so low.
5) although I read about heating the res, I'm assuming this works as the plants draw up the water, which warms them up. But when it's very cold I'm assuming that this is not enough. Much like standing in a warm bath, in the freezing cold, naked, doesn't warm us up enough! I do also have some purple leaf stems showing on the plants that are pointing straight up (only one type is like that, the other three look normal, albeit with not much bud material)

The only fly in the ointment is that the leaf growth has, up till now, been very vigorous, which doesn't really indicate a slow metabolism! Unless of course producing flowers requires a whole lot more. I've also never had plants take 3 weeks to show decent pistils, yet they still gained height well.

Aha! - how to atatche pics. Ok, first pic is the size they were when flipped to 12/12 (normally I have just 4 and scrog them much bigger).


Next up, after 20 days(!!) of 12/12 Note hardly any pistils yet. Very odd.



Now, after 30 days of 12/12 below. What I expect after 10 days normally, and I've grown the same plants, from seed and cuttings.



Now, roll on to 50 days.: Prety piss poor. The white pistils on the back plants (bubblegum Pro+) are just fluffy "nothings". Notice how the front plants (Mandala #1) have pointed skywards (and you can't see but are covered in trichs) and the leaves have curled inwards.



Last night I put a heater in. I'll know in a few days. On my first grow ages ago it got too cold and they stalled at veg (and I didn't have a res heater). When I added heat it took about 3 days for things to kick off again.

For reference, this is what I'm used to at around 60 days of 12/12, scrog. 600w hps.

A little closre on this. I'm certain its temperature now.

Bubblegum pro at the back are continuing to bud - albeit quite slowly.
Mandala #1 at the front are still stalled, and now the leaves are going deep purple - a good sign of too cold.

Seems cold is most likely, and the Bubblegum is more tolerant than the Mandala.

Everything else checks out fine. I'm maintaining 15 c min in the dark now, and it peaks at mid 20' in the light. I don't think even 15 is enought for the Mandala, but it has certainly sprung the bubblegum back into life after a week of heating.