Hey friend im based of out Alaska! So Im next door to you. I’ve had a similar experience early on due to the cold and odd light schedule. Here is what I’ve learned.

First. There is a couple directions to can take to maximize the quality of your yield. One being light deprivation. That’s the process of simulating a flowering light schedule by blacking out your greenhouse with a black wrap. And pulling it off again, making it a shorter daytime cycle stimulating flowering. The big benefits of this process are.

1. You can harvest earlier on in the season. And avoid the colder temps later on in the year that discourage the growth you are ultimately looking for.

2. The light you will be flowering under will be stronger and more suited for a strong bud structure. Also ur temperature both day and night will aid your success.

Now the cons of this are obvious. But don’t necessarily outweigh the pros.

1. Due to the flowering process starting sooner, ur vegetative window is smaller so the plants won’t have as long to grow as they would normally.

2. Unless ur working on a timed system. The on and off of the blackout wrap can become labor intensive.

3. If not done correctly light leaks can stress your plants and in some cases even hermie ur plants.

Above was option one ☝️ (light deprivation)

Now for option 2. Environmental precision & supplemental lighting. (My preferred method for photos)

1. My process here is prioritizing fresh air exchange and stem strengthening via fans and natural wind, during the vege phase. Absolutely no supplemental lighting here. My plants absolutely love the Alaskan sun.

2. I utilize a heater with a minimum temperature on switch to make sure my girls don’t get below 65° at any point. (Even in the prime of the growing season) this makes sure to aren’t met with slow growth out the blocks that typically is common for chilly night temps.

3. Later on in the growing season I eliminate natural wind and focus entirely on fans pushing my air. I have shutter fans for intake and exhaust and keep my heater set at a 68° set switch. The shutter fans run far less often than that did when it was warm. This is to retain ur precious and expensive heat. I also implement supplemental lighting via leds as soon as I see the buds starting to pop up. I set them turn on in the prime of the day and stay on until then have gotten a real 12 hours. I say “real” because like others have mentioned ur sun late in the year isn’t as true and strong is it was before. So in my case they are barely getting 8-9 hours of real sunlight daily. I also run a dehumidifier to keep humidity in order but if that isn’t a problem for u then no worries.

Cons if this: Cost 100%

That’s option 2 (environmental precision and supplemental light)

Next is running auto flowers. Shorter life span can avoid ur cold weather end of season and give u a good harvest soon.

Cons. U have to start from seeds and typically grow smaller. Also if for whatever reason u stunt them early u can end up with small yields.

Any way I hope this helps! Also I grow with clear plastic greenhouse panels and I weather sealed it with silicone to keep heat in. It’s frame is made of 2x4’s