Using garden soil in a bucket with no holesoverwaterring looks an issue too... looks like you need better drainage as well... from what I see there very little perlite in your mix. Unless im seeing it wrong
What are you using to aerate the soil?Using garden soil in a bucket with no holes
looked up smart pots and the size of tomato plants are 35% bigger in smart pots compared to plastics
Plant Containers: Plastic vs. Fabric
fifthseasongardening.com
Thank you very muchMy advice...
First... you need to add more Perlite to your soil mix...
Second... you can use a plastic container or bucket but you MUST BE SURE TO DRILL HOLES IN THE BOTTOM to allow run-off
Third... if you are keeping this plant outdoors in a shed and temperature is a problem then you should either bring it inside to warmer Temps overnight or at the very least figure out some kind of plan to insulate them in the shed if they are not able to be brought inside
Also how big is the shed that you're keeping it in? Maybe buying and running a larger HPS light setup like a 600w would warm the shed up enough to keep the temps at a good place. I have so many questions and those answers are all variables that play important roles in the growth of your plant....
Do you run your lights during the day and they are off at night? If thats the case... maybe run the lights so they come on during the nighttime to combat cold temps....