Contrary to popular belief you should be running higher nutrient concentrations in winter than in summer. The reason is simple: less evaporation. Plants will take up what they can via three pathways: transpiration, ATP (active transport) and reverse osmosis at the root level. You are growing in what looks to be a coco/perlite mix and I assume hand-watering. If I'm wrong, then sorry I missed it.
So you'll have less evaporation in the pot and less water loss through transpiration. Less transpiration will affect mainly magnesium uptake, followed by calcium. Increasing nitrogen levels can help uptake magnesium and calcium, but can also result in raising pH at the root zone which will start to lock out iron and zinc. A good chelated micronutrient mix that includes magnesium, iron, zinc and other micronutrients can help when temperatures drop, but your first line of defence is to actually increase balanced nutrient concentrations. Also, don't forget to flush regularly to prevent excess salt build-up, but take into account the reduced evaporation at the root zone. You shouldn't have too many problems with a perlite mix that drains well, even in winter.
Studies have shown the ideal difference between dark and light temperatures is 15C, so in many cases it may be preferable to have your lights on during the day in winter if it gets cold in your area.
In addition to reduced transpiration lower temperatures will obviously affect metabolic rate. Pretty much everything on earth slows growth when it gets cold for this reason. You can offset the loss of temperature transpiration somewhat with a fan blowing on the leaves (more wind evaporation, not cooling).
Another tip, if you are hand-watering into coco-perlite, you will see much faster growth with an automatic watering regime. If you're already doing that, try increasing the number of times you water but reducing the amount you water each time. A bit like drip feed. And if you autowater, you can then add an aquarium heater to your reservoir and that will make a big difference to plant metabolism in winter.
One final trick: vent your room/tent out the bottom so that the extractor fan pulls hot air rising off the heatsink down through the canopy and out the bottom of the grow area.
That's all I've got because frankly, I live in Australia and it doesn't get that cold.
Heya Mate!
Thanks for the great post. Just the type of info I love getting.
Actually growing in pro mix HP, so 70% peat moss, 30% perlite. Whats interesting about this run is I have 12 LGB clone, and have them in groups of 3. I put 4 into NEW promix, 4 into recycled/re used pro mix, and 4 into a recycled mix that has some organics in it. Then within each group of 4, one I feed every watering at 700ppm, the other 3 at 600ppm, out of those, one I have also added 20% EWC into the soil mix, and another I feed compost teas 2x during veg.
My tap water ppm is 210ppm. I PH it to 6, and it drifts up a couple points thereafter which Im ok with. My run off is 6.4 consistently. I currently use remo nutrients. Canadian brand.
I also measure the runoff of each plant after every watering, about a cup of run off. I then track these numbers to see if there is any buildup or reduction or staying equal. Organics really skew the numbers, so I just keep a watch in which direction the number is going to see if there is a reduction in ppms, or a buildup. I really should just be doing hydro, Im a meticulous numbers guy!
A few things I have learned is that all plants look equally happy across the board. The plants with higher ppms aren't doing better in any regards to my current problems. Since I have so many variables and I am getting similar issues, I would be inclined that my issue is not related to anything nutrient/ph related.
I do have a fan on them, 16" Hurricane, using 43 Watts, on the lowest setting, oscillating. It moves all leaves pretty hard. I wouldn't want it to be any harder than currently. It moves air around the room so well, that when I moved my exhaust from the ground to higher up, the overall room temps did not change at all. But I will keep that in mind for when I build a room in the future.
For autowatering, I would love to automate this. I actually have a disability so daily labour is becoming not fun. Problem is I have hardwood floors here and don't want the risk of any overflows. I know I can get large res trays etc, but I want to leave that for my new purpose built room. Im shutting down in a year here, and starting up in a new home.
Cheers!