My last grow (5x Dinafem Cheese XXL) I ran 24/0 for the first few weeks, then 18/6 from week 3 onwards and had great results, but was constantly battling the damn humidity spike at lights out. I've got good tent ventilation but ambient humidity here is naturally high so faster air exchange doesn't always reduce humidity, in fact it often brings in cold, damp air and raises RH even higher. I luckily didn't have any mold in the end, but it was a constant worry seeing the RH spike up to the 70's in late flower.
This time I thought I'd try a 24/0 cycle throughout in order to keep the environment under control and avoid that RH spike. I've got 2x mephisto sour livers and 2x DP auto cinderella jack growing in a 4x4 under a Mars TS 3000 LED (450w). I'm up to week 5 and while it's been mostly fine (aside from one plant with serious N tox from the biotabs) but overall the plants have been looking a bit ragged and worse for wear.
Decided to switch to 18/6 yesterday, and WOW.
The difference in the plant health and wellbeing in ONE day is unbelievable! Before the dark period they were growing OK, but they were a bit bunched up, hunched over and flaccid, struggling to stretch or recover quickly from the LST. Now the leaves and stems are standing strong, praying up to the light, all the bud sites have separated out and found their own spot in the canopy, they've stretched twice as far in one day with a dark period than they usually do. This is true of every single plant in the tent, both strains.
I'm sold. A dark period DEFINATELY seems to make a very noticeable difference. Ironically, after doing all this I remembered that I tried switching to 24/0 to control the RH spike on my last grow too, but the plants looked a bit sad after a few days of 24hr light, so I cut it back down.
So... that is three different strains, all respected breeders, all clearly preferring a dark period in my setup. I'm sure this could vary depending on light type/strength, but I'm definitely staying away from 24/0 going forward.
