Ok so im writing this to help out anyone who wants to or does grow 12/12 from seed. You can use this method of growing to try new strains, pick good mums or dads, have 2 oz of many strains instead of 18 of 1.
Ok so my first point is with this style of growing the plants will flower when they reach a certain age, not size or anything else. So with this in mind you normally have 3-4 weeks to grow the biggest plant you can, every now and again you get a 5 or 6 weeker these end up being huge.
There are a few things that you can do to get the biggest plant you can in that short time:
DONT pot up, start them in between 6.5-11L pots any more is a waste and I have seen no noticable yield difference between the 2 sizes often my highest yielder is in the smaller pot. advantage for bigger pot though is watering every other day instead of every day. But I also like watering every day as i can change my feeds very fast to resolve any problems.
Use a good soil mix with perlite and some bat guana if you can, root castings and seaweed would go a miss but I normally dont bother. When i add the guana i add half the amount around 3" from the bottom of the pot then mix the other half in with the soil that goes on top, that way the roots go down toward the bottom normally so when the tap root does that it will hit gold and sread out around this very fast.
DONT overwater your plant, the major reason most growers pot up. When the plant is young it will drink fuck all, so after you have watered it in then leave it for around a week (this will vary depending on many things in your room) but let the pot dry right out before they get watered again and then they will explode with growth. This works as the plant will use alot of its energy to makes roots in the first week or 2, so make it search for water and gets its roots all around the pot then when you water it next it can take up so much food.
Get your light close, fuck this give little ones less lumens, all they need is not to fry. Do the back of the hand test, if you feel any heat from the bulb move it up 2" above the tops of the seedlings and they will grow into it. Just keep them away from any heat for 2 weeks but as close as you can to the light without them getting any heat. DONT put the bulb 2 ft away and let them grow into it as then you will end up with 1ft plants, i have done this to test the age or size theory to see why or how they flower.
I normally do 9 differnt strains under a 400w and aim for 2oz a plant. This way i have a nice selection to smoke every 100 days and any keepers get cloned when they get lollipopped. There is no need to train your plants if growing this way, other than maybe lst, but suppercropping and topping majorly hurt your yield as the plant doesnt have the time to recover before flowering and again ends up being really small. If done right 12/12 plants normally end up around 3-4 foot although in my last diary i have a 6ft beast.
Try and run a humidity of between 60-80% when they are vegging as this makes the fan leaves much larger as they cant transpire water as well but as they get bigger they take in more energy as a result.
Get a fan blowing them from day one to make them root faster and make a hardier stem, this will save you alot of string being used to hold branches, although some will still have to be used as the plants havent vegged for long and therefore dont have very thick stems. That being said ive has stems as fat as my finger with no veg.
The usual things also apply like dont overwater your plants as it will majorly stall them.
Have a very good air flow as it aids plant growth.
Keep your room pest free.
remove any leaves over 50% damaged.
Make sure your day/night temp swing is under 5C for b est results but the closer the better. This minamalises strech in your plants.
I cant think of anything else now but 12/12 growing is a great method for all growers, simple yet effective. You can aim for 1-1.5gpw if this method of growing is done right. My gpw is always better if i do this methods with a 400 than a 600w. The 600w is normally nearer the 1 and the 400 nearer the 1.5
Hope this helps someone