What is Screen of Green?
ScrOG is an abbreviation of Screen of Green, and it is one of the most productive, energy efficient and easiest ways to grow indoors.
As the name implies, the ScrOG method adds the use of a screen to the Sea of Green (SOG) method. The screen can be chicken wire or some other material, just make sure it's sturdy enough to hold back the growing canopy, and the holes should have a diameter of about 5 cm, so that the plant can easily grow through it and be supported by it.
The screen is suspended between the grow medium and the lamp. You let the plants grow through the screen and when the are 7.5 - 10 cm above the wire, pull them back under and spread them out where you want them to grow (where they get the best lighting).
The screen should be cut to size, relative to the size of your lamp. Here are some examples:
150hps: 55 x 55 cm
250hps: 68 x 68 cm
400hps: 89 x 89 cm
600hps: 105 x 105 cm
1000hps: 137 x 137 cm
Where you place the screen depends on the heat and size of your lamp. If your lamp is air cooled, you can keep the distance between screen and lamp smaller. The closer the distance between the lamp and canopy the better, but the lamp should of course not scorch the buds. A simple fan blowing between the canopy and the lamp may help. Here are some guidelines for the distance between the lamp and screen:
150hps: 25-30 cm
250hps: 30-38 cm
400hps: 40-51 cm
600hps: 51 cm or more
1000hps: 61 cm or more
The general rule is that you place one plant per 30 cm2 of screen. If uncertain, place fewer rather than more plants.
The space between the plant medium and the screen needs to be large enough for you to manipulate the plants during the training phase. Approximately 20 cm is a good guideline. You can suspend the screen with some wood and a couple of screws (be creative!).
All strains can be grown using the ScrOG method, although some require more training than others. Heavy yield indica's are very good, but with proper training and timing unruly sativas can also do very well.
Having knowlege of how much your strain stretches is helpful when determining when to switch to flowering. For example: If one had a very stretchy sativa. You would want to start flowering her with much less of the screen filled. Just the opposite for a nice stunted indica.
As mentioned above, when the plants have grown 7.5 to 10 cm through the screen it's time to pull them back through the fence. Reach under the screen and pull the branch back, then place it where you want it to be. Feel free to use plastic twisty ties. Try to situate your main branches towards the barest parts of your screen. They will branch out the most and usually yield massive buds. Remember there's going to be a lot more branching when flowering kicks in. Smaller buds that are now exposed to more light will grow upwards toward the screen.
ScrOG is not natural for cannabis plants, as there's not enough space for all the leaves. So some leaf trimming is quite desirable. If a leaf gets in the way of light for a bud site it needs to be removed. Don't overdo it though. Trimming continues into flowering, ending during the later stages of flowering.
If you induce flowering too early, you will have a much smaller yield. However, if you wait too long, the same may happen. An overcrowed canopy is not what you want. Remember: the plants you start to flower are probably going to double in size.
So, you have turned back the timer to 12/12 and it has been 4 days now. You get in there and pull all the new shoots back under the screen and put them where you want them to be. A few more days pass. More growth. Now you have to make a decision: just how far over the screen do you want your buds to be? If you stop training them early in the stretch, they will grow a little above the screen (maybe 7.7 - 15 cm, depending on the strain). If you continue training them until they start to top out, they will grow only a little more and most of the bud will form right in the screen. It may take you a grow or two to get the timing down to where you want it to be.
Keep an eye out for mold and try to have as much air flow between the buds as possible. Air circulation becomes critical as the buds begin to form and things start to get packed in the box. 24 hours air movement is suggested 7 days a week. Better safe than sorry!
While manipulating the branches, invariably some will snap. Usually these branches will recover themselves if you leave them alone, although sometimes a little support will help. In many cases an explosion of growth will happen above the damaged area.
Once a few trimmings are done and all is set in place it's time to start thinning out your undergrowth. The undergrowth is an area that should be kept clear of dead leaves and you should also ensure that proper ventilation can get through the canopy via the undergrowth. Trim all remaining sprouts left on the stems and most of the other undergrowth. This will help the plant direct more energy towards the larger buds instead of wasting energy on the smaller ones.
The canopy does not have to be perfectly even, just close, so that light will be distributed evenly. Treat the buds as if it's a field rather than a forest (as in the SOG method). Do not allow dominant buds to overtake the canopy. Bring them down to size with the rest.
Good luck and a bountiful harvest!
Based on the ScrOG method as described by greenmonster714 on the GrassCity forum