How Do You Prune Marijuana Plants

(Q) I've tried to read everything on pruning and I still don't get it.  My plants are almost a month old, have three and four sets of leaves and seem very healthy.
(A) First off, you might not have to prune them. Second, leaves are not usually the purpose or the target of pruning. Third, knowing why you prune, and what happens when you do so will probably answer all the rest of the questions.

You Prune For Two Reasons:

1) To control the upward or outward growth of your plants.  In other words to keep them short.
2) To promote node sites (or bud sites).  In other words to create more branches (growing tips).

When you look at the mainstem of the plant and how the leaves grow from it, you will find it will be identical to any branch that grows from it, or any branches that grow from them, etc. So any reference I make to the mainstem here, holds true for any branches, or any branches that grow from those branches, etc. The point at where a leaf joins the mainstem (or branch) is the node, at the node and just above the leafs' stem (petiole) you will find a **bud**. This bud will become a branch.  Under the right conditions branches will grow.  Now, keep in mind that some varieties of plants are good branchers, some are not. Now let's assume the reason we're pruning is #2 above, to promote node sites or branching.  If you cut the top of the mainstem off then look at the plant, there will be some leaves and associated nodes. Since the top of the plant is gone, the growth energy that would go there is now going to the remaining nodes because it has nowhere else to go. What you did by topping the plants was to FORCE growth at the nodes thus promoting branching.  The nodes nearest the light will grow the fastest.  You would do this if you don't want a plant to grow too tall, but would rather want it to grow out. If this is your first crop you'll understand much better what you want once you've watched a plant through its entire life cycle. If you topped the plant for reason #1, all the above would still occur as a by-product, and most likely you would have to deal with the top branches eventually becoming too tall.

(Q) Where exactly do I make the cuts?
(A) Appx 1/4 to 1/2 inch above the node that will remain on the plant.

For cutting off leaves, cut them midway on the petiole.

(Q) Which set of leaves do I cut?
(A) You don't cut leaves off, you're just using the leaves as an easy way to identify the nodesites.  I believe every leaf feeds energy to its nodesite, cut off the leaf and the branch at that nodesite may not develop as expected.

(Q) And why am I cutting them?
(A) Usually you don't cut leaves off unless there dying, or you have a big fat juicy bud that's trying to grow underneath a big leaf.  If the bud would benefit from the light the leaf is shading, you decide which you'd rather have :-)

(Q) My logic would be the more leaves the better opportunity for photosynthesis.
(A) As long as the light can get to them. 

The only leaves that are going to use the light are the ones facing the light.  A few leaves deeper into the canopy and the extra leaves wont do you any good. HID lights penetrate deeper into the canopy than fluorescent. Side lit systems like the phototron require you to prune to promote branching * AND* to remove larger leaves that tend to grow nearest the lights in order for direct light to benefit the newer inner branches. The main reason this works in a phototron is the side lightings ability to get under leaves that want to grow horizontally.  Without removing leaves near the light the trons fluorescent wouldn't penetrate. Top lit systems depend on light penetration qualities of the lamp going through and around the leaf to do this. I'd say a top lit garden would have enough leaves (full canopy) when you don't see much light when looking up at the lights from the bottom of the canopy. A phototron is like a top lit garden only on its side and rolled up into a circle.  Its canopy are the sides of the unit. One thing about pruning to remember is that one thick stemmed shoot tip is being replaced by two or more much thinner shoot tips.  Buds may be more numerous but they will be smaller. A pruning rule of thumb: The thinner the shoots, the smaller the fruits.

(Q) I have seven plants and plenty of room .  Thanks in advance.
(A) As I said, you might not have to prune.

It wouldn't be a bad idea to do it on one plant just to get the experience.  Just be prepared for a shorter bushier plant than the rest. In the end you might find that 1 or 2 pruned plants can do as well as the 7 you have now.