The height of the plant is dictated by a lot of things but where you top generally isn't one of them.
Every time you top you double the number of "main" bud sites on that stem. Every "main" bud stem you create will also spawn a number of "sub" bud sites along each main stem.
When you top any stem, it will immediately stop any further growth along that particular stem and you'll get a "Y" split with 2 "weaker/smaller" "main" stems. Probably best I draw a very rough diagram as this took me a while to learn for some reason.
I'm only really showing one side of this but you'd be looking to do the same on both sides.
What I'm showing here is a plant that's had its first top at node 3.
This creates 2 "main" stems at Node 3 and you get no further nodes off the primary rooted stem from the pot. This gives you two, new "main" stems numbered 5 and 6. If you stop there, those two stems will keep growing and will eventually lead to two "main" bud sites/flower heads at their tip. Side shoots from those two main stems will form along the entire length of the stems (I've labeled only 6a and 6b but you will get far more than two sets of these side shoots from each "main" stem and every one of those will keep growing and will also eventually form bud sites/flower heads of their own).
If you decide to top again (you can do this on any node of stem 6 so you might want to do it immediately after 6a/b and turn those two into the new main stems or you might want to do it at Node 2 of Stem 6 as I've shown and leave stems 6a and 6b as sub stems of 6), stem 6 will NOT create a primary bud site/flower head and will instead split into "main" stems 7 and 8. In exactly the same way as stem 6, you can leave these two new "main" stems to keep growing and they will each eventually form their own bud sites/flower heads. Likewise they will also create their own side shoots (7a/b and 8a/b) that will likewise go on to create their own bud sites/flower heads.
If you decide to top yet again (this will be your 3rd top), stems 7 and 8 will NOT create a primary bud site/flower head and will instead again split into "main" stems 9-12. In exactly the same way as stem 6 and then 7 and 8, you can leave these two new "main" stems to keep growing and they will all each eventually form their own bud sites/flower heads. Likewise they will also create their own side shoots (I've not labelled them but you get the idea) that will likewise go on to create their own bud sites/flower heads.
For nodes 1 and 2 you can do the exact same things (except top the main stem of course) but you can safely top
SO
If you're still with me so far most peoples thoughts are by now "Yay more bud sites = more bud = bigger yield" and they'd be right, to a point. The problem is that ever time you top it causes multiple "problems".
- The topping is a high stress method so it impacts on the plants growth that generally required 5days or so extra growth time to make up for it
- Every time you split it makes the subsequent split stems weaker and thinner meaning your plant is in danger of snapping and breaking under the weight and you get a lot of small bugs instead of fewer larger ones
- It means you have to do a lot more defoliation and management including heavy LST as the plant gets very crowded meaning you're more prone to rot from additional humidity and lack of airflow
- The plants become too big for your grow space (a single heavily topped LST'd photo will EASILY fill a 80*80 tent and I speak from experience)
When you top/lst you're trying to hit a delicate balance of size, time, airflow, strength and manageability. Get it right and you can achieve monstrous yields with both photo's and auto's alike. Get it wrong and you get a mess of a plant that you can't control, is too big for your space, creates massive humidity and lighting problems and just turns into a disaster.
So what to do?
Many people wait to top until nodes 4, 5 or 6 of the primary stem and then cut off at least some, if not all of the nodes below. Personally I think topping at node 4, trimming off nodes 1 and 2 and leaving 3 to grow naturally (with maybe a single top) is the way to go. I think it was V8 or Citydweller who got me onto the 18-20 node grow and it was certainly excellent for my Dankberry.
The idea is
You get rid of nodes 1 and 2 off the main central stem.
You top at node 4 giving 2 stems. You top those again to create 4 stems.You top them AGAIN to create 8 total all branching back to node 4 of your main central stem.
At the same time, you top the two stems that are still at node 3 of the main stem at their node 2 to give 4. You top again to give you 8. You leave the two stems either side at node 1 of these stems giving you a further 2.
In total, that gives you 16 "primary" stems and the four "sub" stems from the node 3 branches. Everything else you defoliate and don't allow ANY other minor stems from growing. My Dankberry diary shows a half arsed attempt at this (I messed it up a bit but it was about 18 primary bud sites in all)
With auto's you are on a clock so this changes things. You don't have time to wait 3 weeks for the plant to recover from the 3 sets of toppings which is why 2 toppings is pretty much the limit for an auto because you can't stop it going into flower AND you don't get it growing for enough time in veg to thicken out and get big enough. You could probably do it (and some might have) but personally I'd stop at 2 at most.
Hope that makes some sense!
MJ
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