The Science Behind Topping by B.Real

b.real;1800169 said:

removing fan leaves is silly. it sets the plant back for sure. leaves are the powerhouse of creating glucose/startch via photosystems 1, 2 and the calvin cycle. on top of that, if the plant is hungry it can use the nutrients in the leaves as backup food! never remove fan leaves! it will also create buds that are very leafy in order to compensate for the missing fan leaves, especially when defoliation occurs in bloom!

pruning like lollipopping and topping on the other hand are different. removing flower sights promotes growth and energy to go to other flower sights.

here is what happens when you top:

"Plant physiologists have identified four different stages the plant goes through after the apex is removed (Stages I-IV). The four stages are referred to as
1.lateral bud formation,
2."imposition of inhibition" (apical dominance),
3.initiation of lateral bud outgrowth following decapitation, and
4.elongation and development of the lateral bud into a branch.

These stages can also be defined by the hormones that are regulating the process which are as follows: Stage I, cytokinin promoted, causing the lateral bud to form since cytokinin plays a role in cell division; Stage II, auxin is promoted, resulting in apical dominance ("imposition of inhibition"); Stage III, cytokinin released resulting in outward growth of the lateral bud; and Stage IV, auxin is decreased and gibberellic acid is promoted which results in cell division, enabling the bud or branch to continue outward growth.[1]

More simply stated, lateral bud formation is inhibited by the shoot apical meristem (SAM). The lateral bud primordium (from which the lateral bud develops) is located below SAM. The shoot tip rising from the SAM inhibits the growth of the lateral bud by repressing auxin. When the shoot is cut off, the lateral bud begins to lengthen which is mediated by a release of cytokinin. Once the apical dominance has been lifted from the plant, elongation and lateral growth is promoted and the lateral buds grow into new branches. When lateral bud formation prevents the plant from growing upward, it is undergoing lateral dominance. Often, lateral dominance can be triggered by decapitating the SAM or artificially decreasing the concentration of auxin in plant tissues."

Apical dominance[edit]

Apical dominance is phenomenon where one meristem prevents or inhibits the growth of other meristems. As a result the plant will have one clearly defined main trunk. For example, in trees, the tip of the main trunk bears the dominant meristem. Therefore, the tip of the trunk grows rapidly and is not shadowed by branches. If the dominant meristem is cut off, one or more branch tips will assume dominance. The branch will start growing faster and the new growth will be vertical. Over the years, the branch may begin to look more and more like an extension of the main trunk. Often several branches will exhibit this behaviour after the removal of apical meristem, leading to a bushy growth.

The mechanism of apical dominance is based on the plant hormone auxin. It is produced in the apical meristem and transported towards the roots in the cambium. If apical dominance is complete, it prevents any branches from forming as long as apical meristem is active. If the dominance is incomplete, side branches will develop.

Recent investigations into apical dominance and the control of branching have revealed a new plant hormone family termed strigolactones. These compounds were previously known to be involved in seed germination and communication with mycorrhizal fungi and are now shown to be involved in inhibition of branching.[13]"

basically plants have most of their auxins/hormones in their main shoot, to get taller becuase they need to compete for light with other plants around them. i always used to think that if you cut the top shoot, you would lose all those good hormones, but according to this info, the auxins get transfered to the terminal/side shoots! you have to top correctly though! if you fim, the auxins will get caught up at the top of the plant!

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