Short answer
Topping is cutting the growing tip off the main stem of a cannabis plant. The cut removes the apical bud, and the two shoots sitting at the node below take over as new leaders. Do it during vegetative growth, after the plant has at least four nodes, and give it three to five days to recover before you touch it again.
Prerequisites
- A plant in vegetative growth with at least four to six nodes
- Sharp scissors or pruning snips
- Isopropyl alcohol at 70 percent or higher
- Two to three weeks of grow time before you plan to flip to flower
How to top a cannabis plant
- Wipe the blades with isopropyl alcohol and let them air dry.
- Count up from the base and pick the node where you want the plant to split. Leave at least three full nodes below that point.
- Cut the stem just above that node, leaving about a quarter inch of stem above it.
- Remove the severed tip from the grow area.
- Leave the plant alone. No training, no defoliation, no transplant for three to five days.
- Water as normal and keep the light at the same distance while the two new leaders stretch.
- Wait until each new leader has two or three nodes of its own, then top each one if you want a wider canopy.
- Stop topping two to three weeks before you switch the light cycle to flowering.
What happens after the cut
The shoot tip produces auxin, a hormone that travels down the stem and holds the buds below it in check. That effect is called apical dominance. Cut the tip and the auxin supply from above drops, so the buds at the node underneath push out. You get two tops instead of one, and the canopy starts to spread instead of stretching up in a single column.
When not to top
- Autoflowering plants. Their vegetative window is short, and the recovery time eats into it.
- Plants already in flower. New leaders will not have time to fill out.
- Plants that are sick, root bound, or recovering from transplant.
- Seedlings under three nodes. There is not enough leaf area to fuel the rebound.
Topping compared with FIMing and low stress training
Topping removes the tip and gives you two clean leaders. FIMing cuts part of the tip and can produce three or four, but the result is less predictable. Low stress training bends stems without cutting anything, which keeps the plant unstressed but takes longer to change the shape. Many growers combine all three over a single vegetative run.
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Topping hemp grown for CBD
Hemp grown for CBD is the same species, so the plant responds the same way. A topped hemp plant carries more flower sites, and the female inflorescences are where CBD and the other cannabinoids build up. More sites on a healthy plant means more material at harvest. The tradeoff is the same as with any cannabis plant: recovery time, and a need for even light across a wider canopy.
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Common mistakes
- Cutting too low and stripping nodes you meant to keep.
- Topping again before the first cut has healed.
- Topping and transplanting on the same day.
- Using dull blades that crush the stem instead of slicing it.