Short answer. Snip the main stem's growing tip just above a node once the plant has 4–6 nodes and is growing vigorously. The two side shoots at that node become co-dominant, and lower branches catch up, giving a flatter canopy with more tops at similar height. Let the plant recover 5–10 days before flipping to flower. In a controlled trial on large greenhouse plants, pruning twice (at transplant, leaving six main branches, and again at the switch to short days) was the only architecture treatment that increased flower yield per plant over the control; cannabinoid yield rose too (e.g. CBDA 22.5 g vs 14.1 g per plant) [1].
What's happening
The apical tip makes auxin that flows down the stem and suppresses side buds (apical dominance). Remove the tip and the suppression lifts; the nearest buds grow out. An even canopy also matters because light falls off with depth, and yield follows light [3]; lower, shaded buds in cannabis have lower cannabinoid concentration [1].
How to do it
- Plant healthy, well rooted, 4–6 nodes (or 3–4 weeks from seed).
- Use clean, sharp scissors (wipe with 70 % alcohol).
- Cut the main stem 3–5 mm (⅛–¼ in) above the chosen node, leaving both side shoots intact.
- Optional: top again on each new main shoot after 2–3 new nodes (gives 4, 8, …).
- Combine with LST to spread new tops apart.
Numbers that matter
| Item | Typical | Notes |
|---|---|---|
| First top | 4–6 nodes | Earlier tops on weak seedlings stall growth |
| Recovery | 3–7 days before visible regrowth | |
| Last top before flip | ≥ 7–10 days before 12/12 | Avoid topping in flower; costs yield time (Grower practice) |
| Autoflowers | Don't top; use LST | Topping never produces what proper LST does on an auto, and it costs recovery time on a fixed clock (house position, Grower practice) |
How to confirm it worked
Within a week two (or more) shoots at the cut node are growing at equal speed; by flip the tops sit within ~10–15 cm (4–6 in) of each other.
Common mistakes
- Topping a stressed, root-bound or sick plant.
- Cutting below the node (removes the side shoots you wanted).
- Topping in flower.
- Topping autoflowers. Use LST instead.
- Topping, then leaving the canopy uneven with no LST.
Evidence
Apical dominance is Established plant physiology. Yield increase from double pruning is Supported by one controlled study on large (~2.5 m) greenhouse plants of a CBD-dominant medical cultivar [1]; small indoor plants and high-THC cultivars may respond differently. Topping vs not topping at commercial densities shows that density and architecture interact [2].
