Should I top, train, or defoliate — and when?

The short answer

• All of it is aimed at one thing: an even canopy where the light lands on many bud sites instead of one tall top. Pick the method by how much you want to cut.
• Top early and small — when the main stem is 10–15 cm with at least two pairs of full leaves — and stop topping and heavy training around the flip, because the plant is about to stretch.
• The stretch is the number that decides your veg time: reported as anywhere from 25 % to more than 600 % of height at the flip, depending on the variety. Measure yours once and you never guess again.
• Do not defoliate in the first three weeks of flower. Remove leaves that shade bud sites or trap humidity; do not strip the plant. The evidence for aggressive schedules is thin, and the chapter says so.

What training is for

A cannabis plant left alone grows one dominant top and a Christmas-tree shape, and most of its leaves end up shading each other. The point of every training method is to flatten that into a canopy that intercepts the light you are paying for and puts it on flowers. The reference chapter frames it with a number, leaf area index — square metres of leaf per square metre of floor — and suggests filling the space to about 1.5–2 as fast as possible in veg, then holding around 2.5–4 through early and mid flower. Below that you are lighting the floor; above it, leaves shade leaves and the interior stops moving air, which is where mould starts. You do not need to measure it. You need to know that “more leaves” stops helping surprisingly early.

The methods, in order of how much you cut

• Bending and tying (low-stress training). Pull branches down and outward and tie them so the side shoots grow up level with the top. No cut, no recovery pause. The gentlest way to a flat canopy.
• A screen (SCROG). A net — the chapter gives 7–15 cm mesh — over the canopy; growth is woven through it to hold the top flat. Bending with a structure.
• Topping. Cut the growing tip off so the plant sends energy into two side branches instead of one leader. The chapter’s only concrete procedure is written for building a mother plant, and it is the right shape for a home grower too: top when the main stem is 10–15 cm tall and has at least two pairs of fully expanded leaves, leaving the two nodes below the cut; remove any shoots lower than that; when those two shoots have grown a little past the nodes beside them, top each of them — four growing points; repeat once more if you want eight. That gives you an even multi-top plant in a few weeks.
• Staking. Not a training method so much as a promise to your later self that the colas will not fall over.

One thing the chapter says that runs against most online advice: in a dense commercial canopy the authors recommend avoiding topping, because it costs height and favours lateral growth that the density does not need. A home tent with a few plants is the low-density case where topping is normal. That reading — that your tent counts as low density — is ours; the density line is theirs.

The stretch, and why it decides your veg time

When a photoperiod plant is switched to 12/12 it does not start flowering immediately; it keeps growing upward for a while first. The chapter reports that growth as 25 % to more than 600 % of the plant’s height at the flip, depending on the variety. That range is the whole reason “how long should I veg?” has no general answer: the same four weeks of veg finishes at very different heights in different plants.

The chapter’s method is short and worth adopting: measure the plant from the medium to the top node on the day you flip, and again when it stops gaining height, which is usually about 30 days into flower. The ratio is that variety’s stretch in your setup. Next time, veg for as many days as gets you to the flip height that, multiplied by the stretch, fits your tent. Two grows and you have a number nobody on a forum can give you. The chapter also notes that beyond about 30 days of veg plants generally get too large to keep a uniform canopy in a controlled space.

And the rule that follows from the stretch: stop topping and heavy bending at the flip. The plant is about to put on most of its height and structure; damage during that window costs yield, and there is nothing to gain by shaping a plant that is about to reshape itself.

Defoliation: the trade, and the timing

Leaves are the plant’s sugar factories. Removing one is a trade — better light and air into the canopy against less capacity to make the sugar the flowers are built from. The chapter’s guidance on timing is specific enough to follow:

• Not in roughly the first three weeks after the flip. The plant is establishing its flowering structure and needs the factories.
• Selective, not wholesale. Take the leaves that shade a bud site or sit inside a dense canopy trapping humidity. Leave the rest.
• A light pass 5–15 days before harvest is a recognised practice to open the canopy for the finish.

The aggressive schedules you will find online — strip the plant on day 21, again on day 42 — are practitioner opinion. The chapter’s own words on pruning cannabis are that its effects are not well studied and that much of the published guidance is experience rather than trial data. That is not a reason to do nothing; it is a reason to do the conservative version and judge by your own result.

How to check this yourself

• Measure height at the flip and at day 30. Write both down with the variety. That ratio is worth more than any forum answer.
• Look down at the canopy from above under the light. If you can see floor, you have room to train outward. If you cannot see any lower leaves, the canopy is past the point where more leaf helps.
• Before removing a leaf, ask what it is doing. Shading a bud site or trapping humidity: take it. Just being a big leaf: leave it.
• After topping, count growing points in a week. Two, then four. If a topped plant sits still for ten days it was topped too young or too hard.

What would show that we have this wrong

If your plants are packed at commercial density, the chapter’s advice is not to top at all, and the bending methods matter less because the plants shape each other. And if a variety’s stretch measures under 50 % in your setup, you can veg longer than this page implies — that is the point of measuring it rather than reading about it.

Where our device fits, stated narrowly

Croplock does not train plants or tell you when to cut. It keeps the run’s phase and day count, so “are we inside the three-week window after the flip?” is a fact on the screen rather than a count back through a notebook, and the hourly canopy photos give you a dated before-and-after for any cut you make. Height is not something it measures; the two numbers above are yours to write down.

Sources

• Matzneller, P., Gutierrez, C. & Caplan, D. “Canopy Management.” Ch. 7 in Cannabis in Controlled Environment Production (CRC Press). DOI 10.1201/9781003150442 — the training taxonomy, the topping procedure, the stretch range and measurement method, the de-leafing timing, the leaf-area-index targets, and the caveat on the evidence base. Restated in our own words throughout; the LAI targets are the authors’ experience and are given as such.
• The judgement that a home tent is the low-density case is ours.

More of these at Answers. The device is at croplock.com.

Related: Why hasn’t it started flowering? — the flip and what follows it. How much light does it need? — the light the canopy is being shaped to catch.

Also read: Curling leaves: heat or hunger?