SOP: To top or not to top

Download the to top or not to top SOP checklist A step-by-step checklist to help you decide if you should top or not.

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Purpose

Decide whether topping is the right move for a specific cultivar in a specific room, based on canopy goals, labour cost, veg time, plant density, and likely impact on uniformity and crop execution.

Core principle

Topping is not a default. It is a tool.

It can help reduce height and improve branch balance and canopy uniformity in some cultivars, but it also adds labour, recovery time, and another wound site. Research and commercial cultivation guidance both support treating topping as a cultivar- and system-dependent choice, not a universal best practice.

Step 1: Define the problem you are trying to solve

Before deciding anything, answer this:

What problem is topping supposed to solve?

Valid reasons include:

• Excessive vertical stretch

• Poor canopy uniformity

• Weak lateral development

• Difficulty keeping tops in the productive light zone

• Need for a more balanced branch structure

• Need to reduce plant count while maintaining canopy fill

Topping is more defensible when it solves one of those problems. If there is no clear problem, it is probably being done by habit. Topping is known to reduce plant height and can promote more equally long branches, which is why it is often used for canopy control indoors.

Step 2: Assess cultivar architecture

Ask these questions about the cultivar:

• Is it strongly apically dominant?

• Does it stretch aggressively?

• Does it naturally throw strong laterals?

• Does it build a narrow Christmas-tree shape, or a broad, balanced structure?

• Does it recover quickly from stress in veg? Has it shown awkward regrowth or uneven post-top response before?

General rule:

• Apically dominant, high-stretch cultivars are more likely to benefit from topping.

• Basal-dominant or naturally branching cultivars may not need topping at all.

Commercial genetics guidance specifically recommends evaluating cultivar growth pattern and response rather than treating topping as standard practice across every genotype.

Step 3: Assess room and production model

Now ask whether topping fits the facility, not just the plant.

Top if the room benefits from:

• Tighter height control

• More balanced branch structure

• More even canopy under fixed lighting

• Fewer plants to hit canopy coverage

• More uniform crop expression across the canopy

Avoid topping if the room depends on:

• Shortest possible veg time

• Lowest labour input

• Minimal crop interruption

• Reduced wound risk

• Simple, repeatable workflow across many plants

Commercial cultivation guidance notes that topping can improve canopy and test uniformity in some scenarios, while non-topping may offer faster veg, less labour, and fewer disease or viroid entry points.

Step 4: Check plant density strategy

Do not decide on topping in isolation.

Ask:

• Are you running high plant count and shorter veg?

• Or lower plant count and longer veg?

• Are you trying to fill space with fewer, wider plants?

• Is your canopy model built around vertical tops or broader lateral spread?

Plant architecture and planting density interact. Research in pharmaceutical cannabis found higher density increased yield per area but reduced cannabinoid uniformity across the plant, and plant architecture manipulation changed how density affected crop outcomes.

Practical takeaway:

• If your strategy depends on fewer plants covering more width, topping may help.

• If your strategy depends on higher density and fast turnover, topping may add more cost than value.

Step 5: Estimate the operational cost

Before topping, confirm the room can absorb the cost.

Ask:

• Can the schedule absorb extra veg time?

• Can the team execute topping cleanly and consistently?

• Will the added labour pay back in canopy quality or yield?

• Are sanitation standards good enough to justify another cutting event?

Commercial cultivation guidance notes topping can create a growth pause, increase labor, and create a wound entry point for disease or viroid transmission, especially if sanitation is weak.

If the team is rushed, sanitation is inconsistent, or veg time is tight, topping becomes less attractive.

Step 6: Make the decision with this rule

Use this rule:

Top only if it improves canopy control or plant architecture enough to justify the extra work, time, and risk.

That is the decision standard.

Not:

• because everyone does it

• because the previous cultivar needed it

• because it is “what commercial growers do”

Step 7: If topping, execute intentionally

If the answer is yes, define the topping protocol clearly.

Record:

• Cultivar

• Date of topping

• Plant age / node stage

• Target branch structure after topping

• Expected recovery window

• Expected impact on height and width

• Sanitation method used

• Who performed the task

Topping affects morphology and can change height, branching, and within-plant uniformity, so documenting timing and response is important if you want repeatable decisions later.

Step 8: If not topping, define the alternative

If the answer is no, the decision still needs a plan.

Record what will replace topping:

• Higher plant count?

• Longer veg?

• Wider spacing?

• Trellis strategy?

• Different pruning approach?

• Cultivar-specific canopy target?

This matters because “don’t top” is not a strategy by itself. It only works when the room has another way to hit canopy shape and fill goals.

Step 9: Review after the run

After harvest, score the decision.

Review:

• Canopy uniformity

• Height control

• Labour spent

• Veg duration

• Ease of room execution

• Consistency of top development

• Test uniformity, if tracked

• Yield per area, not just per plant

• Whether the cultivar fits the chosen method

This matters because published work shows pruning and density choices can affect not just architecture but also within-plant uniformity and yield distribution.

Fast decision checklist

Use this quick version in the grow room.

Top if:

• The cultivar is strongly apical

• Stretch is hard to control

• Canopy uniformity is a priority

• Fewer plants must fill the space

• The room can afford more labour and veg time

• Sanitation is strong

• Previous runs showed topping improved structure

Do not top if:

• The cultivar already branches well

• Height is manageable without it

• The room depends on fast veg turnover

• Labour is tight

• Sanitation is inconsistent

• The added cut creates more problems than it solves

Plant count and spacing already solve canopy fill

Download the to top or not to top SOP checklist A step-by-step checklist to help you decide if you should top or not.

Download now