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The Weakest Links: Why Cannabis Growers Should Be Culling Their Weaker Plants

By Stephen Keen | Last updated: May 11, 2021
Key Takeaways

Focus on the best and forget the rest. To build a strong crop of healthy plants, don’t be afraid to cull the weakest plants at each stage. It’s how Mother Nature does it. Here's why culling at each stage will provide benefits in the long run.

This concept is going to sound backwards to many of you, but our years of cannabis growing experience have shown that the best way to produce the highest quality product is to cull plants at each stage of growth.

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Professional gardeners know this rule well, but most cannabis growers do not. In fact, it seems backwards to many cannabis gardeners to throw out plants at the transitions between the different stages of a plant’s life cycle (clone/seedling, vegetative, and flowering) as they have put effort in keeping these plants alive and as healthy as possible.

However, culling plants at each stage will produce a more robust and higher yielding crop through the selection of the strongest individuals and the discarding of weak plants.

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The Logic Behind Plant Culling

As plants grow, their true character comes out. Plant growth characteristics can be delineated as sensitive to low, medium, or high amounts of dissolved solids in water; preference for direct or indirect light; susceptibility or resistance to disease and pests; short or long internode length; and so on.

Some are large growers, some are not. Some are prone to bugs and infections, while others are heartier. Some can thrive on limited nutrients and others need to be pampered to reach their full potential.

These differences cannot be seen simply by looking at a seed or clone cutting. Instead, they only show up once the plants have a chance to grow and are exposed to your individual growing style and cultivation environment.

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As such, it is recommended to cull plants at each stage before moving them into the next phase. This means that you survey your crop, select the best ones to move on, and destroy the rest.

Let’s repeat that: At each stage of the grow, throw some plants away and keep only the best performers.

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To make this work, culling losses must be factored in from the beginning. For example, let’s take a conservative estimate of 10 per cent culling loss at three stages; clones, rooted clones, and vegetative growth.

Using this formula requires about 140 initial cuttings for every 100 plants that end up in the flower room. This culling loss can (and should) be adjusted based on your success rate and cultivation style. When losses are not factored in from the start, the pressure to produce often overrides plant quality.

Gaps in your healthy plant count are filled with less than desirable replacements, which in turn bring yield potential down and increase the potential for pest/disease incursion, both of which create more work for facility personnel.

The Rewards of Culling Plants

With culling, the plants that make it through to harvest will be the best performers. You won’t be struggling with underperforming plants or playing catch-up.

The culling process can help avoid many common cultivation setbacks associated with pests, disease, and genetic drift, since sickly plants are often the most vulnerable.

The plants selected in this process will produce higher yields and better-looking products. You will easily be able to make up the cost of starting extra plants through the quality of the ones that make it to flowering.

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Written by Stephen Keen

Profile Picture of Stephen Keen

Stephen Keen has been an indoor gardening hobbyist for more than 10 years. His personal successes with his garden led him to want to bring new ideas, mainly water-cooling, to the mainstream.

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