FIM pruning in cannabis plants (step by step)

There are many ways to train Cannabis plants during the vegetative stage of 18/6, and one of those is a technique called fimming.

This basic plant training method will encourage bushy and compact flowering plants, so in this article we give a guide to fimming Cannabis plants, how it works, a step by step guide to how to perform correctly, the benefits associated and mistakes to avoid.

Cannabis Plants and Apical Dominance Explained

Before we discuss about fimming Cannabis, it is important to understand the meaning of apical dominance.

This means a dominant central stem will grow and this is the case with Cannabis plants, due to a growth hormone named auxin. This is the same hormone that is responsible for vertical growth and how much the plants will stretch once the lights have been changed to 12/12.

There are other ways to disrupt the flow of auxin when growing Cannabis plants, and one of those is to top or pinch out the top growth shoot, by leaving behind the two small auxiliary shoots to grow as a symmetrical pair.

Cannabis topping vs fimming

The way that fimming Cannabis differs to topping is by purposely leaving 30% of the top shoot remaining on the plant, then allowing the plants to focus their energy on the remaining lower foliage.

As strange as the word sounds, the origin of fimming came from the name given to a failed topping / pinching technique. Growers who were unable to get a clean top shoot removal, would end up saying “ Flip...I missed! “ which was then turned into the word fimming and is now part of Cannabis vocabulary across the world.

The Benefits Associated with Fimming Cannabis

• Growers with limited height may find fimming a useful technique for keeping the final plant height short, with a bushy and thick lower canopy.
• This technique causes very little amounts of stress and can be applied once with incredible results, depending on the strain being grown out.
• Fimming Cannabis plants is a great way to promote lower growth and a uniform canopy when using SCROG.
• Growers who endure long vegetative periods with the intention of flowering massive plants can apply this technique multiple times, alongside topping, pruning, tying down, and super-cropping.
• Fimming lower branches also produces excellent results and can eliminate the standard lower popcorn buds forming later into the flower period.

How Does Fimming Cannabis Plants Work?

The way that fimming Cannabis works is by temporarily disrupting auxin, allowing a 5-7 day period where the top shoot that was fimmed, can now recover and grow back with vertical dominance. It is during this time of the vegetative period that the growth structure and appearance will change, causing the Cannabis plants to have a thicker, bushy, and more squat appearance.

By allowing the growth energy that was previously used for vertical growth, the rest of the lower side branches and other shoots will experience a significantly faster rate of growth and development.

Now unlike topping the plants which completely stops apical dominance producing a shorter mature plant, fimming Cannabis allows the plants to begin to grow back to normal after approximately a week's time. The beauty of this easy to perform plant-training technique is, it may be repeated several times until the lights are switched to flowering.

How To Correctly FIM

• Step #1: Start by using a clean and sterile pair of sharp scissors. Make sure the scissors have been wiped with alcohol and are as clean as possible.
• Step #2: Take your Cannabis plant and on the highest point, you will want to gently grip the two leaves together with your finger and thumb.
• Step #3: Take the scissors and perform one clean horizontal snip removing 70% of the top shoot. As long as your scissors are sharp, this should be easy to do leaving a clean cut.
• Step #4: Do not touch the remaining top foliage and simply leave to grow back. You will notice the new growth forming after 7 days and the plants return back to vertical growth.
• Step#5: Repeat if necessary until you are happy with the final appearance of your Cannabis plants. Applying this technique works well, however performing many times over a long 18/6 period will result in very heavy flowering plants.

Mistakes To Avoid when Fimming Cannabis

Fimming Cannabis In Flower:

Only ever perform this plant training technique during 18/6 and when plants have the time to recover and return to normal vertical growth. Fimming Cannabis when plants are producing buds will cause serious amounts of stress and inhibit flower production.

Using Blunt Scissors:

The trick to fimming Cannabis is to use a clean and sharp pair of scissors and to achieve a clean sideways snip. Using blunt scissors will only jeopardize the amount of foliage that is left behind.

Fimming Autoflowering Cannabis Plants:

It is a bad idea to apply fimming to autoflowering cultivars as this will cause plants to become stunted and produce very little flower.