Fimming Cannabis for Bigger Yields: When & How

We’re all trying to get the most out of our plants and fimming is an often overlooked tool in a growers arsenal. When compared to topping, fimming is faster, less risky, and can result in even larger yields. Sadly, there’s no such thing as a perfect system, and it’s not without its flaws but many growers find the results worth the effort.

What is fimming?

At its core, fimming—sometimes written “FIM”—is virtually identical to traditional topping. Fimming is an advanced high-stress training (HST) growing technique that creates extremely bushy plants and is more concerned with developing lateral branches instead of vertical growth. If you’ve ever topped a plant, fimming will be a breeze, however, even novice growers can utilise this fairly straightforward method. It was created by accident after all.

The history of fimming goes back to an American grower sometime in the late 1990s. As the legend goes, an ambitious but careless grower was topping their plants when they realised they had missed their mark and cut at the wrong spot. In their frustration, they shouted “F*ck, I missed” (FIM). Instead of scrapping the project, they decided to let the plant grow and see what happened.

Well, after a few days, the plant had not only recovered but was thriving with the recently trimmed area having developed into a tangle of branches. Each of these turned out to be highly productive, and the grower’s harvest was their best ever.

While the specifics of the story may or may not be 100% accurate, fimming has proven itself to be an incredibly valuable growing technique for controlling a plant’s size and shape.

Fimming vs topping

Before going into greater detail about how to fim your plants, it’s important to understand how fimming is different from normal topping and why a grower would choose one over the other. At the most basic level, fimming and topping are functionally the same; both require you to remove a portion of the top of your plant to create more flowering sites. The difference lies in exactly where you make the cut.

Topping—or “apical pruning” as it’s more technically termed—is perhaps the most well-known HST technique out there. To top a cannabis plant, growers simply remove the freshest growth above a chosen pair of lateral branches. These two branches will then grow into the plant’s main stalks and each produce a cola of their owl effectively doubling the yield of a single plant.

Fimming is incredibly similar with one small twist. While topping requires the complete removal of all vegetative growth above a certain point, fimming leaves behind 20-30% of the trimmed leaves. This might seem like a small difference, but the results are night and day.

As mentioned, topping results in all of a plant’s energy being put into the two newly-created stems. This has several benefits but the plants still tend to grow traditionally; just with two stalks instead of one. Fimming, though, is more concerned with slowing the plant’s vegetative growth for five to seven days.

This forces the plant to divert all of its resources into the undamaged lateral branches and results in a much bushier plant. Overall, fimmed plants will grow slightly taller than those which have been topped owing to the reduced recovery time.

Fimming vs pruning

Pruning is a very broad catch-all term that describes any form of topping, trimming, or defoliating. Fimming is one form of pruning, though so are topping, lollipopping, and (to an extent) mainlining. Since “pruning” is such a general term, it isn’t commonly used with many growers choosing to be a bit more specific with their terminology.

The pros and cons of fimming cannabis plants

Pros of fimming

Just like every other technique that growers have invented over the years, the goal of fimming is to maximise overall yield. However, while something like lollipopping is all about making the most of the fewest sites, fimming aims to maximise the number of flowering sites a plant has. While often considered something of an “advanced” technique, anyone with a pair of scissors and a bit of dedication can pull off a successful fim.

One of the biggest draws for growers is fimming’s versatility. While topping can only be performed on the very top of a plant, fimming can be done to any part of the plant where new growth is present. For example, the lower branches of a plant are known for being less productive than their higher-up counterparts and fimming can help turn these lower areas into production powerhouses.

This makes fimming a popular choice for ScrOG growers as fimming can prevent the classic Christmas tree shape. This allows for a much more even canopy, allowing more flowering sites access to a full dose of sunlight.

When compared to traditional topping, fimming is much less stressful on a plant allowing for faster recovery time and less waiting between harvests. Additionally, fimming doesn’t require quite the same precision as topping and errors are less of an issue. The entire process did come from a mistake, you know.

Lastly, properly fimmed plants are noticeably bushier than topped or untrained plants. This might not be ideal for every grower, but for those with limited headroom but ample area, fimming can help make sure that their plants are making the most of their space.

Cons of fimming

No growing technique is perfect. While fimming has a place in any grower’s toolkit, it isn’t ideal for every situation.

The single biggest drawback of fimming is the potential harm it can do to a plant. Any time you start cutting into a plant and removing growth, you run the risk of causing further harm. This can be greatly reduced by using sharp, clean scissors and by double—and triple—checking what and where you plan to cut before you even start.

When it comes to pruning, there’s always the danger of removing too much. If you’re topping a plant, removing too much growth can cause irreparable harm by removing any potential future growth site. However, with fimming, this particular risk is greatly reduced. Since your goal is to leave behind 20-30% of growth at the target site, removing a little bit more or less than you’d planned on isn’t a huge deal. Even if you go way overboard, all you’ve done is successfully top your plant.

On the flip side, if you don’t remove enough growth during the fimming process, the resulting branches may not grow in thick and sturdy enough to support their buds. While fimming is quite forgiving, there’s a very fine line between too much and not enough. As with anything, practice makes perfect.

Lastly, fimming tends to create very bushy—almost chaotic—plants. You’ll need to practice some pretty extreme low-stress training (LST) to keep things from getting out of hand.

When to start fimming?

Since fimming is fairly high-stress, it’s important to wait until a plant is established and healthy enough to survive the trauma; ideally around the fifth or sixth inner node. This will make sure that your plant has enough support structure to survive but that it’s still young enough to recover before flowering.

Overall, earlier is better than later since one of the main goals of fimming is to help control the size and shape of your plant. The most important thing to remember, though, is that you need to fim your plant well before you start flowering. Generally speaking, HST during flowering is a pretty major no-no as plants will divert precious time and resources away from growing flowers to fix the damage you’ve caused.

DO NOT fim plants less than two weeks before switching to flowering, they need time to recover.

Finally, don’t go overboard. In theory, there’s no limit to how many times you can fim a plant, though you’ll start seeing diminishing returns after a few rounds. While the goal is to create more flowering sites, don’t create more than your plant can support. Larger plants require larger pots and trying to overstep will just lead to a reduced harvest full of tiny popcorn nugs.

What tools are needed for fimming?

If you’ve been growing long enough, then you already have everything you need. The only tools required are a good sharp pair of scissors and some flexible garden ties. Additionally, some wooden support dowels may be a good thing to keep on hand as the fimming can result in thinner branches than some other techniques.

How to fim cannabis plants

OK, now that we know all about the “why” and the “when”, it’s time to go over the “how”. As mentioned above, if you’ve ever topped a plant, then fimming will be an absolute cakewalk. However, if this is your first time, then don’t worry as it really is incredibly simple.

Step 1: Clean your gear

As mentioned, cutting into a plant isn’t without risk. By sterilising your scissors with some rubbing alcohol before you start cutting, you can greatly reduce the risks of introducing foreign pathogens. Even a small infection can run rampant if left unchecked and plants are at their most vulnerable at this stage.

Step 2: Make a gameplan

You’re not Edward Scissorhands flying by the seat of your pants and hoping for the best. Take the time to plan things out. How many branches are you aiming to create? Where will you tie them down? Will they overlap or compete with each other? Sadly, these aren’t the kinds of questions I can answer here as every plant and grow room is unique.

The most common site for fimming is the very top of the plant and that should be your focus; especially if this is your first time. However, anywhere experiencing new growth is a potential target and the tips of lateral branches are also viable choices for fimming.

Step 3: Make the cut

The single most important part of the entire process and you really only get one shot. Grasp the leaves you want to trim firmly between your thumb and forefinger and pull them until they’re taught—DO NOT pull them off the plant. Next, make a single, smooth, horizontal cut removing 70-80% of the leaf. That’s it.

Step 4: Let the plant recover

Give your plant five to seven days to recover. After about a week, you should see that the area where you cut has split into multiple new branches with new growth slowly forming.

Step 5: Repeat

As I said earlier, it is theoretically possible to fim a plant indefinitely. However, most growers find that anything more than two or three rounds delivers diminishing returns.

Step 6: Low-stress training

As soon as your new branches are large enough to be tied down, you should start training them. Fimmed plants (especially those fimmed multiple times) can quickly become untidy messes so make sure that you stick to the gameplan you made in step 2.

Fimming autoflowering plants

Overall, I can’t recommend using any HST techniques on autoflowering plants as they tend to develop too quickly to see any benefits. Since most autoflowering strains begin flowering after only a couple of weeks (this cannot be slowed down or delayed), the window for any fimming or topping is incredibly narrow. In theory, though, it is technically possible to fim an autoflowering strain and if you’re committed to the idea then there are a few things you’ll need to keep in mind.

First off, you’ll need to use a sativa-dominant strain since these typically have longer vegetation periods. Many indicas begin flowering after only three weeks or so, which means that you’ve got a roughly three-day window to fim your plant. Using a sativa will buy you another five to seven days to work with.

Also, when fimming an autoflower, it’s best to err on the side of caution and remove a bit less growth than you might feel is ideal. Going overboard here can completely halt your plant’s growth as it’s getting into the pre-flowering stretch phase. This will severely reduce your harvest.

Make the cut

Whether you’re looking to shake things up, or you’re a newbie experimenting with HST for the first time, fimming is a technique very much worth considering. While it won’t always be the best fit for every situation, the speed and ease of fimming make it a valuable skill for any grower.

Disclaimer:
Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.

Fimming Cannabis Plants for Bigger Yields: When & How