Whether you've grown other plants or cannabis plants before, or this is your first time, there is always something new to learn that can help you improve your gardening knowledge. With this information, you will quickly become a more confident and successful grower.
The first two techniques we want to talk about are topping and fimming.
To better understand the usefulness of these techniques, let's take a look at why they matter and how plants use their energy and what role hormones play. Plants can be successfully grown in a variety of fashions, adapting to the environment around them, but that adaptation is just to ensure the survival of the plant.
Have you ever seen a plant grow too tall, without a thick stem? When this happens, the plant is considered “leggy” or “etiolated” because it has long legs, but not a strong body. This is what happens when a plant doesn't get enough light, so instead of growing thick from the bottom up, perfect for supporting a heavy canopy, it puts all its energy into growing taller so it can presumably reach more of the light.
This is just one example of adaptation. But there are many more. Such a “leggy” adaptation is one that helps the plant survive, but not necessarily a healthy plant.
So, what does this have to do with your cannabis plants?
Ideally you want a plant that grows flat and broad. A low, broad plant will capitalize upon every photon of light available, and in the end you will get more branches, more colas, and more cannabis.
However, cannabis plants will typically grow tall and skinny, which means that without the right training, they won't grow laterally. Instead, you'll get one main stem with a single cola. When cannabis is flowering, the branches at the top of the plant start producing flowers and these are referred to as colas. Cannabis plants will naturally grow in the shape of a Christmas tree, very tall and skinny.
This display is called “apical dominance”. It determines the directional growth of your cannabis plant. There are different types of apical dominance which lead to different production patterns both horizontally and vertically.
Topping vs. Fimming Marijuana Plants
Topping marijuana plants is a technique where you cut the central apex of the plant off to help encourage lateral growth.
Topping works on any number of plants, not just cannabis plants, but when employed, it works the same way and achieves the same goal: topping off the plant to force lateral growth and prevent auxin production.
When topped, your cannabis plants will force energy into the multiple nodes (or branches) it has early on. This will force them to grow thicker and stronger. You want this because otherwise they grow too tall and too thin.
Fimming is a technique similar to topping, one that requires a cut near the top of the plant, on the central stem or apex. It is used as a slightly less traumatic technique on plants.
Think of it as trimming your hair rather than shaving your head. With fimming, you can encourage bushy growth in your plant and increase your cola yields. Fimming is considered more of a training technique. It forces more lateral branch development, or outward growth, and more flowers.
The funny thing is, this wasn't an official technique used by professional growers for a long time. It was actually an accident that stemmed (no pun intended) from a grower applying the topping technique incorrectly and giving a quick trim rather than a full snip.
The result was a bushy plant with better yields. So all in all, Bob Ross was right when he said we don't make mistakes, only happy accidents.
The official term was FIM, an acronym that stood for “F**k I missed”, referring to the revelatory accident in question. So today we just call it “fim” or “fimming”.
Both of these techniques cause the chemical balance of the plant to change. When we break or remove parts of the plant, it is considered a high-stress training technique, or HST. If you employ an HST, you should give your plant an extra week in its grow schedule to recover. If you’re not interested in high stress training (HST), click here to check out some ways to introduce low stress training (LST) into your grow.
Topping Cannabis Plants
Topping cannabis is when you cut off the apex, or the literal top of the plant. The top of the cannabis plants contain a hormone that controls the apical dominance. Auxins are one key hormone produced through apical growth and transported downward. As the auxins move downward through the plant, they inhibit the growth of lateral tips.
However, they don't travel very far within the plant, so as the plant gets taller, the lower branches are not as affected by the auxins so they can start developing flat and broad. As the cannabis plant gets bigger, the lower branches start to grow wider and broader, but the growth of the top branches is still inhibited by the release of auxins, hence the Christmas tree shape.
By cutting off the apex, you remove the production source for the auxins and in so doing, you stop the auxins from travelling downward throughout the plant and preventing that lateral growth. Breaking the apical dominance can allow your lateral branches to develop so that you can better train your plant using techniques like manifolding and mainlining.
How to Top/ Fim
- Clean your pruning shears. This prevents any transfer of disease like fungus or bacteria to your plant. Remember: when you make a cut on your plant, you are doing just that—making a cut. Consider that if you get cut, your wound is at risk for infection if you aren't careful. The same is true of your cannabis. Use a mixture of 9 parts water to 1 part bleach, or rubbing alcohol to clean the tools.
- Find the area you are going to remove. It is best to remove closest to the top, so looking at the image below chopping at node #6 is what we recommend.
- Cut the entire node if you are topping, or just the tip of the leaves if you are wanting to fim.
- Discard the removed plant matter.
- Add a week to your grow schedule to allow the plant to bounce back from the stress of this technique.
If you look down at your plant directly, you will see the top central branch, or apex, which is to be cut. The image below shows what the top looks like before you cut, and the new main branches that are revealed after.
Pro Tip: You should never top a plant that is struggling. If your plants struggle early, and you top it, it can cause irreversible stress to the plant.
When is Best to Top Cannabis Plants
This is a technique you want to use when your plant is in its third or fourth week of vegetative growth, when it has 4-6 nodes or sets of branches.
Some growers go as early as 3-5 nodes or sets of branches while others advocate waiting until 5-6 nodes have developed. Waiting until 5-6 nodes will allow the cannabis plant to recover faster since it has a bigger photosynthesis area as it has more leaves.
Never top your plant when it is flowering because this phase alters how the plant grows. Things like nutrient requirements and the way energy is focused change, and if you top the plant now, you can reduce yield. How? Because it will force the plant to use its energy to repair the cuts rather than develop the buds.
If you've done it successfully, the plant will grow larger lateral branches, instead of just one large central branch.
With some strains, where you would otherwise get 25 grams in a large main cola, you might use topping and instead get only 10 grams in each cola. You do run the risk of reducing your yield a bit with topping, depending on the strain.
This is determined by the genetics of the strain you are using. So, do some extra research or basic trial and error to see how your specific strain responds.
Fimming Cannabis Plants
We do fimming for the same reason as topping: to stop the production of auxins and control the apical dominance. Your overall goal is to get more lateral branch growth on your cannabis so you don't end up with the Christmas tree shape and a single cola.
By cutting off the very tip of the central top branch, which is known as the centre or the centre apex, you are forcing your plant to not only put more energy into the nodes that are growing outward rather than the central branch growing upward, but you are limiting the hormone production that would impede this outward development at the same time.
When to Fim
Now, with fimming, you don't have as many concerns as with topping. The strain matters less here because you are not drastically removing an entire node, but rather, trimming the leaves to achieve the same energy disbursement on the lateral branches.
Timing is still important. When you are fimming your cannabis, you never want to do it after the plant has flowered. Much like topping, you can encourage the plant to force more energy into its outward growth if you fim it before the flowering stage.
If you've fimmed your plant successfully, the plant will grow larger lateral branches, instead of just one large central branch, which will help develop a wider canopy and, in the end, provide you with better buds.
Does It Only Work on Cannabis?
No, these techniques are applicable to a wide range of plants, and they bring about the same results.
If you have a big garden with more than just cannabis growing, you can use topping for your tomatoes, all varieties of peppers, even flowering herbs like basil or oregano. If you plan to use these techniques on other items in your garden, be sure to do them before the plants start flowering, otherwise you will ruin the yield you get of whatever you are growing, be it flowers that produce peppers or tomatoes, or just bushier basil leaves.
Which Technique is Better?
Realistically, most growers don't intentionally use fimming. Most people like topping because it is a slightly more reliable technique for producing bigger, healthier plants.
So, if you must choose, go with topping. You will find that topping encourages thick, bushy plants that most people aim for, rather than the thin, straggly plant that slumps over from its own weight.
Remember that these techniques both can reduce the height overall, but in most cases, will give you more buds.