This blog zooms in on cannabis leaves and their uses for plants and growers. As a cannabis community, we tend to focus on the flower buds of our beloved plants, but this blog explains why leaves are crucial for any attempt to grow, understand, and truly enjoy cannabis.
History Of Cannabis Leaves
Cannabis leaves are the most iconic symbol of modern stoner culture. They may well be the most famous and identifiable type of foliage in the world (sorry Canadian flag!). That’s actually weird, since cannabis growers are usually out to harvest the plant’s flower buds, not the leaves. Still, the tell-tale shape of a weed leaf has been making its mark on society for ages. It has been spotted in ancient East Asian cave drawings and Egyptian hieroglyphics, predating the invention of agriculture and crop cultivation in some cases. Moreover, riding today’s wave of legalization and international recognition, cannabis leaves are more ubiquitous in subcultures and mainstream branding than ever before.
So even if most of the medicinal and recreational benefits of cannabis are located in the cola buds of female specimens, it pays off to understand the functions and biology of its leaves. As this blog explains, leaves are crucial for the growth and survival of cannabis plants. In addition, they have been used by shamans, priests, and healers throughout the centuries. However, for growers, they serve another crucial function, signalling many health issues and other problems that plants face throughout their life cycle.
Vital Functions Of Cannabis Leaves
Most plants have leaves, hinting both at their ancient evolutionary origins and their extreme importance in plant survival and physiology. At any rate, leaves make up most of the mass and surface of a cannabis plant, making basic leaf knowledge essential reading for all growers and connoisseurs.
The main biological function of cannabis leaves is photosynthesis. As this blog explains, photosynthesis is a series of chemical reactions allowing leaves to turn (sun)light into energy, which they can store and use to fuel growth and flowering. Leaves are the solar cells of plants, which explains why total leaf surface is such a vital aspect of a plant’s physiology and chances of survival
Nutrient & Water Storage
Cannabis leaves can also be used as a storage facility for water and important nutrients, especially nitrogen. If times get tough, these reserves can be drawn from the leaves and used as an emergency supply. This largely explains why so many cannabis (nutrient) problems become apparent in the looks of the leaves, which can turn yellow or brown due to nutrient shortages.
Breathing & Feeding
Not everyone knows that leaves can also absorb and release various compounds, similar to the main function of a plant’s roots. In fact, this is why plants are so essential to keeping our atmosphere in good shape. When they catch the light, cannabis plants absorb CO2 through the pores or stomata located underneath their leaves. CO2 is used for photosynthesis, to produce the sugars (carbohydrates) that fuel the plant’s metabolism.
In the dark, they release O2 back into the air. This explains why plant life acts as a carbon sink trapping harmful excess CO2 from the atmosphere, and how they can help keep the air in a room healthy. It’s also nice to know that growing weed is a small contribution to keeping climate change in check; or at least to partially offset energy consumption of grow lights for indoor growers…
The pores on the surface of cannabis leaves can also absorb water. This is why growers can water and feed their plants using the leaves in addition to the roots. Spraying water with some nutrients in it can contribute to healthy plant growth, provided it is done in moderation.
Leaves have transport channels through which water drawn up by the roots reaches the leaf cells. This makes leaves firm through a process called osmosis. If the leaves on a cannabis plant start to go limp, the likely cause is water shortage, causing osmotic pressure to drop and cells to go limp, resulting in drooping leaves.
People often overlook the importance of shading provided by the leaves of a plant. Sure enough, they catch light for energy production, but they also keep the lower parts of the plant cool by the shade these ‘solar panels’ cast. This is a bit of a double-edged sword for cannabis growers, however, as too much foliage can restrict the amount of available light for the plant as a whole. Some grow techniques such as SCROG attempt to maximize leaf spread to make the most out of available (sun)light. We have a special blog on pruning cannabis plants that tells you all about what to cut, and what to leave on the stems.
Types Of Cannabis Leaves
We can distinguish between three types of leaves on a cannabis plant: cotyledons, fan leaves, and sugar leaves.
The first things to emerge from a cannabis seed after germination are a tap root and a pair of cotyledon leaves. These baby leaves don’t have the typical weed leaf shape. They are the first miniature solar panels the seedling employs to power development of the true fan leaves that come after.
Fan leaves are the world famous symbol of weed. You could call them the ‘true’ cannabis leaves. Their characteristic serrated edges and slender leaflet fingers are quite easy to spot, which explains their branding value. But not all fan leaves are created equal. Different types of cannabis have different leaf characteristics.
Cannabis indica strains and indica-heavy hybrids tend to have shorter, broader leaves with bright or lime green colours. The differences between indica and sativa weed are disputed, but there is a tendency to discern ‘broadleaf variants’ that are generally indica-leaning in their genetics. Indica broadleaf fan leaves tend to have fewer fingers or leaflets; usually between five and seven in mature leaves.
Cannabis sativa strains and their hybrids usually display longer, slender leaves that have darker hues. They also have more leaflets per fan leaf than indica-heavy strains, often somewhere between seven and eleven or even thirteen in total.
Cannabis ruderalis – the type mainly used in autoflower crossbreeds – tend to have the fewest leaflets, often growing in three-fingered constellation. It is rare, however, to see a 100% ruderalis plant, so these properties usually don’t show in commercial autoflower strains.
Some breeders aim for a specific type of uncommon and mutated leaf shape called ‘duckfoot’. Duckfoot leaves are also three-fingered, but they don’t need to have ruderalis descent. This is a bit of an acquired taste, sought after by specialist growers, but duckfoot cannabis leaves nonetheless deserve mentioning in a blog like this.
The third main type of cannabis foliage is sugar leaves. These are smaller leaves with fan-like shapes found in and around the buds as they mature. Sugar leaves are often loaded with trichomes containing valuable cannabinoids. When harvesting weed, sugar leaf trim should not be discarded, as they can be used for making hash, edibles, and more as this blog explains.
How To Diagnose Cannabis Health Through Leaves
Leaves are an important part of the anatomy and physiology of cannabis plants. For growers, they have another vital function: leaves can be key indicators of a cannabis plant’s health. The various signals and symptoms cannabis leaves can convey are too much to address in this blog, so these will be dealt with separately. However, to give you an indication, cannabis leaves can be used to detect a range of problems including:
- Nutrient Burn/ Shortage;
- Water Issues;
Let’s get one common misunderstanding out the way right here and now. Yellow leaves are often a sign that something is wrong with a cannabis plant. However, there is one case in which yellow foliage is perfectly normal: late flowering. Once the flowering stage is almost complete, the plant starts to shed its fan leaves, which starts by the leaves turning yellow. This is perfectly normal plant behaviour intended to drain leaves of all remaining nutrients for maximum flower bud growth.
Pruning And Leaf Based Training
As mentioned, pruning cannabis leaves can be difficult to master. Our pruning blog gives a few good guidelines, but most growers stick to their personal preferences and best practices when it comes to removing leaves.
Several specialized grow techniques aimed at maximizing harvest yields rely upon removing leaves or altering a plant’s shape to give leaves more room. These techniques, including SCRoG (Screen Of Green), Low Stress Training, and SoG (Sea Of Green) are covered in separate Grow Blogs.
What To Do With Cannabis Leaves?
Once the leaves of a cannabis plant have served their purpose fuelling growth and bud formation, growers harvest the flowers and generally discard the remaining foliage. This is actually a crying shame. Both the fan leaves and sugar leaves have their uses for holistic cannabis enthusiasts; moreover, reusing all that plant material gives your grow that extra touch of sustainability.
Sugar leaves tend to be sticky with glistening trichomes once cannabis finishes flowering. The leaves themselves are too acrid-tasting to smoke, but they are great material for making hash, extracts, cannabutter, or other edibles. Never throw these away while trimming buds – they’re a real treat reserved only for those who grow their own!
Fan leaves don’t contain enough cannabinoids for making hash or other delights. Still, they are full of valuable compounds that any grower can reuse for free. Cannabis leaves make the best compost for next year’s grow. All it needs is a place to decay, without any further effort on the grower’s behalf!
Some growers also make ointments and tinctures out of cannabis leaves after harvest for the non-cannabinoid compounds they contain. Recipes abound online if you’re interested.
Turning A New Leaf
Now that you have some basic knowledge on cannabis foliage, you’re likely to appreciate your plant’s hard work even more than you already did. Knowing what to do (or not to do) with leaves will only improve future grow results. Feel free to browse our Grow Blogs for more cannabis info and tips, or proceed straight to our strains collection and order fresh seeds to turn a new leaf for your next grow…