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Cannabis Leaves: Everything You Need to Know

Understanding the Inner Workings of Cannabis Leaves

The Cannabis leaf is a highly recognizable symbol of 420 culture and is a very prominent part of the cannabis plant itself. Sure, the leaves can contain some small roles in growth and development. Understanding leaves, what they do, and how they work can help you keep your cannabis crop healthy, so you’ll enjoy a bigger, more bountiful harvest.

In this overview we will discuss the anatomy of the cannabis leaf as well as how to diagnose and treat some common problems encountered by home growers. Although there are many varieties of cannabis, there is very little alteration on how the leaves look like from one strain of cannabis to another. Here are some of the other facts you should know about cannabis leaves.

Taking a Closer Look at Cannabis Leaves

Marijuana leaves certainly vary widely in shape, size, color, placement, and other aspects depending on the specific strain you’re looking at. Mixing different strains creates entirely new leaf appearances that have combined traits of the types of cannabis used in the hybridization process.

Upwards of 800 strains are now recognized by the cannabis community and more are continually being developed. Because of that, the leaves on your plants may exhibit any number of visual characteristics. That being said, certain components are universal regardless of the strain you’re growing.

Those elements allow the leaves to perform their many duties. They also work in tandem with other parts of the plant to carry it through its lifecycle from the seedling stage to harvest. All leaves have a few basic mechanisms that are clearly visible on the surface.

  • Petiole: Petioles are the parts that attach the leaves to the larger stems of the plant. Throughout the life of the plant, they help maintain balance and nutrition in the leaves.
  • Midrib: Petioles give way to the midrib at the base of each leaf. These are the main veins running through the centers of leaves.
  • Veins: Veins are parts of the circulatory systems of plants much like our own blood vessels. They branch off from the midrib in various patterns. Those patterns are generally different in each cannabis strain.
  • Lamina: The lamina is the flat part of the leaf. It gives the leaf its shape and structure while providing support for the midrib and veins.
  • Margin: Margins are basically the edges of leaves. They’re often used to when identifying plants based on their leaf shapes. Some are smooth whereas others are curved or serrated.
  • Tip: As the name indicates, the tip is the end of the leaf opposite the base. It’s also the area where the petiole transitions to the midrib. It’s where the midrib ends, and the margins meet.

Those are the primary outer parts of leaves. Of course, they’re only the ones you can see from the outside. Leaves are also made up of countless individual cells. Different types of leaf cells perform specific functions.

Digging Beneath the Surface

Despite being extremely thin, leaves consist of different layers. Each layer is made up of specific types of cells. Some of those can be found throughout the plant whereas others are unique to the leaves. Both general and specialized cells make up cannabis leaves, and they occur in different layers.

  • Epidermal Cells: Leaves’ outer layers are known as the epidermis. Epidermal cells cover the lamina of leaves and protect them against the elements. On the top sides of leaves, epidermal cells are thin and translucent to allow sunlight to reach the layers underneath. Cells on the undersides of leaves aren’t translucent, but they can swell or shrink to create different levels of airflow.
  • Guard Cells: These are the cells that tell the epidermal cells on the undersides of leaves when to open or close for oxygen and carbon dioxide exchange. They monitor the conditions outside and inside the leaves to determine when more or less airflow is needed.
  • Palisade Mesophyll: These types of cells lie underneath the epidermal cells. They’re the ones that contain the chlorophyll that gives plants their color. Sunlight filters through the epidermis of the tops of leaves to the palisade mesophyll below where it’s absorbed.
  • Spongy Mesophyll: Below the palisade mesophyll, you’ll find spongy mesophyll. These cells are less tightly packed than those in the layers surrounding them. They transport moisture and nutrients to the palisade mesophyll. They also carry substances to other parts of the plant.
  • Vascular Bundles: These cells are found in leaves, but they also exist in every other part of a cannabis plant. They make up plants’ circulatory systems. Vascular bundles carry substances throughout the plant.

All these layers and the cells they’re made of come together to form an intricate system. They make possible all the processes plants like Black Hulk and Auto Banana Kush need to go through to grow and thrive. We’ll discuss those processes in further detail shortly.

Classification of Cannabis leaves: phyllotaxy

In terms of leaf arrangement, cannabis leaves are not ‘alternate’ as most of the other herbs in the same family, but rather, they are compound and decussate-opposite. The leaves emerge in pairs on either sides of the stem and they also have a characteristic vertical line in between the spaces. Though the leaves are decussate when they are young, they normally begin to form alternate patterns as the plant nears flowering stage.

Leaf difference between the three main strains

The three main cannabis strains are sativa, indica and ruderalis. From a broader perspective, the leaves may be seen to have no difference amongst them, but a close look will reveal subtle differences as follows:

Sativa leaves – the leaves are long and slender. They have very conspicuous serrations which make them look spiky and jagged. The color of the leaves is also distinct and normally ranges from blackish green at the darkest to lime green. A fully grown sativa leaf can contain up to 13 leaflets.

Indica leaves – these leaves are wider and larger compared to their sativa counterparts. A fully grown indica leaf may contain between seven and nine leaflets and the color is normally deep olive green. It is not common for you to find this strain with very light green leaves and if that happens, then it points to a deficiency.

Ruderalis leaves – these are the smallest among the strains and a fully grown leaf may have anywhere between five and thirteen leaflets. In terms of width, the almost equal indica, though at times they can be narrower than any indica leaf can be

Leaves and Their Roles in the Cannabis Growth Cycle

With the basic parts of leaves covered, it’s time to move on to what those components do and how they factor into the marijuana lifecycle. You’re probably aware that plants need light and heat to grow. If you’ve planted your cannabis outdoors, it’ll get its light and heat from the sun. For those of you who are growing indoors, the plants will get those elements from grow lights.

Photosynthesis Explained

Either way, light filters through the thin, transparent epidermis of the top sides of leaves and is absorbed by the chlorophyll-equipped palisade mesophyll layer beneath. At the same time, the plants’ roots draw in moisture and nutrients from the soil or growing medium surrounding them. Water, vitamins, and minerals flow upward through the plants’ circulatory systems and the spongy mesophyll until they reach the cells in the palisade mesophyll.

In the meantime, the cells inside the thicker epidermal layer on the bottom sides of the leaves expand and contract to allow carbon dioxide from the air around them to enter the leaves. When all those elements come together in the palisade mesophyll, those cells combine them to create food for the plant. Then, the spongy mesophyll takes the food and distributes it throughout the plant as needed. All those steps are part of the photosynthesis process whether you are talking about indoor weed plants or outdoor weed plants.

Exploring Plant Respiration and Transpiration

Photosynthesis is only one process plants need to carry out to survive. The much-needed flow of moisture, vitamins, minerals, and other elements throughout the plants is known as transpiration. Plants also need to breathe. This happens through respiration. We’ve already touched upon how leaves draw in carbon dioxide, which is part of the process, but we’ll go into further detail now.

As those cells on the undersides of leaves inhale carbon dioxide, other cells absorb it and mix it with moisture and nutrients for food production. All this generates glucose, a type of sugar, for the cannabis plant to feed on.

Plants generally take in more moisture and create more energy than they need because they instinctually know that it’s better to be safe than sorry. At the same time, like all living things, their biological processes create waste. All the waste and excess need to go somewhere. Otherwise, they’ll build up inside the cannabis plant and detract from its health, potency, and yield.

Respiration comes into play here as well. Those cells on the undersides of the leaves once again contract so the extra moisture and other compounds can be released into the air. One of the byproducts of their food production and consumption happens to be the oxygen we so desperately need for our own respiration processes.

Putting the Details into Action

All those details speak to the importance of leaves and how they work to transform your sprouts into a full-size crop of juicy buds ready to be harvested. They can also give you a great deal of insight into how to take care of your cannabis as it grows.

Feeding and Watering Your Cannabis Plants

Though leaves use water to make glucose, they can’t actually draw in moisture from the outside. That’s the roots’ job. Because of this, be sure to water the roots of your American Haze or Blue Widow plants rather than the leaves. The same holds true for nutrients. If you give your plants extra nutrients, add those to the soil or hydroponic solution so the roots can take it to the leaves from there.

Carbon Dioxide and Ventilation

As mentioned, leaves need carbon dioxide for food production. They glean it from the air around them. If you’re growing a sizable crop inside, you may need to take extra measures to ensure the plants have enough CO2 but not too much.

Ideally, the carbon dioxide levels in the room should range from 800 to 1,500 parts per million. If the concentration in your grow room is too low, you may need to use a system of CO2 cylinders with an automated meter and controller to bring it up to speed. Should the levels get too high, you’ll need better ventilation.

Light and Heat

Also, keep in mind that the lighting in the grow room is crucial. Though leaves’ epidermal layers help protect them from excess heat and light, they’re not invincible. Having the grow lights too close to the plants could burn them but placing them too far away would deprive them of the heat and light to they need to flourish.

Listen to the Leaves

Leaves can also clue you in when there’s a problem. They’re the most visible parts of the plant because they largely cover the stems, and the roots are generally hidden by soil or a growing medium. That means the leaves can tell you a great deal about the health of the plant.

When the leaves begin to droop, they’re probably not getting enough light or water. If the cannabis plant has an abundance of leaves but doesn’t seem to have many flowers, you may be using too much fertilizer. Yellowing leaves are a sign of too much water, inadequate drainage, or too little heat.

Should the leaves start turning brown and brittle around the edges, it’s a sign they’re getting too much heat and light. Be sure to look out for white spots on your leaves as well. This is mold, and it can destroy your plants before they even have a chance to flower and produce buds.

Mutated leaf patterns cannabis

Due to the incredible variation in cannabis morphology in different places around the world, different rather unusual leaf patterns have been noticed. Most of these variations are desirable by most people, especially the illegal growers, since they will not attract a lot of attention from the law enforcers. Some of the variations include:

Webbed cannabis leaves – this is a common mutation and quite a number of breeders have tried to stabilize it. Though their efforts haven’t brought forth good fruits, webbed varieties can now be found in the markets, albeit very few of them.

Whorled leaves – this is another mutation in the cannabis leaves, though it is a less desirable one it nearly looks like the common cannabis leaves.

Australian bastard cannabis – this is the most unique mutation and it was first recognized by breeders around Sydney, who went ahead to attempt to stabilize it, but with no commercial success. With this mutation, the leaves are succulent, with no hairs and each leaf will have utmost five leaflets.


All Things Said and Done

From the moment the first tender leaf unfurls on a tiny seedling, it goes to work to make food, expel waste, and help the plant to thrive. Over time, more leaves develop. In turn, they give the plant what it needs to get taller and bushier during the vegetative state. When the flowering phase takes over, the leaves alter their approach to help the flowers develop into buds.

Leaves are vital to all plant processes. They also do their part to tell you when something is wrong with a marijuana plant or the conditions it’s being grown in. Give your cannabis plants all the elements they need to thrive and keep an eye out for signs of trouble. In the end, you’ll have a healthy crop that’s sure to serve you well