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Can You Read a Weed Leaf?

If you want to be good at cultivating cannabis and maintain a healthy crop, it makes sense to do your homework on how to maintain a healthy plant.

Understanding the lifecycle of your plant is part of that and easy to pick up from articles online but so is learning to spot problems that may occur. The truth is that the humble weed leaf can tell you quite a lot about what’s going on with your plant.

That includes whether there are problems with what you are feeding your crop as well as problems such as pests and fungi. Here’s our quick guide on the wonders of the weed leaf.

Biology of the Weed Leaf

Leaves are the powerhouse of any plant, providing all the energy. Flowers and buds are means of propagation. Without leaves providing power, a plant will quickly die. You can remove the buds and any plant will easily survive. It’s the same with a cannabis plant as it is with any other plant.

Your weed leaf is essentially a hi-tech solar panel. The green pigment, containing chlorophyll, is integral to this. It helps perform photosynthesis which uses sunlight to help make nutrients from carbon dioxide and water. Water comes up through the roots and the CO2 is drawn in via tiny holes or stomata on the underside of the leaf.

The leaves can also absorb other nutrients through those stomata which is where the process of foliar feeding (spraying fertilizer directly onto the plant) comes in.

The reason that leaves are so good for the environment and us as human beings is that a by-product of photosynthesis is oxygen which is released into the air. Take away all the green plants in the world and we’d have nothing to breath.

Types of Weed Leaf

There are three main types of weed leaf and most cannabis enthusiasts will probably recognize them immediately. When strains are developed, many use a mix of these three different types and that can change the way the leaves look but they still retain the main characteristics.

Sativa Leaves

Sativa strains tend to create tall plants that have longer flowering cycles. They grow better in warmer climates and the cannabis is characterized as invigorating and enlivening which makes it great for use at social occasions.

The sativa consists of fairly narrow, long finger-like leaves. There can be as many as 12 or thirteen of these that comprise one main leaf. Each has a lower amount of chlorophyll than other varieties of cannabis and that could potentially contribute to their slower flowering time.

Indica Leaves

Indica plants are generally a lot smaller in height than sativa varieties. With short flowering cycles they are better suited to cooler climates but can actually grow anywhere. Indica varieties have a sedating effect which makes them better for chilling out and relaxing.

The weed leaf, like the plant, is short and quite wide. Unlike sativa, there are probably only going to be seven or less fingers and they are a darker shade of green. That’s because of higher chlorophyll levels which also mean you get a faster flowering time.

Ruderalis Leaves

Probably less well-known, the ruderalis has thin fingers like the sativa but fewer of them. In fact, they can often get mistaken for immature sativa plants. It’s common to find these in areas like eastern Europe and Russia.

The plant has low levels of THC and so won’t get you high. It was first used to create fast autoflower plants and that remains the primary interest for this variation of the cannabis plant.

What Are Mutations?

Every living thing can mutate when it procreates and breeds. That’s basically down to genetics. This happens by chance but is also initiated by growers who are trying to develop new strains. This can give rise to slightly different looking leaves with a little variation in what the final crops look like. It’s not a major factor but something you should be aware of when you start to grow your next harvest.

In other words, just because your leaves don’t look exactly like they do in the pictures doesn’t actually mean there is something wrong with them.

Spotting Problems With Your Weed Leaf

Now that you know what each individual leaf looks like when it’s healthy, it’s time to consider what to keep an eye open for when you are cultivating your crop. You don’t need to have a major in plant biology to notice that something is wrong.

A problem with the leaves can mean that your crop is suffering so a little awareness, however rudimentary, can help you put things right and still get a good harvest.

Common Weed Leaf Pests

As with all plants, there are certain pests that like to feed on them. You are more likely to encounter these if you grow outside but they can be a problem indoors too. The first of these is the leaf miner which is pretty aptly named. While they are very small, they do leave tell-tale small holes in your leaves which are quite easy to spot. When mature leaf miners change into flies but the damage to your plant is done by the larvae. You may also notice white streaks in the weed leaf veins. There’s one natural way to get rid of these and that’s using neem oil which can be rubbed onto the leaves. The other major pest you might come across is Leaf Septoria which is a fungus that creates yellow spots. Inexperienced growers can mistake this for lack in nutrients. It tends to appear at flowering times and quickly begins to spread. A fungicidal spray should solve the problem but increasing ventilation around the plant can actually stop the problem from occurring in the first place.

Yellowed Leaves

As just mentioned, yellowing leaves can be a sign that you have your plant feeding wrong. This is quite a common issue with cannabis, especially when you are growing it indoors. The trouble is that this is not always that easy to diagnose.

It could be down to too much fertilizer in the soil. It could mean that the surrounding lights are causing heat damage. Even the wrong pH for your soil can cause a problem because it prevents the uptake of nutrients.

Experience usually tells you what is the exact cause and you’ll pick that up over time. In the meantime, you might want to develop a list of things to check. Here a few specific nutrient deficiencies that you can easily look out for:

  • Nitrogen: this can cause stunted growth, red stems and pale leaves.
  • Phosphorous: similar to nitrogen but the leaves will be partly green and partly pale.
  • Potassium: if you notice the ends of the leaves beginning to brown and curl up, you’re lacking this nutrient.
  • Calcium: small spots of yellow appear on the leaves (this can be remedied by foliar feeding).
  • Sulphur: the leaves start to yellow faintly.
  • Magnesium: the yellowing usually starts in the middle of the plant and begins to spread to the younger leaves.
  • Iron: the yellowing is distinctive with dark green veins showing up against a pale background.

Yellowing leaves generally means you have a problem with too much or too little of any or all of these nutrients. It can also be aisgn that your lighting is too close so try moving your lamps first.

What To Do With Your Leaves After Harvest

New growers generally get a little confused about what value the leaves have on their cannabis plants. Most do except for the large, older fan leaves which have very little cannabinoid content. You can put these on your compost heap and use them to feed your next crop.

The smaller, sugary leaves do have a decent level of cannabinoid that you’ll want to harvest. These leaves are often used to make homemade concentrates but they can also be ideal for combining with food, for example, by turning them into cannabutter.

If you haven’t got time to do anything with these leaves straight away or simply can’t make up your mind what to do, don’t worry. We suggest putting your trim leaves in a brown paper bag and leaving them to dry out. This should take a few weeks. If you’re still not decided put them in an airtight container and pop them in the freezer to maintain their cannabinoid content.

Tips For Keeping Your Weed Leaf Healthy

  • Research your seed strain and find out what is best practice – there’s a lot of information online to make yourself more knowledgeable.
  • Avoid excessive overwatering and make sure that the soil you use has very good drainage, whether you are growing indoors or outdoors.
  • Keep the pH of your soil in the mid-range (6) if you want to keep your weed leaf growth healthy.
  • Don’t put lights too close to your plants as this can damage the leaves.
  • Go easy on the nutrients and don’t overfeed, especially if you have autoflower varieties.

You should generally check your plants once a day and don’t forget to gently turn leaves over and check their underside too. If you spot an issue, do something about it straight away as delay might cause you more problems.

Check out our beginner’s collection of seeds.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Steven Meredith

Steven is a full-time freelance writer based in Wales. He joined the Seedsman team in 2018, contributing articles on a number of topics including global news, cultivation and strain profiles.