We have talked a lot about how to grow, when to harvest, proper dry and cure techniques and best methods for dry and wet trimming. So, you have planted your garden and are keeping a pretty close an eye on your plants, but you notice something out of the ordinary. What do you do?
Symptoms of Cannabis Deficiencies
Most issues that occur in the garden can be linked to three key components – environment, nutrition and watering. Any variation or inconsistency in these things can have a huge impact on the health of your plants. Cannabis deficiencies can appear on the leaves and the plant in a variety of ways, depending on the issue at hand.
These symptoms can include:
- Brown or dark spots on the leaves
- Leaves that appear to have “blisters” and/or look glossy
- Leaves turning yellow
- Red or pink coloring on the leaves
- Edges of leaves pointing up
- Leaves falling off
- Burnt tips
- White powdery patches
- Wilting plants
The key with cannabis deficiencies, is to catch them early. The sooner you notice an issue in your garden, the more likely you will be able to fix it and recover your plant(s).
Causes of Leaf Issues
Sometimes a cannabis deficiency is caused by stress and may clear up on its own once the stress passes. However, there are certain cases where a deficiency can be a result of improper care or environment. Possible causes can include pH imbalance, over or under-watering of plants and/or nutrient deficiencies.
One of the first things that should be checked if you notice anything odd about your cannabis plants is the pH level. This is one of the most common reasons for leaf issues and/or death as improper pH can affect the roots ability to take in nutrients.
In some cases, deficiencies that may appear to be due to nutritional issues, can actually be caused by incorrect pH, which is blocking the plants ability to absorb what it needs.
While most common in hydroponics, it can also occur in soil gardens. The resulting stress from inconsistent pH can cause brown spots to appear on the leaves.
Overwatering or Underwatering
One of the second biggest causes of leaf discoloration or death is related to water intake. Both overwatering and underwatering can lead to detrimental damage for your garden.
Overwatering essentially results in the roots being drowned and can lead to root rot, which will quickly kill your plant as the roots are no longer functional and able to absorb water or nutrients. This can be caused by both watering too much, as well as watering too often in some cases.
Overwatered cannabis plants are typically droopy with leaves that curl downwards. In addition, the leaves may be yellowing or show other signs of nutrient deficiency.
Underwatering can also have negative effects on your plant as plants need water to survive. Plants that don’t have enough water often have thinner leaves and appear “lifeless”. Chronic under-watering can also lead to yellowing leaves and nutrient deficiencies.
While cannabis plants do require a lot of water, the amount of water held by the soil, the growing stage, size of the plant, and more will dictate exactly what is required by that particular plant.
If you have crossed off pH imbalances or poor watering procedures, the next likely cause of your leaf symptoms would be a nutrient deficiency. There are a variety of possibilities for nutritional deficiencies, many of which have unique symptoms.
Keep in mind, it is normal to see yellow leaves late in the flowering cycle! However, if they are occuring during growth or the early flowering stages, it could be due to one of the following:
- Calcium Deficiency – Appears on newer or growing leaves in the form of dead areas, brown spots, crinkling or curled tips and stunted or distorted new growth.This often occurs in soil that has not been supplemented with calcium or that which is acidic (pH below 6.2). It can also occur when the grower uses filtered or reverse osmosis water to feed the plants or if the plant has too much potassium.
- Copper Deficiency – The leaf symptoms that typically occur involve dark leaves taking on blue or purple undertones. In addition, the tips of the leaves will turn pale yellow or white, which will be quite the contrast to the darkened leaves. This is typically caused by a pH imbalance as most soil contains copper elements.
- Iron Deficiency – Similar to calcium, a lack of iron shows on new leaves. Bright yellow (almost white) coloration on new growth is a signature side-effect of this deficiency. This can sometimes occur if too much chicken manure is used as a fertilization, or the adjustment of pH level. To resolve this issue, more iron is rarely required as it is likely in the soil and pH level caused a lack of uptake.
- Magnesium Deficiency – This appears as light green or yellow coloring on the veins and edges of lower and older leaves. This is because the plant is pulling magnesium from lower leaves to feed new growth, resulting in death of the lower leaves. If you are using reverse osmosis water, be sure to supplement it with magnesium.
- Manganese Deficiency – This results in leaves that are yellow between the veins and may also have mottled brown spots. These patches can spread and eventually lead to leaf and plant death. Most often, this occurs due to a pH imbalance.
- Nitrogen Deficiency – If new growth is not receiving enough nitrogen, the plant will pull it from the lower leaves. Therefore, the older, lower leaves will turn yellow and wilt, eventually dying and falling off..
- Bear in mind, nitrogen toxicity is just as deadly to your plant. This occurs as new growers can often give too much nitrogen accidently, especially during flowering. In this case, the leaves will end up dark, shiny and folded downwards.
- Potassium Deficiency – This can appear on both older and newer leaves and typically starts out looking like a nutrient burn, however, while the edges of the leaf turn brown and appear “burned”, there will also be yellowing in the margins.
- Phosphorus Deficiency – Again, this particular issue typically appears on lower, older leaves. These leaves may turn dark green or yellow. More noticeably they will have brown or bronze spots, sometimes blueish. This can be caused by a pH or root issue, but also colder temperatures. An environment below 60°F (15°C) or one that has recently experienced a large temperature swing, can affect absorption of phosphorus.
- Zinc Deficiency – This causes younger leaves to yellow between the veins. In addition, the plant may stop growing vertically therefore resulting in less space and new leaves to bunch together.
- Sulfur Deficiency – Lastly is a sulfur deficiency, which looks similar to a nitrogen deficiency and causes yellowing of newer leaves. However, underneath the leaves will also take on a pinkish red or orange color. Correcting pH typically resolves this issue.
Keep in mind, nutrient deficiencies can also be caused by stress. If your pH is at an appropriate level, consider whether any dramatic changes have occured within the environment. If not, you can start treating the nutrient deficiency itself.
Another potential cause of leaf issues is “nutrient burn”. In this case, the plant is receiving too many nutrients. When this happens, the overabundance of nutrients can lead to a brown or yellow “burn” on the tip of the leaf. If nutrient levels are not adjusted, the burning can move inwards and result in the leaves becoming crispy or twisted.
While this can also happen to young seedlings, generally it will be corrected as the plant uses up the nutrients. If your plant is a little older, however, it is best to do a flush.
Light & Heat Stress
For outdoor growers, this is not likely an issue that you will encounter. However, indoor growers are required to set up grow lights in order to facilitate cannabis plant growth in their garden. In some cases, these lights can result in stress of your plant.
In order to avoid light and heat stress from grow lights, it is best to ensure your plants are a reasonable distance from the light source. While fluorescent lights generally don’t have enough power to cause light stress, they do typically get quite warm and can result in heat stress. LEDs, on the other hand, are generally more efficient, producing less heat but more powerful light.
Using powerful lights with a broad spectrum results in more potent buds and bigger yields – provided they are kept the right distance from your plants. The “right distance” can be a bit tricky, unfortunately. It often depends on the light source itself, as well as the wattage and your grow area. Also remember that older bulbs will give off less light/heat than newer bulbs. A general rule of thumb for low wattage is 8″ but for more powerful lights (LEDs for example), a distance of 12″-30″ can be necessary.
Fungal or Pest Infection
The last major cause of leaf issues or death is a fungal infection or pest infestation. While outdoor gardens typically experience less issues with pests due to the natural ecosystem (ladybugs and spiders take care of mites, etc), indoor growers have to be vigilant. Unfortunately, if an infestation takes hold, it can be hard to save your garden.
Pests that can affect your cannabis garden include aphids, fungus gnats, thrips, green flies, black flies, mosaic virus, spider mites, caterpillars, inchworms and whiteflies. In some cases, the infestation (typically mites) will not be visible to the naked eye. In this case, you can often tell there is an issue as plants will show signs such as blistering, becoming glossy or twisted and specs on the leaves.
The key is to check your plants daily, and act quickly if pests are spotted. If there are bugs that aren’t supposed to be there, be sure to spray the top of the leaves and also lift them up and spray the undersides; bugs often like to hang out there.
Preventing & Healing Sick Plants
If you have noticed deficiencies or sick plants in your garden, there are some things you can do to help the recovery process and prevent any future deficiencies.
1. Manage and Monitor pH Levels
As you no doubt noticed, poor pH level can affect many areas of the cannabis plant and even result in several of the nutrient deficiencies listed above. Unfortunately, if pH level has been incorrect, brown spots can appear on the leaves. Once these spots occur, they will be unrecoverable. However, balancing the pH level will prevent spotting to spread to other leaves.
Remember – a healthy pH range for cannabis plants is between 6.0-7.0 pH for soil and 6.0-6.5 pH level for hydro grown plants.
2. Provide Good Quality Nutrients
If your pH level and it is fine, but you are still dealing with yellowing leaves, brown spots or another symptom it is likely due to nutrient deficiency. One of the key things to do to resolve a nutrient issue is to flush your plant(s) with clean water containing a regular dose of nutrients; ensure the water is within the proper pH range. This will help to flush out any nutrient imbalances and provide your plant a balanced “refeed” of proper nutrients.
As much as you may want to over-feed your plant with the nutrient you suspect is missing, it is best to do a full sweep instead; you can easily create more issues by introducing too much of a missing nutrient at once. Also ensure that the nutrients you are feeding are of good quality, preferably from organic sources.
3. Monitor Water Levels
A good rule of thumb for watering is to wait until the top of the soil is bone dry – about an inch deep – before watering. The trick is to add water until some of the runoff drains out of the pot. Once this starts, stop watering and give the plant a chance to soak some of it up. If the top of the soil remains wet, you may need to add less water at at time. It is a good time to consider improving the drainage of your pots/soil as well.
Essentially, you should be watering your plant every 2-3 days; if the plant needs longer to dry out, provide less water at a time. If it is drying out quickly, then you can add a little extra.
4. Check Leaves for Recovery
If you have made necessary adjustments to pH or nutrition or watering process, the last step is to monitor for recovery. In most cases the damage is done, but monitoring ensures that no new growth or additional leaves exhibit signs of damage.
The best advice to spotting cannabis deficiencies – and growing quality plants – is to be invested in your garden. Cannabis is a very hard hobby if you only have half an eye on the situation. Being invested in your plants by monitoring growth, inspecting them on a regular basis and having an action plan for potential issues, is the best way to prevent such issue; and clear them up quickly if they occur.