Cannabis Nutrient Deficiencies in Sick Plants
November 14, 2018

Cannabis Nutrient Deficiencies in Sick Plants

The most common deficiencies and how to reverse them
MarijuanaBreak Staff / Updated on November 14, 2018

Cannabis Nutrient Deficiencies in Sick Plants

If you’re a novice grower, you’ve probably spent countless hours scouring the internet hoping to uncover the secret to growing fat, juicy, potent buds. Admit it, when you found out what it takes, you were a little disappointed, right? There is no ‘magical’ growing method. Instead, you need to ensure your plants grow in the right climate and provide them with the optimal amount of light, water, and nutrients.

When it comes to growing weed, boring is beautiful! If you have any sense at all, you’ll WANT a dull few months where your plants grow big and strong without any drama. When it comes to nutrients, a lot of new growers tend to overfeed their plants, especially with Nitrogen, Phosphorus, and Potassium.

However, it is possible to focus so much on providing enough of the core nutrients that the lesser known varieties are forgotten about. If your marijuana plants don’t receive the right amount of nutrients, they get stressed and more likely to suffer from a pest infestation, a disease, or exposure to other pathogens. The result is stunted growth and lower yields.

As a consequence, it is essential for cannabis growers to learn how to spot signs of nutrient deficiency. First, we look at secondary micronutrient deficiency followed by the symptoms associated with a lack of the main ones.

Getting the Right pH for Cannabis Plants

The pH scale measures the acidity or alkalinity of a substance. The scale ranges from 0 (most acidic) to 14 (most alkaline) with pure water classified as ‘neutral’ with a pH of 7.0. Every full point on the pH scale is ten times more acidic or alkaline than the previous number. For example, a substance with a pH of 5.0 is ten times more acidic than a substance that’s 6.0.

When growing cannabis, it is important to ensure the water and growing medium you’re using are at the right level. If you grow in soil, make sure the pH is between 5.8 and 6.8 (6.3 is ideal). Reduce it to a range of 5.5 to 6.5 when using a hydroponic system. The pH of the soil and water dictate how well your plants absorb nutrients. If conditions are too alkaline or acidic, your plants’ root system will be unable to use specific nutrients.

Every nutrient you add or subtract will increase or decrease the pH. For instance, if you use too much fertilizer, your soil is likely to experience pH issues followed by nutrient lockout rapidly. We recommend purchasing pH test strips to measure the pH of your soil and water regularly.

What Are Mobile and Immobile Nutrients?

A significant number of novice growers are blissfully unaware that there are ‘mobile’ and ‘immobile’ nutrients, and there are also primary, secondary, and micronutrients. The difference between mobile and immobile nutrients depends on whether or not they can be translocated once assimilated by the marijuana plant.

A mobile nutrient can move from one part of the plant to another as and when needed. For instance, if a plant has a deficiency of a mobile nutrient, parts of it that have accumulated in old leaves move to new leaves to make up for the shortfall. This is why the first sign of any mobile nutrient deficiency is normally seen in the oldest leaves at the plant’s base.

Immobile nutrients stay in the same place once they are assimilated by the plant. You will spot signs of immobile nutrient deficiency in young leaves near the top and outer branches of the plant.

Crucial Cannabis Nutrients and Deficiency Symptoms

Aside from the three primary nutrients that most growers know about (Nitrogen, Phosphorus, and Potassium), we also cover signs of a potential deficiency for several essential nutrients.

Zinc (Immobile)

Your marijuana plants require zinc for sugar and protein production. This nutrient is also crucial for the formation and retention of chlorophyll and is necessary for strong stem growth. Zinc deficiencies in marijuana are relatively common and manifest in significant structural changes in your plant.

You will see twisted leaf blades on the plant’s new growth, while the veins of the leaves turn yellow. In some instances, you will see an extremely pale-looking plant. During the flowering stage, the plants’ buds become misshapen and twisted. A lack of zinc can result in a brittle plant. In general, zinc deficiency is also linked to a lack of iron and manganese. As a result, we recommend purchasing a micronutrient mix of all three.

Zinc Deficiency Symptoms

  • The leaves of the plant turn 90 degrees sideways.
  • The tips of the leaves become ‘burned’ and discolored, with brown spots arriving shortly afterwards.
  • New growth shows signs of interveinal chlorosis.

Molybdenum (Mobile)

Your marijuana plants only need a tiny amount of molybdenum, which means a deficiency in this micronutrient is rare. It plays a role in a pair of important enzyme systems which convert nitrate to ammonium.

Molybdenum Deficiency Symptoms

  • The middle leaves begin to turn yellow.
  • The shoots begin twisting, and there might be a red discoloration at the tips of the leaves.
  • Occasionally, the leaves of your plants curl up before dying and dropping.

Manganese (Immobile)

Manganese deficiencies are relatively rare in marijuana plants. They are typically found in conjunction with zinc and iron deficiencies. This nutrient is important for creating nitrates and also for production of chlorophyll. High soil pH or iron excess are also possible causes.

Manganese Deficiency Symptoms

  • Begins with interveinal chlorosis in new growth which spreads to older leaves.
  • The areas around the places where the plant is yellowing remain green.

Iron (Semi-Mobile)

Your marijuana plants require iron to assist with chlorophyll production and reduce and assimilate nitrates and sulphates. Iron deficiency can be caused by excess levels of copper, zinc, or manganese.

Iron Deficiency Symptoms

  • Young leaves and new shoots show a lighter green color than is normal.
  • Chlorosis spreads to other leaves.
  • These leaves become necrotic and eventually die.

Copper (Semi-Mobile)

Although your marijuana plants only need copper in trace amounts, it is important in the reduction of oxygen while aiding the plant’s carbohydrate metabolism and nitrogen fixation. As your plants only require a tiny amount, it is relatively rare to see copper deficiencies.

However, as it is important for reproduction and maturity, you must give your plants something to help replenish its copper supplies. Copper fungicides can help to re-adjust copper levels in the soil.

Copper Deficiency Symptoms

  • Necrosis in young leaves.
  • A copper-like or bluish gray color at the tips of the leaves.
  • Limp flowers, leaves, and other parts of the plant.

Sulfur (Semi-Mobile)

Although sulfur deficiencies are uncommon, they can occur if your fertilizer or soil doesn’t already have enough of it. Sulfur is an essential nutrient because it helps plant respiration, along with the synthesis and breakdown of fatty acids. If your soil or water has an excessively high pH, it could result in the loss of phosphorus, which is a major cause of sulfur deficiency.

Sulfur Deficiency Symptoms

  • Newer leaves begin to turn lime green, then yellow.
  • Stunted growth with narrow and brittle leaves.
  • Slow and weak flower growth with reduced potency.

Magnesium (Mobile)

Magnesium is one of the most important secondary nutrients. It is rare to experience a magnesium deficiency when you grow weed outdoors. However, it is more common when you grow indoors or if you use a soilless medium. It is a crucial player in the production of chlorophyll, and you must infuse your plant with magnesium immediately if you spot signs of deficiency.

Marijuana plants use magnesium in very high amounts, so if you believe your plants aren’t getting enough, use Epsom salts to deal with the issue. Make sure you distinguish between an iron and magnesium deficiency or else you could end up over-fertilizing your plants.

Magnesium Deficiency Symptoms

  • The trouble with magnesium deficiency is that you’re unlikely to spot any signs for 3 to 6 weeks after it has started. At this stage, you’ll notice the veins of older leaves becoming yellow, with rust spots.
  • Eventually, symptoms move through your whole plant with larger spots visible in the interveinal areas, along with the margins and tip of the leaves.
  • The plant will look sick, and leaves will start to curl up, die and fall off.
  • You will find that the signs of deficiency speed up during the flowering stage, which leads to a diminished harvest.

Calcium (Immobile)

Your marijuana plants need calcium as it is a crucial aspect of cell integrity and overall growth. Calcium helps with the flow of nitrogen and sugars throughout your plants. It is unusual to experience a calcium deficiency when plants are grown outdoors. However, it can happen when you grow your weed in plant mixes.

There are also certain types of water which don’t include large amounts of calcium; this makes them a poor choice if using a hydroponic system. You can treat a deficiency by using a calcium-rich substance such as lime.

Calcium Deficiency Symptoms

  • The plant’s development slows, and the young leaves begin to turn a darker green color.
  • The rate of flower production slows significantly.
  • The plant’s root tips will wither and die. As a result, your crop’s yield is reduced.
  • Large necrotic blotches on leaves that have become dark green.

Potassium (Mobile)

Potassium is one of the ‘big three,’and it aids the production and movement of carbohydrates and sugars. It also aids cell division and helps with water uptake, root growth, and transpiration. In essence, no potassium means no plant growth!

Despite its importance, potassium deficiencies are common. If you use a natural fertilizer such as bat guano, please note that potassium is the least abundant nutrient of the big three. Fixing major deficiencies requires a water-soluble fertilizer high in potassium.

Potassium Deficiency Symptoms

  • Potassium deficiency is deceptive because it makes it seem as if your plants are growing tall and vigorous at a glance. However, the bottom leaves could be dying.
  • Overly green leaves with rusty brown tips.
  • Dehydration, leaf burn, and the curling of younger leaves.
  • Weak plants at high risk of being attacked by pests, or stricken by disease.

Phosphorus (Mobile)

It is fairly unusual for marijuana plants to exhibit a phosphorus deficiency. One of the main reasons involves the pH of the water or growing medium going above 7.0. Your plants need phosphorus for photosynthesis, and it also to help the release of stored energy in carbohydrates.

If you allow a phosphorus deficiency to run amok, the effects could be devastating. Your plants will experience stunted growth, poor yields, and low resin production when they become mature. Make sure you use a fertilizer with a high amount of phosphorus or a bloom fertilizer.

Phosphorus Deficiency Symptoms

  • Slow growth and dark leaf colors.
  • Once the phosphorus deficiency threatens to get out of hand, upward and outward growth almost grinds to a halt. Dead spots will appear on petioles, and the plants’ leaves will curl and drop.
  • It is also possible that leaves will turn dark bronze.

Nitrogen (Mobile)

Although nitrogen is one of the most common nutrients in cannabis, and growers are aware of its importance, nitrogen deficiency is common. It plays a significant role in most plant functions including amino acid production and photosynthesis. Although your plants need nitrogen throughout their life cycle, it is especially important during the vegetative stage.

You can correct a deficiency by purchasing fertilizer with the right NPK ratio. Quick treatments include urine and bat guano. If you spot a nitrogen deficiency, act fast because your plant’s yield will be significantly affected otherwise.

Nitrogen Deficiency Symptoms

  • The plant’s older mature leaves will become lighter in color and eventually turn yellow. It is especially noticeable near the bottom of the plant.
  • A failure to treat the initial nitrogen deficiency will result in further yellowing of the plant. Eventually, the entire plant will be affected with discoloration and brown spots at leaf margins.
  • The leaves of your plants will start to curl and drop.
  • Although you need to ensure your plant gets lots of nitrogen during the vegetative stage, make sure it continues to get a reasonable amount during flowering. Otherwise, the plant will flower earlier, exhibit fewer bud sites, and yield less potent marijuana.

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