Nutrient deficiencies in cannabis: How to spot and address them

As a cannabis cultivator, you want to grow the healthiest cannabis plants with the highest yields possible. Nothing slows down this growth goal faster than a nutrient deficiency. In serious cases, cannabis plants will be more vulnerable to attacks from pests and mold. The most severe nutrient deficiencies ultimately result in the death of the plant. Fortunately, there are ways to identify and treat different types of nutrient deficiencies in your marijuana plants and encourage new growth.

cannabis plant nutrient deficiencies
There are ways to identify and treat different types of nutrient deficiencies in your marijuana plants and encourage new growth.
Photo by: Gina Coleman/Weedmaps

In this guide to cannabis nutrient deficiencies, you will learn how to pinpoint and resolve deficiency symptoms to keep your cannabis plants in top condition.

What causes nutrient deficiencies in marijuana plants?

Improper pH levels are a common cause of nutrient deficiencies in marijuana plants. The soil should not be too acidic nor too alkaline but rather a perfect balance for the plant. Marijuana does best in a slightly acidic environment. Aim for a range of 5.8 to 6.8 soil pH, with the midpoint of 6.3 considered optimal. For hydroponic solutions, the ideal pH falls between 5.5 and 6.5 with the optimal level differing depending on the product. But it's not just the soil pH level you need to monitor. Make sure to test the pH levels of your water as well.

Signs of a healthy cannabis plant

What does a healthy cannabis plant look like? The first word that comes to mind is green. All plants exhibit good health through hydrated, abundant, bright green shoots and leaves. To assess the health of your cannabis plants, look for several key indicators:

  • Green leaves free of spots and other discoloration, such as yellowing between leaf veins
  • Sturdy plant stature with no apparent drooping
  • Prolific, resinous buds at harvest time
healthy marijuana plant
All plants exhibit good health through hydrated, abundant, bright green shoots and leaves.
Photo by: Gina Coleman/Weedmaps

If your plants exhibit these three key indicators of good health, it is unlikely that a nutrient deficiency exists. On the other hand, these warning signs can tell you if a plant is lacking any essential nutrients.

Signs of nutrient deficiencies

Plants can't tell us what's wrong through words, but luckily cannabis deficiencies will present themselves in several observable ways. Here are three general nutrient deficiency symptoms to watch out for:

  • Discoloration: Lightening and/or yellowing of leaves, particularly near the base of the plant, can signal a nutrient deficiency.
  • Drooping: Leaves will curl, droop, and ultimately drop in many types of cannabis nutrient deficiencies.
  • Low yield: Above all, a low yield of flowers will tell you (after it's too late) that your plants are nutrient-deficient. But you can prevent this unwanted outcome by familiarizing yourself with the different types of marijuana nutrient deficiencies and the symptoms to search for in each one.
wilting marijuana plant
Cannabis deficiencies will present themselves in several observable ways, such as discoloration, drooping, and a low yield of flowers.
Photo by: Gina Coleman/Weedmaps

Types of cannabis nutrient deficiencies

Cannabis plants require many of the same nutrients to thrive that humans do. Just like us, they need calcium, iron, and potassium. But marijuana plants' deficiencies will present in different ways. Whereas a lack of calcium can make our bones brittle, such a deficiency can completely stunt the growth of cannabis plants and ultimately lead to death. Yellowing leaves are a universal sign of vitamin and mineral deficiencies, but each nutrient may cause additional symptoms to appear.

Here are the top 10 nutrients that cannabis plants need for optimal health along with signs of deficiency.

1. Potassium: Potassium keeps plants flowering and wards off pests, such as spider mites. Dull leaves are one of the most obvious signs of a potassium deficiency, but so are brown spots and brownish leaf tips that appear burnt. 

2. Phosphorus: Necessary for photosynthesis, phosphorus also contributes to overall plant growth and resin production. In addition to the tell-tale yellowing, plants with a phosphorus deficiency may have a dark purple hue and blackish spots on the leaves. 

3. Nitrogen: As the primary element of the NPK (nitrogen, phosphorus, and potassium) powerhouse of nutrients, nitrogen is the most common deficiency in marijuana plants. A shortage presents as yellowing of the entire plant, along with curled leaves and scant buds.

4. Magnesium: Magnesium is essential for adequate energy absorption from light as well as for creating carbohydrates and sugars that yield flowers. Observable as many as six weeks after development, a magnesium deficiency causes rusty spots to form on the leaves and, ultimately, for the whole plant to droop. 

5. Calcium: Without calcium cells cannot grow sufficiently nor can vital nitrogen and sugars circulate through the plant. If cannabis has a calcium deficiency, you'll notice curling lower leaves followed by withered root tips at an advanced stage. 

cannabis plant with yellow flowers
If cannabis has a calcium deficiency, you'll notice curling lower leaves followed by withered root tips at an advanced stage.
Photo by: Gina Coleman/Weedmaps

6. Sulfur: Sulfur is crucial for the development of potent oils and terpenes, many of which may offer therapeutic benefits after harvest. The symptoms of a sulfur deficiency are subtle, starting with pale green to yellow leaves and culminating with slow and limited flower production. 

7. Iron: Plants need ample iron for chlorophyll production and overall health. Look for yellowing between the leaf veins to gauge whether your cannabis is suffering from an iron deficiency. An iron deficiency is often the domino effect of other types of nutrient deficiencies, namely a lack of copper, manganese, and zinc. 

8. Copper: Since copper is needed only in trace amounts, a copper deficiency is rare but not unheard of. Look for dead spots on the leaf tips, along with a wilting and twisting of the entire plant to diagnose a copper deficiency. 

9. Manganese: As with copper, a manganese deficiency is uncommon. It can result from high iron or pH levels. The first signs of a manganese deficiency appear in new growth and spread to older leaves, resulting in dead spots on all the leaves. 

10. Zinc: A zinc deficiency is more common in cannabis than copper and manganese deficiencies and, again, high pH levels can be the culprit. Scrutinize the delicate leaf tips to determine if your plants have a zinc deficiency. The leaf tips will turn a burnt brown shade and eventually rotate 90 degrees to one side. 

What to do about nutrient deficiencies in cannabis

When it comes to nutrient deficiencies in cannabis, the best solution is prevention, which means providing your plants with the best quality soil and optimal lighting conditions from the beginning. But cultivating cannabis can be an experience in trial and error, especially for the beginner. So if your plants aren't in peak condition, here are some possible solutions.

  • Experiment with nutrient-rich potting soils and consider investing in a better quality soil if your budget allows. 
  • Test the pH levels of your soil and/or hydroponic nutrient solution to make sure they fall within the optimal range. 
  • Move your cannabis plants if too much or too little light could be an issue. 
  • Prune any damaged leaves to inhibit the spread of disease to new leaves.

A little extra TLC can go a long way in nursing a sick cannabis plant back to health and giving you a healthy harvest.

Was this article helpful? Give Feedback

{EMAIL}
has been subscribed!

The information contained in this site is provided for informational purposes only, and should not be construed as medical or legal advice. This page was last updated on September 8, 2020.