How to Spot 8 Common Cannabis Plant Deficiencies by Leaf Symptoms

Leaves are the first place most nutrient problems show up. The trick is reading them correctly. Two questions narrow things down fast: where on the plant did the symptom start, and what does it look like? Below, we explain the old leaf versus new leaf rule, give a chart for eight common deficiencies, and lay out a step by step way to diagnose and fix them. It draws on University of Delaware Cooperative Extension, Alabama Cooperative Extension and South Dakota State University Extension. Those guides cover ornamentals, vegetables and field crops rather than cannabis, so use them as a general guide. Before you grow, check your state’s home grow law.

Step one: old leaves or new leaves?

University of Delaware Cooperative Extension explains that “the first step to visual identification of a nutrient deficiency is to determine where on the plant the symptoms are appearing.” A nutrient “is considered mobile if the plant is able to move it from one part of the plant to another as it is needed.”

UDel continues: “symptoms of N, P, K, and Mg deficiencies will manifest in the old growth because they are mobile, while symptoms of Ca, Cu, B, Fe, Mn, and Zn deficiencies will appear in the new growth because they are immobile.”

That one rule sorts most problems into two groups.

Step two: what do the symptoms look like?

UDel says the next step “is to determine the characteristics of the symptoms,” such as whether leaves are “chlorotic or yellow,” whether there is “necrotic or dead tissue,” and whether symptoms are on “the leaf margins or tips” or “interveinal (i.e., between the veins).”

The 8 deficiencies at a glance

The “where it starts” column follows UDel’s mobile and immobile groups. The cannabis descriptions are common grower observations, not Extension definitions. UDel’s immobile list also includes copper and boron. This chart covers eight common ones that growers most often check.

A closer look at the mobile four

Nitrogen. Often seen in veg, in common grower experience. Lower leaves pale evenly to yellow, then drop. Some yellowing late in flower is normal.

Phosphorus. Alabama Cooperative Extension describes early signs as “an abnormally dark green or reddish purple color along the edge of the lower plant leaves,” and notes that “cold temperatures retard root growth and reduce the phosphorus uptake in plants.” See our phosphorus guide.

Potassium. Edges and tips of older leaves turn yellow, then brown and crispy.

Magnesium. South Dakota State University Extension describes it as “interveinal chlorosis (leaf veins stay green while the regions between them turn yellow).” See our magnesium guide.

Check pH before you add anything

Many deficiencies are really lockouts. UDel warns that “when soil pH is too acidic, elements such as K, Ca, and Mg may exist in a chemical form that plant roots cannot absorb, even if these elements are present in sufficient amounts. Similarly, Fe, Mn, Zn, and B exist in forms that are unavailable to plants at alkaline pH.” UDel recommends a soil test before applying fertilizer, because it “can prevent the application of excess fertilizers.”

Calcium, iron, manganese and zinc on new growth

Problems that start at the top of the plant are often about uptake rather than supply. Iron, manganese and zinc become less available at high pH, so new leaves yellow between the veins even when the feed contains them. Calcium moves with water, so poor root health or very humid, still air can show up as spotted or distorted new growth. Fixing pH, roots and airflow often clears these up without extra nutrients.

How to diagnose and fix: step by step

1. Note where it started. Old leaves point to N, P, K or Mg. New leaves point to Ca, Fe, Mn or Zn.
2. Describe the pattern. Even yellowing, yellowing between veins, brown edges, spots or twisted growth.
3. Check runoff pH. Many soil growers aim for roughly 6.0 to 7.0 and coco growers roughly 5.8 to 6.2, which is common grower practice. Fix pH first.
4. Check roots and watering. Overwatered or rotting roots cannot take up nutrients. See our Pythium root rot guide.
5. Review your feeding. Too much of one nutrient can block another. Excess potassium, for example, can cause magnesium shortage, as SDSU notes.
6. Make one change at a time. Change pH or feed, not both plus a new additive. Otherwise you cannot tell what worked.
7. Watch new growth. Damaged leaves rarely recover. Healthy new leaves over the next week or two mean your fix is working.
8. Keep a log. Write down symptoms, pH, feed strength and changes with dates.

Deficiency or something else?

Not every yellow or spotted leaf is a nutrient problem. Light burn bleaches the leaves closest to the lamp. Heat stress can make leaf edges curl up. Overwatering makes leaves droop and yellow even when nutrients are fine. Pests such as spider mites leave tiny pale speckles, and fungal leaf spots often have rings or fuzzy growth. Before you change your feed, check light distance, temperature, watering and the undersides of leaves.

Safety notes

Wear gloves when handling concentrated nutrients and pH adjusters, and keep them away from children and pets. If you use any foliar spray, keep it off developing buds and follow the product label.

Troubleshooting

Several symptoms at once. UDel notes that when “more than one nutrient is deficient, visual symptoms may be misleading.” Start with pH and roots, which cause many problems together.

Yellowing at the top and bottom. Check pH and light. Light burn can bleach top leaves.

Spots with rings or fuzzy growth. That may be disease, not a deficiency. Remove affected leaves, bag them and throw them away. Never use moldy buds.

Brown tips on many leaves after feeding. Likely overfeeding. Water with plain, pH adjusted water and lower the strength.

Lower leaves yellowing in the final weeks. Usually normal fading before harvest.

Related guides

See our soil feeding schedule and how to revive sick cannabis plants.

Sources

• University of Delaware Cooperative Extension, Identifying Nutrient Deficiencies in Ornamental Plants. https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/identifying-nutrient-deficiencies-in-ornamental-plants/ (opened 2026-10-16)
• Alabama Cooperative Extension System, Phosphorus Basics: Deficiency Symptoms, Sufficiency Ranges, and Common Sources. https://www.aces.edu/blog/topics/crop-production/phosphorus-basics-deficiency-symptoms-sufficiency-ranges-and-common-sources/ (opened 2026-10-16)
• South Dakota State University Extension, Monitoring and Correcting Magnesium Deficiency in High Tunnels. https://extension.sdstate.edu/monitoring-and-correcting-magnesium-deficiency-high-tunnels (opened 2026-10-16)