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Plant health · Diagnosis

Diagnosis of nutrient deficiency and toxicity

This paper shows you how to read the symptoms on cannabis leaves from the position, color and shape. You will know how to find the difference between mobile and immobile nutrient deficiencies. You will also know how to find the difference between a deficiency, a toxicity and a pH lockout. Before you change your feed, you will know how to make sure of the diagnosis with a pH meter and an EC meter.

Plant health12 figures7 sources~14 min to read

In this paper

01 Purpose and scope 02 Definitions 03 Evidence and limitations 04 Leaf position and nutrient mobility 05 Deficiency, toxicity and pH lockout 06 pH targets for each substrate 07 Reference table of symptoms for each nutrient 08 How to make sure of the diagnosis with pH, EC and runoff 09 Troubleshooting 10 Expected results and limitations 11 References

Start here

Purpose and scope

A cannabis plant shows you the nutrients that it does not have in sufficient quantity, and the nutrients that it has too much of. It shows them through the color, the shape and the position of the symptoms on its leaves. This paper shows you how to read these signals with a method. Thus you find the cause, and you do not add fertilizer when it is not necessary.

The most important fact comes first: where a symptom shows on the plant is usually more important than the color of the symptom. A symptom shows on the old leaves at the bottom or on the new leaves at the top. If you use this one method, you decrease the list of possible causes to approximately half.

A nutrient is one of the approximately 17 chemical elements that a plant must absorb for growth^[8]. The nutrients that you change most frequently are nitrogen (N), phosphorus (P) and potassium (K). Other nutrients are calcium (Ca), magnesium (Mg), sulfur (S), and small quantities of micronutrients, for example iron and zinc.

Three different problems can have almost the same symptoms on a leaf. A deficiency is the condition when the plant does not have a sufficient quantity of an element. A toxicity is the condition when the plant has too much of an element. A pH lockout is the condition when the element is in the water, but the roots cannot absorb it. The primary task is to find the difference between these problems.

Figure 1. The plant shows its condition. Examine the position and the color of the leaf, and think of a possible cause. Then make sure of the cause with two measurements that have a low cost, before you make a change.

A yellow leaf does not always show a deficiency. The same color can have three causes that are very different.
Problem	Definition	The sign that identifies it
Deficiency	The plant does not have a sufficient quantity of an element	The green color decreases gradually. New growth has less green color.
Toxicity	The plant has too much of an element or salt	Dark green leaves with the claw, and tip burn
pH lockout	The element is in the water, but the roots cannot absorb it	Symptoms of a deficiency when the feed is correct

A leaf with damage does not become green again

Examine the new growth, not the old leaves, to know if the plant is in good condition again. A leaf that has damage does not become green again after you correct the cause. When a leaf shows damage, the plant did not have a sufficient quantity of the nutrient for some days. A diagnosis from the symptoms is not fast.

List of terms

Definitions

Before you do a diagnosis, you must know some terms that growers use frequently. The definitions are easy. Read this section one time, and go back to it when necessary.

MacronutrientAn element that the plant uses in large quantities: N, P, K, Ca, Mg, S.

MicronutrientAn element that the plant uses in small quantities: iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo).

Mobile nutrientA nutrient that the plant can remove from an old leaf and send to new growth when the supply is not sufficient. The nutrients are N, P, K and Mg.

Immobile nutrientA nutrient that stays in the position where the plant first puts it, and that the plant cannot move. The nutrients are Ca, S, Fe, Mn, Zn, B, Cu and Mo.

ChlorosisChlorosis is the condition when a leaf becomes yellow because the green chlorophyll decreases. Interveinal chlorosis is chlorosis between the veins, while the veins stay green. This symptom is very frequent, and it is easy to identify.

NecrosisNecrosis is dead tissue that is brown and dry. The tissue does not become green again.

pHpH is a scale from 0 to 14. It shows if the water in the root zone is acid or alkaline. The pH has an effect on the nutrients that dissolve in the water and that the plant can absorb.

EC (electrical conductivity)EC is a measurement of the quantity of dissolved salt or fertilizer in the water. It shows the strength of the feed. PPM is the same measurement in different units.

RunoffRunoff is the water that drains from the bottom of the pot. You can measure the runoff to know the condition in the root zone.

Figure 2. Each usual element is a mobile nutrient or an immobile nutrient. As a result, the old leaves or the new leaves show the symptoms first.^[7]

Terms in the facility Nano Banana 2

Diagram. Mobile nutrients show a deficiency first on the leaves at the bottom of the plant. Immobile nutrients show a deficiency on the new growth at the top.

Diagram. An EC that is too high increases the concentration of salts. This stress on the uptake can cause a deficiency, or the same symptoms as a deficiency.

Quality of the information

Evidence and limitations

Three types of information

We want each paper to be correct. Thus we examine each paper for information that is not solid. This information comes from the view of one grower, from a small number of sources, or from grower methods that have no controlled test. We identify this information, and we do not show it as solid.

Frequently there is no paper for the decision that you must make. Then we use the reports of other growers and the methods that work in the rooms that we know. This information can help you, but it is not the result of a laboratory test. Use the methods that work for your plants, for your room and for your meters. If a table does not agree with your crop, use the data from your crop and record the difference.

Solid

Tests of plants, specifications or many sources that agree show that the information is correct

The position of a symptom on the plant, for a mobile nutrient or an immobile nutrient, is a good first step to find the cause.
A pH lockout, too much water and light stress can show the same symptoms as nutrient problems.

Grower method

Many growers use this method in their rooms. Start with it, then change it for your room.

Guides to the symptoms of N, P, K, Mg, Ca and Fe on cannabis.

Weak

The view of one grower, a small number of sources, one test, or a method that works in one room

A visual identification of the problem as a result that is as sure as a laboratory test, with no test of tissue or substrate.
An atlas of micronutrients with missing parts. Be more careful with Zn, B, Mn, Cu and Mo.

If you find an error, make a report. We will correct it. Make the report on GitHub, with the name of the paper and the information that is incorrect. If you have a source, include it: Make a report of an accuracy problem. The regulations, labels and licenses of your area always override each procedure in these papers. The label weak in a paper shows the points where the risk of an error is highest.

Primary fact 1

Leaf position and nutrient mobility

When a plant does not have a sufficient quantity of a mobile nutrient, the plant removes the element from its old leaves. Then the plant sends the element to the new growth at the top. The damage shows first at the bottom of the plant, and then at higher leaves. Immobile nutrients stay in the cell walls where the plant puts them, and the plant cannot remove them. Thus, when the plant does not have a sufficient quantity of an immobile nutrient, the new growth at the top shows the damage first. The old leaves stay in good condition.^[2]

This one method decreases the list of possible causes to approximately half before you examine the color.

Chlorosis and then necrosis on the bottom leaves or the old leaves, that continue to the higher leaves, are a sign of a mobile nutrient. The nutrient is nitrogen, phosphorus, potassium or magnesium.
New leaves at the top with a twisted shape, with less green color, or with bent tips are a sign of an immobile nutrient. The bottom leaves are in good condition. The nutrient is calcium, sulfur, iron, zinc, manganese or boron.
Equal symptoms on all the plant, or damage on the two ends at the same time, are not a sign of one deficiency. They are a sign of a pH lockout, a root problem or stress from the environment.

Figure 3. The symptoms of mobile nutrients show on the old leaves at the bottom. The symptoms of immobile nutrients show on the new growth at the top.^[1]

Compare the symptoms with the growth stage

At the end of flowering, the plant moves the nitrogen to the buds. As a result, it is usual that the green color of the leaves decreases from the bottom up. The same symptom is usual at week 7, and it is a problem at week 2. Thus the week of the growth stage is necessary information before you make a change.

Primary fact 2

Deficiency, toxicity and pH lockout

The most frequent error of a new grower is this. The grower sees yellow leaves and thinks that the plant does not have sufficient nutrients. Then the grower adds more fertilizer. More fertilizer makes a toxicity or a lockout much worse. A toxicity shows as dark green leaves with the claw, and tip burn. This symptom is the opposite of leaves with less green color.

In a pH lockout, the nutrient is in the water at the roots, but the roots cannot absorb it. The cause is the pH, and the uptake stops when the nutrient is in the water. Only a correction of the pH lets the roots absorb the nutrient again.

Deficiency: The green color decreases gradually and the leaves become yellow. The new growth is smaller. After some time, the leaves fall from the plant. The plant has less and less green color.
Toxicity (too much feed): The leaves become dark green and glossy. The tips have tip burn: they become brown and bend. If the nitrogen is very high, the leaf tips bend down. This shape is the claw.^[5]
pH lockout: The usual symptoms of a deficiency show, frequently of iron, or of calcium and magnesium. They show when the feed is correct, because the pH is not in the range where the roots can absorb the nutrients.^[6]

One symptom has three causes. For almost all of these problems, more fertilizer is not the correct first task.
Symptom that you see	If it is a deficiency	If it is a toxicity	If it is a lockout	First task
Yellow leaves	The plant does not have a sufficient quantity of an element	Too much salt. The roots do not get sufficient nutrients	The pH stops the uptake	Measure the pH before you apply feed
Brown tips that are dry	Not sufficient potassium (edges)	Nutrient burn, or damage from salt	Not sufficient micronutrients, frequently because of the pH	Measure the EC of the runoff
Dark green leaves with the claw	Not frequent	Too much nitrogen	Not usual	Decrease the feed strength

Figure 4. The correct condition is the middle range. A deficiency is one failure mode: the leaves have less green color and they fall from the plant. A toxicity is the opposite failure mode: the leaves are dark green and have the claw. If you change the feed in the incorrect direction, the problem becomes worse.

Always measure the pH first

Before you apply a treatment for a deficiency, measure the pH. If the pH is not in the range, correct the pH. Then monitor the plant again for some days, before you think that the plant does not have a sufficient quantity of a nutrient. A pH that is not in the range causes lockout when the feed is correct.^[6]

Diagram. pH lockout causes most deficiencies. The nutrient is in the root zone, but the plant cannot absorb it when the pH is not in the band.

Primary fact 3

pH targets for each substrate

Each nutrient dissolves, and the plant can absorb it, only in one range of pH. If the pH in the root zone is not in the correct range, some nutrients do not stay dissolved at the same time. Then the plant does not have sufficient nutrients, but the substrate contains the nutrients. A correct pH prevents more deficiencies than a fertilizer corrects.

The correct target pH is different for each substrate. Soil has a buffer, and its target range is higher. Coco and hydroponics have no buffer. Thus you must adjust the pH with high precision.

Figure 5. The areas with color show the ranges where the roots can absorb the nutrients. The range for soil is higher by a small quantity, and it is wider. The ranges for coco and hydro are lower and have a smaller width.^[6]

Soil is the substrate that has the highest tolerance for pH errors. Coco and hydro have no buffer. Thus you must measure the pH much more frequently.
Substrate	Target pH	Good range	Frequency of measurement	Buffering
Soil	6.0-7.0	6.2-6.8	Each week	High. Small errors do not cause a problem.
Coco	5.5-6.5	5.8-6.2	With each feed	None
Hydro	5.5-6.5	5.8-6.2	Each day	None

The direction of pH drift shows the nutrients in lockout

More than approximately 6.5 in coco or hydro: iron, manganese, zinc and boron do not stay dissolved. Chlorosis in the new growth is possible, with the symptoms of a micronutrient deficiency.^[6]
Less than approximately 5.5: calcium, magnesium and phosphorus are in lockout.
A small change of the pH in the range (for example 5.8-6.2) gives each nutrient a time when the plant can absorb the maximum quantity. But keep the pH in the range for your substrate.

Reference for use at the plant

Reference table of symptoms for each nutrient

Use the reference table at the plant. For each nutrient, the table gives the position on the leaf and the color or shape of the symptom. It also gives the one sign that shows the difference from problems with almost the same symptoms. Use the method of old leaves and new leaves, from the section before, to find the correct row quickly.

The table of leaf symptoms. First the position, then the color or shape, then the sign that shows the difference.
Nutrient	Mobile?	Position	Color or shape	The sign that shows the difference
Nitrogen (N)	Mobile	Old leaves at the bottom	All the leaf has less green color equally, then it becomes yellow and falls from the plant	The most frequent deficiency. Too much N gives dark green leaves with the claw.
Phosphorus (P)	Mobile	Old leaves at the bottom	Dark leaves, matt, with bronze, gray or purple patches	Some cultivars are purple without a deficiency. Do not use only the stems to make a decision.
Potassium (K)	Mobile	Old leaves at the bottom	Tip burn: the tips and the edges are brown and dry. The middle of the leaf stays green.	The damage is at the edges. Nitrogen gives a fade of all the leaf.
Magnesium (Mg)	Mobile	Old leaves at the bottom	Interveinal chlorosis. The veins stay green.	Starts in the middle of the leaf, and goes slowly to the other parts of the leaf
Calcium (Ca)	Immobile	New leaves at the top	New growth with a twisted shape and brown patches	A change of shape, not only of color
Sulfur (S)	Low mobility	New leaves at the top	New leaves with less green color, or yellow	All of the new leaf has less green color. It is not interveinal chlorosis.
Iron (Fe)	Immobile	New leaves at the top	Interveinal chlorosis with a very strong yellow color. The veins stay green.	Very frequent when the pH is high. The symptom is on the top leaves.

Two of these nutrients give almost the same symptoms, and these symptoms cause errors for new growers frequently. Magnesium and iron cause interveinal chlorosis with green veins.^[4] The position shows the difference. Magnesium causes it on the old leaves at the bottom. Iron causes it on the new growth at the top.

Figure 6. Magnesium deficiency is interveinal chlorosis on the old leaves. Iron deficiency is the same symptom on the new growth.^[4]^[1]

Figure 7. Nitrogen and potassium are the largest part of the uptake in flowering. Thus their deficiencies are the deficiencies that you will see most frequently.^[3]

The steps

How to make sure of the diagnosis with pH, EC and runoff

A diagnosis is a loop, and not a decision without data. Examine the leaves. Then make sure of the cause with two meters that have a low cost, before you make a change. Measure the EC and the pH of the input and of the runoff from the pot. The measurements show if the root zone has a deficiency, a toxicity or a lockout.

1
Step 1: measure the input pH and EC
Make sure that the feed pH is correct for your substrate: 5.8-6.2 in coco or hydro, approximately 6.5 in soil. Make sure that the strength is correct for the growth stage.
2
Step 2: measure the runoff
In coco, the runoff EC is usually approximately equal to the input EC. If the runoff EC is more than the feed EC by approximately 0.3–0.5 mS/cm (or more) for some days, the salt increases. The feed is too strong. Plants with less green color and a low runoff EC show that the feed is too weak.
3
Step 3: select the correction for the cause
If there is a lockout or too much salt, flush the root zone with water that has the correct pH. Use water with no nutrients, or with a low feed strength. Do this until the runoff EC is usual, and then start the feed again. If the feed is too weak, increase the EC gradually. If one nutrient is not sufficient, correct the pH first. Then add that nutrient.
4
Step 4: monitor the new growth
Examine the new leaves, and not the leaves with damage, for 5-10 days. The new leaves show if the plant is in good condition again. A leaf with damage does not become green again.

Figure 8. The target EC increases from the seedling stage to the peak of flowering, and then it decreases for the end of the crop. Seedling: approximately 0.4-0.8 (approximately 250-400 PPM). Vegetative growth: 1.0-1.8. Flowering: 1.6-2.4, that increases to 2.4-3.0 at the end of flowering.

The runoff EC is an indicator of salt

The runoff EC in coco is usually approximately equal to the input EC. If the runoff EC is more than the feed EC by approximately 0.3–0.5 mS/cm for some days, the salt increases faster than the plant uses it. The correct task is a flush. More feed is not correct.

Troubleshooting

Most of the deficiencies that new growers find are pH lockout, too much water, or damage from light. These problems have the symptoms of a deficiency. If you know these problems, you do not add fertilizer to a plant that has too much water, damage from light or a lockout. When you are not sure, make only one change at a time and wait.

The five problems. Each problem has the symptoms of a deficiency, and each problem becomes worse if you add feed.
Problem	Same symptoms as	Sign that shows it	Examine this, not the feed
Too much water	Nitrogen toxicity (leaves bend down, with the claw)	The substrate is wet, and the plant uses water slowly	The moisture of the soil, the drainage of the pot
Root rot	Many deficiencies at the same time	Brown roots that are soft and wet, and an unwanted odor	The condition of the roots, the oxygen at the roots
Stress from light or heat	Nutrient burn, or a deficiency	Damage only on the top of the canopy, near the lamp	The distance to the light, the canopy temperature
pH lockout	A deficiency of iron, or of calcium and magnesium	Symptoms of a deficiency when the feed is correct	The pH of the input and of the runoff
Nutrient antagonism	A deficiency of calcium and magnesium	It occurs after too much of one element	If you added too much K

Nutrient antagonism is the problem that is not easy to find. Too much of one element stops the uptake of a different element at the uptake sites of the root. Too much potassium decreases the uptake of calcium and magnesium. Thus a deficiency of calcium and magnesium can be a result of too much potassium. Because of this, too much of one element in the feed makes the problem worse.^[9]

Figure 9. Too much water and stress from light give the same symptoms as nutrient problems. Thus a deficiency of one nutrient is the last diagnosis, not the first.^[9]

The limits of diagnosis

Expected results and limitations

A diagnosis gives you a list of possible causes with confidence. It is not as accurate as a laboratory test. The symptoms that you see are almost the same for some problems, and only a test of the tissue or of the substrate is accurate.^[1] Leaves with damage do not become green again. Thus the correct result is new growth in good condition, not damaged leaves that become green again.

You will find the correct type of problem (mobile or immobile, and deficiency, toxicity or lockout) more frequently than the correct element. This information is usually sufficient to make a correct change.
After you make a correct change, examine the new growth. The new growth is in good condition in a maximum of approximately 5-10 days. The leaves that have damage do not become green again. You can keep them on the plant or remove them.
One correct procedure for the measurement of pH and EC prevents most nutrient problems. If you apply a correction for each element, the procedure is not correct.
For crops with a high value, or for commercial crops, use a test of the leaf tissue or of the substrate. The test makes sure of the diagnosis when the symptoms can have more than one cause. Do not make a decision only from the symptoms that you see.

Figure 10. The procedure with a low cost on the left prevents most of the tasks with a high cost on the right. A stable pH and EC procedure is much less work than the correction of a problem.

Prevent problems before the diagnosis

The visual method is a fast first check. It is not the last diagnosis. Most problems do not occur if the pH and the feed strength stay stable. Thus make the procedure first, and use the diagnosis as a second check.

Next, make the two procedures correct, because they prevent most of these problems. Read the pH management paper. Then read the nutrient mixing paper, to make the feed correct from the start.

References

Cockson, P., Landis, H., Smith, T., Hicks, K., & Whipker, B. E. (2019). Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences, 9(20), 4432. https://doi.org/10.3390/app9204432 https://www.mdpi.com/2076-3417/9/20/4432
Maillard, A., Diquelou, S., Billard, V., Laine, P., Garnica, M., Prudent, M., Garcia-Mina, J.-M., Yvin, J.-C., & Ourry, A. (2015). Leaf mineral nutrient remobilization during leaf senescence and modulation by nutrient deficiency. Frontiers in Plant Science, 6, 317. https://doi.org/10.3389/fpls.2015.00317 https://pmc.ncbi.nlm.nih.gov/articles/PMC4429656/
Bevan, L., Jones, M., & Zheng, Y. (2021). Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis. Frontiers in Plant Science, 12, 764103. https://doi.org/10.3389/fpls.2021.764103 https://pmc.ncbi.nlm.nih.gov/articles/PMC8635921/
Morad, D., & Bernstein, N. (2023). Response of Medical Cannabis to Magnesium (Mg) Supply at the Vegetative Growth Phase. Plants, 12(14), 2676. https://doi.org/10.3390/plants12142676 https://pmc.ncbi.nlm.nih.gov/articles/PMC10386616/
Saloner, A., & Bernstein, N. (2020). Response of Medical Cannabis (Cannabis sativa L.) to Nitrogen Supply Under Long Photoperiod. Frontiers in Plant Science, 11, 572293. https://doi.org/10.3389/fpls.2020.572293 https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.572293/full
Neilsen, D., Neilsen, G. H., Sinclair, A. H., & Linehan, D. J. (1992). Effect of rhizosphere pH on the availability and uptake of Fe, Mn and Zn. Plant and Soil, 145(1), 45-50. https://doi.org/10.1007/BF00009540 https://link.springer.com/article/10.1007/BF00009540
Liu, G., Hanlon, E., & Li, Y. (2017). Movement of Plant Nutrients (HS1373). UF/IFAS Extension, University of Florida. https://edis.ifas.ufl.edu/publication/HS1373 (source not from a journal, for example from a manufacturer) https://edis.ifas.ufl.edu/publication/HS1373
Hawkesford, M., Horst, W., Kichey, T., Lambers, H., Schjoerring, J., Skrumsager Moller, I., & White, P. (2012). Functions of Macronutrients. In P. Marschner (Ed.), Marschner's Mineral Nutrition of Higher Plants (3rd ed., pp. 135-189). Academic Press. https://doi.org/10.1016/B978-0-12-384905-2.00006-6 https://www.sciencedirect.com/science/article/pii/B9780123849052000066
Fageria, V. D. (2001). Nutrient interactions in crop plants. Journal of Plant Nutrition, 24(8), 1269-1290. https://doi.org/10.1081/PLN-100106981 https://www.tandfonline.com/doi/abs/10.1081/PLN-100106981

Each citation in the paper, for example [1], refers to an item in this list. Each item is a primary source or an instruction from an authority, unless the item shows a different type. The results of cannabis tissue culture change much with the genotype. Before you use the dilutions, hormone doses and local regulations, make sure that they agree with the primary sources.