Problem: A cannabis iron deficiency shows up first on bright yellow new leaves. It can also appear with other nutrient problems. Iron deficiency is often caused by pH issues, but stress can also play a role.
The main symptoms of a cannabis iron deficiency are:
- Newest leaves are completely yellow when they first grow in
- The bright yellow (almost white looking) color on new growth is the signature sign of an iron deficiency.
- Sometimes the affected yellow leaves are so damaged they’re beyond recovery. Other times the yellow parts of the leaves may begin to turn green as the plant continues to grow, starting from the tips and moving in toward the base of each leaf
- Eventually an entire leaf can become green and relatively healthy looking, even though it started out completely yellow from an iron deficiency. The ability of yellow leaves to eventually turn green is another signature of an iron deficiency, because for most other nutrient deficiencies any yellow leaves can’t truly turn green again.
A cannabis iron nutrient deficiency can look similar to a magnesium deficiency. But an iron deficiency affects newer/upper/inner leaves. A magnesium deficiency affects older/lower leaves.
The following severe iron deficiency was caused by using too much pure chicken manure as fertilizer. Remember, a little bit of manure goes a long way! Chicken manure raises the pH of soil, leading to iron deficiency. It also blocks iron uptake by the roots.
After adding chicken manure and watering, the plant showed bright yellow leaves. These leaves quickly dried up and died. The plant had an iron deficiency, but the soil had enough iron. The problem was the plant couldn’t get the nutrients because of nutrient lock-out.
Grower needs to dig up the manure and replant with good soil.
Solution For Cannabis Iron Deficiency
Note: Stress can cause a cannabis iron deficiency. The plant might get better after the stress goes away.
1.) Adjust pH to Correct Range
Most iron deficiencies come from too-high pH at the roots. Iron gets locked out at high pH, especially above 7.0. This is more common in soil or coco coir than in hydro.
If you suspect your growing cannabis plant has an iron deficiency due to too-high pH, flush your system with clean, pHd water. This will remove any nutrient salts that may be affecting the uptake of iron and help restore pH to the proper levels..
- In soil, iron is best absorbed by the roots in the 6.0 6.5 pH range (although its generally recommended for soil growers to keep pH in the 6.0-7.0 range, iron tends to get locked out when the pH is higher, especially above 7.0)
- In coco coir or hydro, iron is best absorbed by the roots in the 5.5 6.5 pH range
2.) Give the Right Nutrients
Most cannabis growers dont need to add more iron in response to an iron deficiency!
In fact, most growers have already given enough iron to their plants. This is because iron is found in most tap water. If you’re using quality soil or cannabis-friendly nutrients, you probably don’t need to add more iron.
Iron deficiency symptoms caused by true lack of iron are more likely to appear when using heavily filtered or reverse osmisis (RO) water. This is because any iron has been removed. Other nutrient problems, like calcium and magnesium issues, or too much copper, can also cause iron deficiency symptoms.
If you think you have iron deficiency, even with the right pH, try flushing your system. Use clean, pHd water. You can do this with your regular nutrients ) and add a supplement with Iron, Calcium and Magnesium.
Cannabis likes Calcium and Magnesium, and they help with Iron. A Calcium-Magnesium supplement, or ‘Cal-Mag’, can prevent these problems.
Cal-Mag works for Hydro, Coco Coir, and Soil. It’s good because it has extra Calcium and Magnesium. These are common deficiencies in cannabis, often with iron.
CaliMagic by General Hydroponics is what we use. But, other Cal-Mag products work well for growing cannabis too.
3.) Take Good Care of the Roots
Iron problems can happen if the roots are bad or if the plant is too wet. Good watering helps plants stay healthy and avoid problems.
4.) Watch for Recovery
After fixing things, wait a week or so to see if the iron deficiency clears up. New green growth means you’re on the right track!