Plant problems · Nutrients · Any stage · Act this week
Magnesium deficiency
What you see
- Yellowing between the veins of older and middle leaves while the veins stay green
- Leaves can look marbled, then the yellow parts turn rusty or brown
- Tips and edges may curl up
- Common in coco, with RO water and in early flower
Why it happens
Magnesium is mobile, so the plant moves it from old leaves to new ones. Soft water, a pH below 6.0 in soil, or too much potassium or calcium compete with it.
What to do
- Add a calcium and magnesium supplement at the label dose
- For a fast fix, spray a weak Epsom salt solution (about 1 teaspoon per litre) on the leaves with the lights off, in veg only
- Correct the pH (soil 6.0 to 7.0, coco and hydro 5.8 to 6.2)
Next time
- Use cal mag with coco and RO water
- Do not overdose potassium in flower
Easy to confuse with
- Nitrogen deficiency: Lower, older leaves turn pale green, then evenly yellow from the tip inwards
- Potassium deficiency: Leaf edges and tips turn yellow, then brown and crispy, starting on older leaves
- Iron deficiency: The newest leaves turn pale yellow while their veins stay green
Not sure?
Take a photo of a middle leaf held up against the light, so the veins show and ask the Grow Doctor, or send it to the grow companion on Telegram.