Magnesium deficiency
Interveinal yellowing of the older leaves — sharp green veins on a yellowing, then reddening, leaf — that works up the plant from the bottom.
- Nutrient type
- Secondary
- Mobility in plant
- Mobile
- Symptoms start on
- Old (lower) leaves
- Most at risk
- Sandy, acidic, high-K soils
Overview
Magnesium sits at the centre of every chlorophyll molecule, so a shortage bleaches the leaf between the veins while the veins themselves — still fed — stay a sharp green. The pattern is a green skeleton on a yellow leaf, and as it worsens the yellow tissue turns orange, red or purple and dries.
Magnesium is mobile in the plant, so when it runs short the crop pulls it out of the older leaves to keep the new growth going. That means the symptoms always start on the oldest, lowest leaves and climb upward — the opposite of iron and manganese, whose interveinal yellowing starts at the top. It is common on sandy, acidic and heavily-potassium-fertilised soils.
How to spot it
- The tissue between the veins of the older, lower leaves yellows while the veins stay green — a green net on a yellow leaf, starting at the bottom of the plant.
- As it worsens, the yellow areas turn orange, red or purple and the leaf edges dry and curl.
- The pattern climbs upward over time; the newest top leaves are the last to show it.
- In fruit crops (grapes, citrus, banana) heavy fruit load pulls magnesium to the fruit and worsens leaf symptoms as harvest nears.
Why it happens
- Sandy, light soils hold little magnesium and lose it to leaching under rain and irrigation.
- Acidic soils (low pH) are often low in magnesium as well as calcium.
- Heavy potassium fertiliser competes with magnesium at the root — a very common cause on intensively fertilised fruit and vegetable crops.
- A heavy fruit or tuber load drawing magnesium away from the leaves late in the season.
Confirm before you spend
- Interveinal yellowing on the OLD, lower leaves points to magnesium; the same pattern on the NEW, upper leaves points to iron or manganese instead. Direction settles it.
- Check whether you have been applying a lot of potash — a high-potassium, low-magnesium balance is a frequent, correctable cause.
How to correct it
- On acid soils, apply dolomitic limestone (dolomite) — it raises pH and supplies magnesium and calcium together.
- Where pH is fine, apply magnesium sulphate (Epsom salt) to the soil, or spray 1–2% Epsom salt on the foliage for a fast green-up of a standing crop.
- Rebalance potassium — if heavy potash use is starving the crop of magnesium, easing it off is part of the fix.
- For fruit trees and grapes, a foliar Epsom salt spray during fruit development is the usual practical correction.
Prevent it coming back
- Use dolomite rather than plain lime when liming acid, magnesium-poor soils, so you top up magnesium each time you correct pH.
- Keep the potassium-to-magnesium balance sensible rather than pushing potash alone, especially on sandy soils.
- Build organic matter to hold magnesium against leaching on light soils.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
How do I tell magnesium deficiency from iron or manganese? They all yellow between the veins.
By which leaves. Magnesium is mobile, so it yellows the OLD, lower leaves first and climbs up. Iron and manganese are immobile, so they yellow the NEW, upper leaves first. If the bottom of the plant is affected and the top is still green, it is magnesium.
Can too much potash cause magnesium deficiency?
Yes — this is one of the most common causes. Potassium and magnesium compete for uptake at the root, so heavy, unbalanced potash use can starve the crop of magnesium even when the soil has enough. Easing off the potash and adding magnesium (dolomite or Epsom salt) corrects it.
What is the quickest fix for a standing crop?
A foliar spray of 1–2% magnesium sulphate (Epsom salt) greens up a magnesium-deficient crop within days and is the standard quick fix for fruit trees, grapes and vegetables. For a lasting correction, address the soil with dolomite (acid soils) or soil-applied magnesium sulphate, and rebalance potassium.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.