Young Leaves Turning Yellow While Old Leaves Stay Green — Iron Deficiency

Iron deficiency has a clear and distinctive pattern that sets it apart from most other nutrient problems: it shows up on the newest, youngest growth first. If the tips of shoots and the freshest leaves are yellow or almost white while the older lower leaves remain green, iron chlorosis is the most likely explanation. This is the opposite of nitrogen or magnesium deficiency, which always appear on older leaves first.

Why New Growth Is Affected First

Iron is not mobile in the plant in the way that nitrogen or magnesium are. Once iron is locked into older leaves it cannot be redistributed to new growing points. So when the supply of available iron runs short, it is the newest growth that suffers. The young leaves lack enough iron to build chlorophyll, so they emerge pale and continue to yellow rather than green up as they mature.

The Soil pH Connection

The vast majority of iron deficiency cases are not caused by a genuine lack of iron in the soil — most soils contain abundant iron. The problem is pH. At pH above 7.0, iron converts into insoluble compounds that roots cannot absorb. The higher the pH, the worse the problem. Acid-loving plants — blueberries, rhododendrons, camellias, azaleas — are most commonly affected, but heavy feeding or liming can push pH high enough to create problems in the vegetable garden too.

Other Causes of Iron Deficiency

Beyond pH, other factors can reduce iron availability:

• Waterlogged or compacted soil, which reduces root function
• Very high phosphorus levels, which can interfere with iron uptake
• Very high calcium or bicarbonate content in soil or tap water
• Cold soil in early spring

How to Treat Iron Deficiency

The most effective short-term treatment is a chelated iron product (also sold as sequestered iron). Chelated iron is formulated to stay available even at higher pH levels. Water it in around the roots according to the product instructions. Results are usually visible within two weeks. Foliar application of chelated iron gives the fastest visible response but needs to be repeated as new growth appears.

For acid-loving plants in alkaline soil, applying acidifying sulfur to lower the pH is a better long-term strategy than repeatedly dosing with iron. Replacing chalky or alkaline tap water with rainwater for container plants can also help significantly.

Long-Term Soil Correction

If soil pH is the underlying cause, lower it gradually using flowers of sulfur or by incorporating acidic organic matter like pine bark, composted bracken or ericaceous compost. A pH in the range 5.5–6.5 keeps iron in its most available form for most plants. Test your soil pH before acting — buying and applying sequestered iron every season is treating the symptom, not the cause.