Iron chlorosis
New leaves turn yellow between green veins because alkaline soil locks up iron; acid lovers suffer most.
What you'll see
- The newest leaves turn pale yellow between the veins while the veins stay green.
- In bad cases, leaves turn almost white, get brown edges and stay small, and twigs die back.
- Common on azaleas, rhododendrons, blueberries, gardenias, pin oaks, sweetgum and river birch.
Why it happens
Most soils hold plenty of iron, but in alkaline soil above about pH 7.5 roots can't take it up. Soggy, cold or compacted soil and damaged roots make it worse.
How to fix it
- Test the soil pH before adding anything.
- For quick greening, spray or drench with a chelated iron product as the label says; the effect lasts one season.
- To fix it for good, lower the pH slowly with elemental sulfur, following the label and a soil test, and keep kids and pets off treated soil.
- Mulch with 2 to 4 inches (5 to 10 cm) of compost or leaf mulch, and water less often so the soil drains.
Keep it from coming back
- Grow acid-loving plants only where the soil is acidic, or in pots of ericaceous mix.
- Don't add lime to soil that is already alkaline.
- Keep the soil well drained; waterlogged roots can't take up iron.
Sources
General guidance, not a diagnosis. For valuable, edible or outdoor crops, check with a local extension service or plant expert. Use any product exactly as its label says, and keep children and pets away while it dries.