Iron deficiency

Lime-induced Chlorosis

Iron deficiency, sometimes referred to as lime-induced chlorosis, is a plant disorder that causes the leaves to turn yellow, between the veins, sometimes with brown edges.

1. Leaves turn yellow between the veins, sometimes with brown edges
2. Young leaves may appear bleached

Iron (Fe) is one of the micronutrients or trace elements, needed by plants in relatively small or trace, but essential, amounts. It is important in photosynthesis (the process plants use to harness the sun’s energy to produce sugars and oxygen) and the production of chlorophyll (the light-absorbing plant pigment), so is important for deep green leaf colour.

Iron deficiency is often confused with other problems. Leaf yellowing between the veins can be confused with magnesium or manganese deficiencies, while overall leaf yellowing can be caused by numerous factors – including nitrogen or potassium deficiencies, waterlogging, drought, cold weather, plant virus diseases and even natural leaf drop – including on evergreen plants.

Iron deficiency affects the youngest leaves first, whereas manganese and magnesium deficiencies start with the older leaves. Nitrogen deficiency produces a general yellowing of the whole leaf and in potassium deficiency the yellowing is usually more pronounced at the leaf edges.

Iron deficiency may be caused when there are insufficient suitable iron-containing materials in the growing medium (soil or compost). However, it is more likely when iron is present, but is unavailable for plant roots to absorb it – “locked” in the soil or compost. This is common in alkaline growing media, where the pH is above 7 – which is why acid-loving/lime-hating ericaceous plants, which have a relatively high iron need, are prone when grown in alkaline growing media. It can also be caused when plants are growing in dry soil or compost, which prevents the roots taking up the iron.

Use a simple soil pH testing kit to make sure your soil is acidic – especially when growing lime-hating and ericaceous plants.

• All plants can be affected
• But, in particular, all ericaceous plants (including azalea, camellia, rhododendron and skimmia), citrus (oranges, lemons, limes), pears, raspberries

Keep soil iron levels topped up by feeding with a granular fertiliser that contains iron, especially in spring. Ericaceous and lime-hating plants should be fed with an ericaceous fertiliser. Where soil levels are very low, or plants are showing symptoms of iron deficiency, feed with sulphate of iron.

Liquid feeds will get to work sooner than dry, granular feeds.

Grow plants as well as possible, so they never go short of water. The soil or compost should be kept consistently moist, never allowing it to dry out, without cycles of drying out followed by overwatering.

Make sure soils contain lots of bulky organic matter to hold soil moisture and nutrients. This is particularly important on light, sandy and chalky soils, which contain little organic matter.

Covering the soil with a 5-7.5cm (2-3in) thick mulch will help conserve moisture.

Avoid growing lime-hating and ericaceous plants in multi-purpose and John Innes composts, as these contain lime. Instead, use an ericaceous compost or John Innes Ericaceous Compost.

If you live in an area with chalky/”hard” water, which is alkaline, watering plants, especially container plants, with tap water will gradually increase the pH of the growing medium. To neutralise this, treat with Sulphur Chips every six months – once in spring and once in autumn.

• Fertilisers containing iron
• Ericaceous fertilisers
• Sulphate of iron
• Ericaceous composts
• Sulphur Chips
• Mulches
• Soil pH testing kits