How Do I Feed and Fertilise a Lemon Tree?

Citrus trees have specific nutritional needs that differ from most other garden plants. They need not only the three main macronutrients — nitrogen, phosphorus, and potassium — but also magnesium and a range of trace elements including iron, manganese, and zinc. Using a general-purpose fertiliser for citrus invariably leads to deficiency symptoms, particularly magnesium deficiency, because general fertilisers do not contain these specialist nutrients in the right proportions. Using a dedicated citrus fertiliser is by far the simplest approach.

When to start and stop feeding

Begin feeding in late February or March as the days lengthen and the tree starts to show signs of new growth. Continue feeding through to the end of September or October. Stop feeding from November through to February — winter feeding of a semi-dormant tree in low light stimulates weak, pale growth that is vulnerable to pests and disease, and the tree has little ability to use the nutrients efficiently.

Frequency and method

For container citrus, a liquid citrus fertiliser applied every two weeks during the growing season is the most responsive approach. Liquid feeds are rapidly available to the roots and can be adjusted quickly if deficiency symptoms appear. Granular slow-release fertilisers are more convenient and can be applied monthly — scratch them into the surface of the compost and water in. Whichever method you use, follow the label rate rather than applying more in the hope of faster results — overfeeding causes salt buildup in the compost that damages roots.

Magnesium supplementation

Even with a specialist citrus fertiliser, container citrus in actively growing years may develop magnesium deficiency, particularly if they are watered frequently (leaching magnesium from the compost) or growing in small pots. A monthly Epsom salts drench (20 g per litre of water applied as a soil drench around the root zone) provides a direct magnesium boost. Alternatively, foliar spraying with Epsom salts solution at the same concentration addresses deficiency faster when interveinal yellowing on older leaves is noticed.

Signs of overfeeding

Overfeeding shows as browning and scorching at the leaf tips and margins — salt build-up in the compost draws water out of the roots rather than into them. If this occurs, flush the compost thoroughly with clean water several times to leach out excess salts, then return to normal feeding at the correct rate. Repotting into fresh compost is the most reliable remedy for severe salt accumulation.