Why Is My Lemon Tree Dropping All Its Leaves?

A lemon tree that sheds its leaves in a sudden rush is a dramatic and alarming sight, but it is often a survivable stress response rather than a death sentence. Citrus are evergreen and should hold most of their foliage year-round. When they shed heavily, the tree is reacting to an acute environmental shock. Identifying the shock quickly — and removing it — is the key to recovery.

Cold and Temperature Shock

Moving a lemon from a warm conservatory to an unheated garage, or from indoors to a cold outdoor patio, can cause all the leaves to drop within a week. The cells of citrus leaves cannot cope with the sudden cold and the tree abscises them to reduce water loss from surfaces it can no longer protect. The same happens if a frost catches a tree that was not covered. As long as the woody framework is undamaged — scratch a stem; green cambium means it is alive — the tree will re-leaf from dormant buds when warmth returns. Keep it in a sheltered spot at 8 to 12 °C and water very sparingly until new growth appears.

Overwatering and Waterlogged Roots

Saturated compost starves roots of oxygen and kills them. Dead roots cannot supply water to the canopy, so the tree drops leaves to bring demand into balance with supply. The compost will feel very wet, and the leaves may yellow before falling. Lift the pot and tip it gently to check — water should not pour freely from the base every time you pick it up. Let the compost dry almost completely, then water carefully. If root rot is advanced, repot into fresh, free-draining citrus compost, cutting away any black mushy roots.

Severe Drought Stress

The opposite problem — a completely dried-out root ball — also triggers leaf drop. A pot that has become hydrophobic (bone dry compost that repels water rather than absorbing it) may look as though it has been watered when in fact most of the water runs down the inside of the pot and out the base. Push your finger two centimetres into the compost; if it is completely dry, the tree is thirsty. Stand the pot in a tray of water for twenty minutes to let the root ball rehydrate from below, then drain well. Water more consistently going forward.

Moving the Plant Indoors in Autumn

Many container lemons shed a flush of leaves when moved inside for winter. This is partly a light shock — interior light levels are typically far lower than outdoor light levels even on a dull autumn day — and partly a response to the warmer, drier air of a heated room. Place the tree in the brightest possible position, away from radiators, and mist the foliage regularly to raise humidity. A small fan on low running for a few hours daily improves air circulation and reduces the risk of fungal problems on bare stems.

Pest or Disease Pressure

A severe scale or mealybug infestation, combined with sooty mould blocking light from the leaves, can cause a tree to shed. Root rot fungi such as Phytophthora also cause sudden top-growth decline. If you see pests, treat immediately with an appropriate horticultural oil or systemic insecticide. If root rot is suspected, improve drainage and apply a fungicide drench labelled for Phytophthora to limit further spread.

Will a Bare Tree Recover?

Yes, in most cases. Scratch-test several stems on different parts of the tree. If the wood beneath the bark is green or white and moist, recovery is likely. Keep the tree at a stable moderate temperature (10 to 18 °C), water only when the compost is nearly dry, and wait. The first sign of recovery is small bud swellings at leaf nodes, usually within four to eight weeks of conditions improving. Do not feed until new growth is visibly expanding, as fertiliser on a stressed root system can cause further damage.