How do I overwinter a lemon tree, and why is it dropping its leaves?

Citrus want a cool bright winter, not a warm dark one — which is why the living room kills them, and why leaf drop in January is nearly always a light, temperature or watering problem.

Difficulty: intermediate
Time: 45 min
Read: 5 min

Short answer

Move it under cover before the first frost, into somewhere cool and bright — 5–12°C with as much light as possible. Cut watering right back so the compost is barely moist, stop feeding or switch to a winter citrus feed, and keep it away from radiators and draughts. Sudden leaf drop is almost always a change in temperature, light or watering.

Citrus are not houseplants and they are not fully hardy: they want a Mediterranean winter, which is cool, bright and fairly dry. A warm, dark, centrally heated room gives them the opposite of all three and is why so many lemon trees arrive in October looking magnificent and are bare by February. They are, however, genuinely long-lived and productive in a pot if the winter is right.

What you'll need

A frost-free, cool, bright space — porch, conservatory, cool greenhouse or unheated bright room
Loam-based citrus or John Innes compost
Summer and winter citrus feeds
A moisture meter or a finger (optional)
Fleece for the pot (optional)

Step by step

Bring it in before the first frost, not after.Late September to October in most of the UK. Citrus tolerate a light touch of cold but not frost, and a shock of cold is one of the classic triggers for leaf drop.
Choose cool and bright over warm and dark.The target is roughly 5–12°C with the best light available: a porch, unheated conservatory, cool greenhouse, or a bright unheated spare room. A heated living room is too warm and far too dark for a plant that in nature has full winter sun.
Keep it away from radiators, fires and draughts.Hot dry air and cold blasts from a door are both stressful. A radiator directly beneath a citrus is one of the most common causes of leaf drop in a British house.
Cut watering right back.In winter a citrus uses very little. Water only when the top few centimetres are dry, and let the pot drain freely — never leave it standing in a saucer of water. Overwatering a cool citrus rots the roots, and the symptom is yellowing and leaf drop.
Switch to a winter citrus feed, or stop feeding.Citrus feeds are sold as separate summer and winter formulations for a reason. Use the winter one sparingly from October to March, or stop entirely if the plant is dormant and cold.
Keep humidity reasonable.A conservatory or porch is usually fine. In a dry heated room, standing the pot on a tray of damp gravel, clear of the water, helps a little — misting is largely cosmetic.
Diagnose leaf drop by what changed.Citrus drop leaves in response to change: a move, a temperature swing, over- or underwatering, or a dark position. Work out what altered in the fortnight before it started.
Move it back outside gradually in late spring.After the last frost, usually late May, and over a week or two. Straight from a conservatory into full sun scorches the leaves.
Repot every two or three years, in spring.Into a loam-based citrus compost or John Innes with added grit, one pot size up. Citrus dislike being over-potted, so move up gradually.
Feed properly through the growing season.Summer citrus feed at every watering or as the label directs, from March to September. Citrus in pots are hungry and quickly go yellow without it.

Tips

Yellowing leaves with green veins is usually a nutrient problem, most often iron or magnesium, and a proper citrus feed with trace elements fixes it.
Rainwater is better than hard tap water for citrus, for the same reason as blueberries — lime raises the pH and locks up iron.
Lemons flower and fruit almost continuously, so a tree can carry flowers and fruit at several stages at once. That is normal.
Meyer lemon, calamondin and kumquat are the most tolerant of indoor conditions. A true Eureka or Lisbon lemon wants better light than most houses provide.
A citrus that has dropped all its leaves is often not dead. Scratch the bark: green underneath means it is alive. Correct the conditions and it will usually releaf in spring.

Common mistakes

Overwintering a citrus in a warm living room — Too warm, too dark and too dry all at once. The plant tries to grow in poor light, becomes drawn and weak, and drops its leaves.
Watering on a schedule through winter — A cool citrus uses very little water. Watering weekly out of habit waterlogs it, rots the roots and produces exactly the yellowing and leaf drop people are trying to prevent.
Using ordinary houseplant feed — Citrus need a specific balance and trace elements, and separate summer and winter formulations. General feed produces chlorotic leaves within a season.
Moving it straight outside into full sun in spring — The leaves scorch. Acclimatise it over a week or two in a sheltered spot first.

If it doesn't work

Sudden leaf drop after moving indoors

Cause: Shock from the change in light and temperature — Fix: Settle it in one cool bright place and stop moving it. Reduce watering. Most trees releaf in spring.

Yellow leaves, soggy compost

Cause: Overwatering in winter — Fix: Let the compost dry down substantially, check the drainage, and never leave the pot in standing water.

Yellow leaves with green veins

Cause: Nutrient shortage, often iron or magnesium, made worse by hard water — Fix: Use a proper citrus feed with trace elements and rainwater where possible.

Sticky leaves and black sooty coating

Cause: Scale insect or mealybug, with sooty mould growing on their honeydew — Fix: Wipe or pick the insects off, sponge the leaves clean, and check leaf undersides and stem joints regularly through winter.

Flowers form but fruit drops off

Cause: Erratic watering, temperature swings or a young plant shedding a surplus — Fix: Water consistently, keep the temperature steady, and accept some natural drop.

Questions people ask

What temperature should a lemon tree be kept at over winter?

Cool and bright — roughly 5–12°C. Frost-free but well below normal room temperature, with as much light as you can give it.

Why is my lemon tree dropping all its leaves?

Citrus drop leaves in response to change: a move, a cold draught, a hot radiator, too much or too little water, or too little light. Identify what changed shortly before it started.

Can I keep a citrus in the house all year?

It will survive but rarely thrive. They do far better standing outside from late May to September and overwintering somewhere cool and bright.

My citrus has lost every leaf — is it dead?

Often not. Scratch a small piece of bark; green underneath means it is alive. Put it somewhere cool and bright, water sparingly, and wait for spring.