Grow a Potted Lemon Tree in a Cold Climate

In Britain a potted lemon tree spends the winter under glass: a frost-free, bright and cool spot
such as a conservatory, a frost-free greenhouse or a glazed porch, with watering cut back but never
stopped. The Royal Horticultural Society is blunt about the alternative: citrus « won’t reliably
survive winters outdoors, even in the warmest parts of the UK ». The harder question is how cool is
cool enough, and here the advice you will find does not agree.

We grow citrus on a farm above Nice, on the French Riviera, where our thermometer has never read
below 1°C since we set up. Our potted trees stay outside all winter, with no fleece and no moving
indoors. That is not a model for a garden in Leeds or Glasgow. It is a reference point, and it lets
us say plainly what overwintering has to give your tree, and where our own experience stops.

Why the recommended temperatures contradict each other

The RHS says some lemons « will be fine as low as 5°C ». Love The Garden, a British gardening
advice site, says lemon trees « ideally need a minimum temperature of 10°C » and
warns that temperatures below 7°C « can severely damage » them. Both are serious sources, and they sit
5°C apart on the same plant.

Part of the gap is the species. The RHS gives a different winter minimum for each citrus: around
5°C for some lemons, 7°C or more for kumquats, above 10°C for limes and grapefruits and
at least 13°C for calamondins. A single figure quoted for « citrus » mixes plants whose winter needs
differ by a factor of two. If your tree is a calamondin sold as a « miniature orange », the cold porch
that suits a lemon will not suit it.

The other part is the room. The RHS explains why citrus rarely make happy houseplants: the main rooms
of centrally heated homes « are usually too warm in winter and the air tends to be too dry ». A low
minimum assumes a cool, bright space; a higher one fits a warmer conservatory. Light, temperature and
humidity have to be set together, not as one number.

What cold actually does to a lemon tree

Love The Garden lists what goes wrong in winter, and the list is telling. Leaf fall: « low
temperatures; draughts, high temperatures in winter; overwatering ». Too cold and too warm both appear,
alongside too wet. A lemon tree in winter is not just fighting frost, it is fighting an imbalance.

On our side of the Channel the picture is the same from a different angle. With a recorded minimum of
1°C, we have never seen a lemon tree freeze on our farm, and we cannot confirm or deny any published
frost threshold. What our readings do show is the other end of the scale: at that level of cool, in
the open, our potted trees come through winter unprotected. That floor also owes something to our
plot, its aspect and its walls; it does not describe the whole Riviera, and it says nothing about an
English winter.

In a pot, the roots pay first

Love The Garden advises always watering with tepid water, because citrus « don’t like cold conditions
and cold shocks to the roots ». A pot gives the roots only a few litres of compost between them and
the cold, so the container deserves as much attention as the tree:

a pot with drainage holes, so that water never has anywhere to sit;
never leave the pot standing in water: the RHS warns this « can cause the roots to rot »;
repot in spring, into a container only slightly larger than the rootball. The RHS cautions that
overpotting into a much bigger pot can cause problems. Autumn is the wrong moment.

Winter watering: not too much, not too little

The RHS is clear about the main risk: overwatering in winter « is one of the commonest problems », so
« err on the dry side ». In winter, let the surface of the compost partially dry out, then water
thoroughly with tepid rainwater and let the excess drain away. Yellowing or shedding leaves can be the
sign of too much water.

We have seen it on our own pots, outdoors and with no hard cold: a winter of too much water showed up
as mould, or as roots that had suffocated. And yet we still water our pots through winter, a little,
even though they also get the rain. Our difficulty with water has never been shortage, it has been
balance. Rather than a schedule, use the RHS test: water when the surface has dried, then nothing
more until it has dried again.

Humidity explains why the same dose behaves differently in winter. The RHS notes that air humidity
sets how fast a plant transpires, and so how much water its roots draw from the compost. In a cool,
humid greenhouse the tree transpires little, and water you would give in July simply stays in the pot.

Measure rather than guess: the min-max thermometer and the hygrometer

Our figures do not come from an impression. We read temperature on a maximum-minimum thermometer and
measure humidity as well. That is how we know our minimum has never gone below 1°C, and that the air
here runs from about 50% humidity by day to 90% at night. It is also the only piece of kit we would
recommend for overwintering, because it answers the three questions the published ranges leave open:

The night-time minimum. Does your conservatory or greenhouse stay frost-free, and above the
floor for your species, at the coldest point of the night? A greenhouse that « never freezes » is
worth checking at dawn after a clear night.
The daytime maximum. A south-facing conservatory can heat up fast in winter sun. Love The Garden
lists high winter temperatures among the causes of leaf fall; if your maximum swings far above your
minimum, the tree gets no settled rest.
Air humidity. This is where the heated house gives itself away. Dry air makes the plant transpire
quickly, and the RHS warns that it can then lose water faster than its roots can absorb it. Love The
Garden suggests standing pots on trays of moist expanded clay to raise humidity indoors.

Leave a min-max thermometer for a week in the place you have in mind. It will tell you whether it
suits before the tree ever moves in.

Bringing it in, taking it out: follow your minimums, not the calendar

The RHS gives the real signal: citrus « must be brought indoors as soon as night temperatures start to
dip in autumn ». Love The Garden suggests outdoor summers mainly from early to mid-June until the end
of August in most of Britain, a window that shrinks or widens with where you live. Your min-max
thermometer, left outside from spring, will tell you when your nights have warmed for good.

If the tree still drops some leaves during winter, do not jump to conclusions: check watering first,
then light, then temperature. Our guide to a
lemon tree losing leaves
works through the causes one by one.

Frequently asked questions

Can a potted lemon tree stay outside over winter in the UK?
The RHS says citrus will not reliably survive winters outdoors, even in the warmest parts of the UK.
On our farm in Nice they do, but our nights have never dropped below 1°C. In Britain, plan on a
frost-free, bright space under glass.

What is the minimum winter temperature for a lemon tree?
The RHS puts it at around 5°C for some lemons; Love The Garden recommends 10°C and warns against
anything below 7°C. Check your species too: calamondins and limes need noticeably more warmth.

How often should I water a lemon tree in winter?
Go by the compost, not the calendar: water when the surface has dried, thoroughly, with tepid water,
and never leave the pot standing in water. Overwatering is the commonest winter mistake; letting the
rootball dry out completely is the opposite one.

Can I keep a lemon tree in the living room over winter?
It is the least suitable option. According to the RHS, the main rooms of centrally heated homes are
usually too warm in winter and their air too dry. A cool, bright conservatory, porch or
orangery
suits it far better.

Sources and further reading

Royal Horticultural Society, Citrus: growing guide:
winter minimums by species, bringing plants in, winter watering and overwatering, humidity, repotting.
Love The Garden, Lemons (Citrus x limon):
minimum winter temperature for lemons, tepid water and cold shocks to the roots, causes of leaf fall,
outdoor season in Britain.

Written and verified by Les Jardins d'un Châtelain, a certified organic farming and fruit-growing business based in Nice, France.