Overwintering citrus plants

I have a lemon (Citrus × meyeri, meyer lemon) and two limes (Citrus x latifolia, Persian lime) in pots. The citrus is in a 9 litre pot, the two limes are much younger and in 3 litre pots.

I'm not sure what to do with them over winter? I live in the Midlands in the UK, winters here are very damp, relatively warm (we get frosts but average temperatures are above 0). We don't get much daylight in the Winter.

I have an uninsulated glass greenhouse, it is on slabs and everything in there is damp. I have a shed, wooden structure with a north facing window. I have a centrally heated house with an average temperature of 19 degrees, but only north or east facing windows. I have a 'pantry' room in the house that averages 10 degrees, but is dark (there is a tiny west facing window but it is constantly in shadow).

Best bets for overwintering these citrus plants healthily? I've only had the lemon in the past, and usually I bring it indoors and sit it in a windowsill- it gets too dry, gets spidermite and all the leaves fall off, but it survives to go back out into the greenhouse in spring.

I would go with the greenhouse with just enough heat to keep it above freezing (partition off the part of the greenhouse with the citrus if you don't want to heat the entire greenhouse).  It would allow your citrus to have the most exposure to your limited winter sunlight and the higher humidity would keep the spider mites at bay.  The mostly cooler temperatures in the greenhouse would also keep your citrus in full dormancy.

Some folks will string up Christmas lights in citrus for a little extra heat in the winter.  I have seem them plugged in only for cold spells or on timers (on during the early morning, the coldest time).  One friend strung up lights inside a tent like greenhouse.

I've been collecting notes on growing citrus in a greenhouse, and I seem to see several sources say that Meyer lemon can take several degrees below 0C. So your greenhouse is probably warm enough.

I live in a dry climate with a cold winter, and have used greenhouses a lot for years. If yours is too damp, try cutting back on watering in the winter -- Eliot Coleman says he didn't use to water some of his crops for a couple of months in the winter, but then he found they seemed to stay overfertilised that way and got aphids, so he resumed watering. Also, I mulch all my pots and beds in the greenhouse, and never use a sprayer or sprinkler, only water by pouring water carefully right at the mulch or soil level. I wonder if something like that could help reduce your excess dampness.

Thanks for your ideas. I'd read two main ideas about overwintering citrus- one was to keep them above 10 degrees, and one said that as long as they were above zero they should go dormant and be fine. Given our limited light in winter- dormant seems a better idea.

I don't water in the greenhouse at all in winter- from about September, but it is on slabs so rainwater pools under the greenhouse walls (it is a glass and aluminium greenhouse).

I've put the citrus in the greenhouse, sat on a sheet of polystyrene and raised off the ground (so avoiding the water on the floor and any cold spots). I've draped horticultural fleece over it. When it gets a bit colder I shall rig up a thermostat and something (I've got some old christmas lights, or a heated propagator) to come on if the temperature dips below freezing.

I really hope they survive!

As an update:
As a heat source I sat the plants in a small 22W heated propagator, with a sheet of Styrofoam underneath and to the north side, reflective bubble wrap to the east and west, and horticultural fleece draped over the top, to make a light-permeable overwintering cave.

The chillis haven't done too well in the 'overwintering cave'- it has got too cold for them. The citrus however look great, lots of tiny tiny flower buds very slowly appearing, and no leaf loss! I've kept the temperature above freezing, it has been as low as 0.5C, average of 4C. Too cold for the chilli plants, which have lost all their leaves.

The damp has been a bit of a problem, I've had to clean mould off the citrus leaves- but there's not a lot I can do about that in my climate.

As an update now that spring is well and truly sprung here, the citrus all survived!

No chillis did, the overwintering cave was too cold for them.

I've even got a lemon still on the tree:


Leaves are a bit curled but the plants are growing lots of new leaves now, and flowers that have been slowly growing all winter are now blooming.

We have minus 5 degrees here and citrus survive that. All of them unless the really tropical ones.

It isn't usually the cold that kills them here, we rarely get below freezing- it is the damp! constant rain and humidity and slugs all winter!