Leave them outside. I don't bring my trees in hopefully at least a month past first frost. I I usually have my trees outside early march and they come in and go out to weather.Put a bag over your tree when moving it. It will take a half hour for the tree and air to change temperatures. No leaf temp change shock.

Steve

Thanks to you both for the comments; I feel better about leaving them outside now.

For anyone with greenhouse experience, how much cold protection does an unheated greenhouse provide? I'm thinking of either a temporary (Sep-May) setup or potentially year-round, with some black water jugs for temperature moderation and infrared wrap and incandescent Christmas lights for extra heat / insulation. How big a space should I plan on for about 4 containerized trees?

It's possible for citrus trees to survive being left outside in Seattle but usually not a good idea.

Citrus trees in containers have less cold hardiness than trees in the ground because the roots have less insulation, and the smaller rootspace also makes it more difficult for the plant to be able to vigorously recover during the growing season.

Best bet for leaving potted citrus outside would be to place them in a spot sheltered from wind where they will receive plenty of warm sun during the Winter. Typically the citrus that survive will be the slightly more cold hardy varieties like Meyer lemon, Calamondin, or mandarins.

Seattle generally tends to have about a 2-week window of freezing temperatures, so it would be important to protect the trees during that time. (Although there are occasional freezes outside that window)

Reality is you probably won't be able to practicably bring the trees inside during every freeze, but that may be okay (most years) assuming you bring the trees inside during the very depth of continuously cold temperatures (that 2-week window I was talking about), since that's when the temperature will drop the lowest. A quick light freeze or a little frost will not necessarily severely injure citrus.

It's also worth pointing out that it's been an unusual year in this region and hasn't gotten that cold.

When I did the in-out thing during the winter, I dragged the potted tree into an attached garage with low temp about 45-50F. Not into an indoor room.

It tolerated such moves well including one winter, when it sheltered in the garage for a 2-week long stretch while receiving only minimal light from one rather small casement window.

I agree with leaving them outside. In spite of the cold, they will be happier and will get good sun and rain.

I live in an area that gets lows in the high 20s several times in the winter, but most nights are above freezing. I leave my trees outside and never even consider bringing them in. They do just fine. This assumes that you don't have any citrus that are highly frost tolerant like a Buddha's hand.

Thanks everyone. I've left the limequat outside and so far it seems to be shrugging off the change of scenery. I may get a small frost bag for the tree just to shield the leaves from high winds but otherwise it seems to be working well.