The trees would probably survive, but there will be no growth, and the maturity of the fruit will slow or stop. Low root zone soil temperatures (-55-F) reduce solubility of nutrients in the soil solution, also slows the trees metabolic activity, and reduces nutrient uptake and also the nutrient transport throughout the tree's transpiration stream. Transpiration and nutrient uptake and movement will be again further reduced when air temperatures are also low, or when humidity or precipitation is high as is normal in Seattle. It is not unusual for leaves of citrus trees to be pale or yellow in a cold, wet atmosphere due to an inability to take up sufficient nutrients. If your trees get a large quality of rain, you need to check that the roots retain a good oxygen supply. However, if you trees are in a 5-1-1 medium, this should not be a problem. If you have some of the large older type of Christmas lights, their use could rise the tree's temperature probably in to or near 60-F

There used to be plastic tunnels at the W.S.U. Mt Vernon Experiment Station where overwintering of potted citrus etc. was demonstrated. I don't know what they might have of this nature there now. Maybe look on the W.S.U./U.S.D.A. Cooperative Extension web site to see what they might say about local citrus growing - I don't remember.

After Bob Norton retired from the Station and settled on Vashon he started bringing his potted citrus to be overwintered in the greenhouses of the now closed Colvos nursery. Except for the very few kinds that may be able to persist outdoors for long periods this far north citrus generally are tropical and do not do well below 28 degrees F. Even 10 degrees F. occurs often enough in most of western WA (including Seattle) to make any plants nailed by that comparatively minor level of cold temporary - when I was in the Seattle Rhododendron Society in the 1970s rhododendrons hardy only to double digits were considered tender, completely unsuitable for all but the most maritime sites. Such as where Mike Lee of Colvos once saw a pretty big citrus of some kind in a Bainbridge Island garden that was about two lots distance from the beach. Encounters like this are exceptional rather than recurring because most of this area is too cold for nearly all kinds of citrus plants to become lasting outdoor features.

To avoid problems such as the defoliation you are seeing now with indoor-outdoor potted specimens what you want to avoid is repeated going back and forth between markedly different temperature regimes. So put them out in spring and then back inside in fall, so that they are subjected to only two changes in conditions per year. And move them when the indoor and outdoor temperatures are most alike.

Or keep them inside all of the time, providing a suitably bright and humid situation so that they don't really need to go out. Where they can pick up bugs, that proliferate after the plants come back in.

If I had a yard, I'd definitely have a greenhouse of some kind. Unfortunately that's not an option for me - it's rooftop or inside.

I'd definitely take them inside before a freeze, as mentioned above. As long as it's not a Meyer it shouldn't drop all of its leaves overnight from the sudden change.

The defoliation I'm currently experiencing is from a plant that has been inside continuously since early October, thus why I am considering trying the mostly-outside option.

When I move my trees inside and out due to cold weather I put a plastic bag over them, move them, then in a half hour I remove the bag. It will take about a half hour for the temperature to change.and the sudden temperature change shock to the leaves is avoided.

Hi Pip

The FWG NZL tree you gave me is on a trifoliata hybrid rootstock that some people think is C35. It is doing pretty good right now. I agree Cuban shaddock is JUNK.

Is there any way to tell what my trees might be grafted on to without suckers?

If it is from FWG, NO! They won't tell you. However you can tell with in an inches growth if it is a trifoliate hybrid.

I remember the lemonade having trifoliate.

But I have not noticed any pattern to when fwg uses what rootstock. So to me buying from them has to go along with expecting to graft into something better. If I get a trifoliate then all the better but I won’t assume that’s what’s going to come.

Agreed pip. I really would like to give the Marrakech a go, so even if this one doesn't make it I'll probably order some budwood from the CCPP and graft it to a sour orange from Harris since I don't have a ready supply of sour orange lying around.

Can you just buy a couple sour orange fruits?

One single fruit will give you all the rootstock you’ll need.

But is sour orange going to be a good container rootstock?

PacNorWreck, as you are seeing, different varieties have different hardiness. I would look into the hardiest ones and also be prepared to either bring them in or cover them. Are they in the ground or in pots? Keep in mind citrus roots are much happier and warmer in the ground rather than in pots outside in winter!

Consider for the ground Citrangequat and Kumquat, Meyer lemon.

Unfortunately I don't have any in-ground spots on my property that get enough light, so pots are my only option. I don't have access to trifoliate for grafting, so as far as I can tell sour orange is my best bet. Does anyone have any recommendations for excellent container or indoor rootstock? My assumption was the sour orange was the best I'd have access to.

sour orange, Flying dragon, poncirus trifoliata, and US897 provide about the best fruit quality possible. C35 is OK with kuharske Citrange a bit lower for fruit quality. Rough lemon is in the basement for fruit quality.

I don’t know your age or goals, but buying a tree on good rootstock then cutting the scion off will get you seeds in a couple years.

I have an in ground Seville sour orange tree. The fruit is just now starting to turn orange. In a month or so I will have an unlimited supply of Sour Orange seed if anyone is interested in growing either a tree or root stock.

Hi Silica,

I'd love to take some Sour Orange seed off your hands if you have a good harvest. I also got an email notification about a post from you that looked like it was going to be very informative. It doesn't look like it's in the thread though - did you delete it or did Houzz eat it?

And another tree seems to have bit the dust - Marrakech dropped literally all of its leaves but two today while I was out of the house. I'm going to chop it up and see if I can get anything to root later this week. Limequat on Volk is doing just fine - deep green leaves with no deficiencies; not growing, but blooming off and on and not showing any signs of decline. Rangpur seems to have stopped its decline outside although it's not going to do any growing in deep winter; we got a pretty decent windstorm today too so I'm sure that didn't help - one of the perils of growing outside I suppose.

In my experience the answer is no, citrus will not grow during the Winter at 55 degrees, although they will survive.

You want them to put on any growth, a clear plastic covering may help during Spring and late Fall, will raise the temperature by about 5 degrees during the day.

Warmer temperatures are better than sunlight, where you live. The trees are not going to be able to put on any growth anyway, so might as well overwinter.

(when the tree is just overwintering, 50-60 degrees are fine, since it's in a semi-dormant state and isn't really growing)

It's true citrus in the ground often does better than citrus in pots brought inside during the Winter season but that has more to do with the roots.