If the stem is green, it's still alive and can possibly grow new leaves once the Spring arrives. It looks like you still have a good amount of leaves on your two other trees... which is good. You should look for new growth on your trees, which means they're doing well.

Thank you, I'm concerned since it's so cold outside and the trees are close to the door that I may have cold roots. I've invested in a couple of heat mats, so maybe that will help... I have learned a lot from this site!☺️

What's the temperature of the root ball? If you don't have a fancy soil thermometer a digital kitchen meat thermometer will tell you.

I'm waiting on 2 heat mats because I'm pretty sure that's a problem. I have no idea what to do with them once they arrive. Can you just lay them in the carpet and sit the plants on them? It's been -10 to -20f at times just inches away through my windows. What temperature do you aim for in the soil? Thanks!

Jamie, you will need a temperature regulator to control the temperature of the mat. I have this one but less expensive ones may be available:

https://www.amazon.com/gp/product/B00V4TJR00/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I think the question was about the easiest... My vote would be Calamondin

I agree, of the citrus I've tried, the calamondin and the sour orange were the most forgiving.

I keep my citrus in a south window upstairs, room temp around 60-65F, with no other lights on them; and they do fine. New growth and blossoming now.

Wait, I need to add, the ones that are in a mix more like 511 ( I mix some chopped leaves in also) do well. I've struggled after starting to use straight gritty mix this past summer, and have now lost 2 very young trees so far this winter and am looking at a third that has dropped all the leaves and died back to the trunk. I think that I didn't water them enough, being so used to overwintering my citrus in the other mix for years on a once-a-week watering schedule.

I agree with calamondin and sour orange being forgiving and would like to add navel/cara cara. I have have one of each in my sunroom with many other trees but they are in a more interior location away from the windows with only a grow light and they have not shed one leaf. Both have fruit that are quite large and doing beautifully well. Calamondin trees are so pretty though and very productive. My vote would be for one of those if you can use the fruit.

I vote calamondin too. Of all the citrus I keep indoors during winter, calamondin does best every year.

For the heatmat: 10w/10litre pot is safe to use 24/24, 7/7.

Between the floor and the heatmat you shoud put a stirofoam sheet, in order to heat the pot, not the floor.

Thank you everyone! If my Meyer doesn't make it, a Calamondin is in my future. I usually have a pretty green thumb, but these Citrus are a challenge! Heat mats should be here Monday, so we will see-

I have heard others using 2x2 sheets of drywall as insulation. Available at all big-box home improvement stores.

How is dry wall an insulator? It has an R factor of only 0.45. Styrofoam is much better with an R factor of 5 per inch thickness.

Jamie, have your ever tasted a Calamondin? You should taste one before you purchase a tree.

Do they taste like an orange? Are they bad tasting? I typically like sour fruits for drinks, seafood, fish for seasoning-

Calamondin is used mostly for juicing, and the juice is then mixed into other beverages, much like lime. Flavor is citrusy-bold and extremely tart. Rind is slightly sweet and edible. Seedy. The Phillipines is a major source of processed calamondin (calamansi/kalamansi), but the imported items found locally contain only 6 to 10 % juice. Pure juice is also useful in baking. Local Phillipine-type grocers might carry juice or puree in frozen form.

I don't know how friendly mandarinquat is as a houseplant, the fruits are similar to calamondin but are larger with a thicker, sweeter rind.