Let  me start at the beginning. I grew up with real, living (I guess really  dying) Christmas trees, trees that you strapped to the roof of your car  and filled the air with pine and dropped needles everywhere and  precariously balanced between the screws in the little red and green  rusted Christmas-tree-holder where you had to keep refilling the water. J  grew up with fake Christmas trees that you store in a bin all year and  pop up willy-nilly at a moment's notice. Each December I make my annual  request to try a real, living tree, and each year J puts his foot down  on this issue. He does not want to deal with the needles, and the sap,  and the (alleged) fire hazard. J is not usually a put-his-foot-down kind  of husband, but he makes it clear that this issue is not up for further  discussion (until next December, in my book). 
So  this is what I came home to one night in early December after work. My  sweet husband had remembered a picture I'd admired online of a Christmas  tree set in a wood stump, and decided to surprise me! He went and  bought a stump and drilled the hole and had the tree set up, lit, and  ready to decorate, with Christmas music playing in the background when I  got home. I absolutely loved it, and we called it our hybrid  (part-real, part-fake) Christmas tree, a wonderful compromise.
Well,  two days after Christmas I looked around at all of the toys and clothes  and gift bags and plastic wrap strewn all over the living room, and  decided CHRISTMAS IS OVER, and it's time to put away this stuff, and as  long as I had this little spurt of energy we better put away the  Christmas decorations too. My mom was a little sad as J and I  energetically took everything down and put it back into storage, but I  just felt relieved to reclaim my living room.
Christmas - Check!
And  then, once all of the ornaments and other seasonal decor was put away, J  took down the tree and moved the stump, and what did we find? A  not-so-merry surprise:

See  that gray stuff? That gray stuff on my grandmother's handmade tree  skirt, one of my most treasured possessions? That gray stuff is MILDEW.
MILDEW.
NOT MERRY.
In fact, I'd say it's a MIL-DON'T. (I can't help it.)
And then, when we lifted up the tree skirt, we saw this:

The  mildew had soaked through the tree skirt into our rug. Our huge, plush,  100% wool rug. Our  giant-splurge-from-Anthropologie-because-after-looking-at-3000+-rugs-online-I-didn't-like-one-half-as-much  rug.
Surprisingly, I did not panic. Probably because J was so  upset. We're like that - one of us can always stay calm and keep the  big-picture perspective when the other is freaking out. 99% of the time  it's J with the steady wisdom, so during the 1% of time it's me I feel  pretty pleased with myself.
I wasn't too worried about the tree  skirt, since I think I can just cut out the center, which already had  rust stains from the aforementioned  red-and-green-rusted-Christmas-tree-holder of my childhood (so really, I  wanted to do that anyway) and then add a little red felt where needed  to turn it into a wrap-around tree skirt.
So I set to work on the  rug with my "natural" disinfectants - Let's try some vinegar! That's  not helping. Let's try some baking soda to absorb it! Hm, maybe I  should've waited until the vinegar dried. Let's try to vacuum the baking  soda up! But now it's some kind of weird paste that won't vacuum up.  Let's look up some mildew remedies online!
J called rug places  and carpet places and all of them said "We don't do that." They didn't  even want us to bring the rug in to look at it. We were like "We will  pay you money to fix our rug!" and they were like "Don't bother. We  don't deal with mildew. We mil-don't." (Okay, they didn't say that last  sentence. But I would have.) Hmmm...not the best sign.
So after  much online research the conclusion we have come to is that we need to  kill the mildew. Sunlight is the best bet. So both the rug and the tree  skirt have been sunbathing in the backyard for...an embarassing number  of days because the rug weighs roughly the amount of two obese elephants  and I can't move it myself, like, can't even move one corner of it, and  I've had a cold the last week and sick, pregnant me has zero energy.  The next step is Borax. Borax is supposed to be some kind of "natural"  cleaner, and apparently, according to the internets, it kills mildew -  we are supposed to sprinkle it on and then vacuum it up a little bit  later. Once we get it out of the yard (and de-grassified from the  attempt I did make at moving it which ended up with it rolled off the  table and chairs J had set it up on into the dead grass in our lawn) we  will Borax it. Everything we've read online says we can't really do  anything about the discoloration (which is dingier and worse than it  looks in the photo), so once we are sure the mildew is dead, we will try  to strategically place the rug to hide the mildew. Worse comes to  worse, we take it to a rug restoration place and hope it doesn't cost an  arm and a leg to cut off a foot of mildew-ed edge of the rug. I  suggested trying to cut it myself and J said absolutely not. Hopefully  our strategic placement plan works.
So that's how our hybrid Christmas tree has kept us in the holiday spirit all the way into January.
J's right - live trees, even hybrids, are trouble. Bah humbug.