I’ve grown lots of cacao indoors/outdoors for many years. I haven’t gotten mine to fruit yet, but I did kill many plants, so there’s that. Only 2 years ago, after losing 50 seedlings in the winter, did I battle low humidity indoors, but more on that later.
No idea if it’s better in the attic or outdoors. If it grows nice-looking new leaves, it should be happy. I keep mine outdoors during the summer. Also, cacao doesn’t need or want lots of light, growing well in shade.
I agree you should transplant to a bigger pot-I tend to overpot, but I haven’t had many problems with root rot killing my cacaos, even in very bad potting soil.
Temperature-wise, cacao does best with 60 degrees or more at night (so you’re good for the winter indoors), and up to 90 during the day (though less isn’t always worse-around 80-85 is probably best).
Humidity is very important, during the winter especially. Misting a few times will probably not improve it much. How dry does it get indoors during your winter? Here it’s always below 50 percent, probably closer to 40 or 30. Low humidity is the biggest killer of cacao, and very few plants will survive low humidity. Those that do will be very delicate, and with many years of low humidity will most likely eventually weaken and die. Some of mine are still recovering from low humidity problems, 2 years after I put them in my grow tent.
That is what you’ll have to do, unless you can have a grow room (but that will rot your walls…). My grow tent for the past two years was a pvc constructed, plastic-poly-film covered monster, sitting next to a window and being an eyesore. It wasn’t even that good for the plants, as there was almost no airflow, some plants dried out while others sat in water (and I couldn’t get to them, as I couldn’t fully open the side), and something was off with the sun. But, I misted the inside once a day, and was able to keep a nice high humidity. With the sun shining, the inside got nice and warm and very humid-remember, plants transpire during the day and increase humidity.
Now, I am building a much better grow tent, with a Vivosun tent, circulation fans, grow lights (these black, completely opaque tents need grow lights, and better controls. Hopefully, it will work better.
How tall is your cacao, and how tall do you want to keep it? Cacao naturally branch (the growing tip becomes 3-5 tips growing almost horizontally) at a certain point, usually about 5 feet tall.
Highly recommend you to build a grow tent, without it growing cacao will be a losing battle. With a tent, it will still be troublesome, but at least it will be possible long-term.