That building and window could work. Noon to dark is probably only about 6-7 hours so you may want to add some supplemental lighting. Youll want to try and keep the roots around 55*f or you could experience leaf drop as the heat from the sun will warm the leaf surface and the roots wont be active enough to cool them down.

Your mix doesnt have to be sandy just needs to drain well. the container forum has a lot of info on well draining soils.

mike

At those temps, under 55 degrees, that is more than enough light and as long as you provide a very porous well draining mix as Mike says, they will just 'idle' without fear of root rot.
No sand of course unless it is very coarse washed sand.
Another benefit is no worries of bugs either at those temps.

Happy growing:-)

Mike

I agree with meyermike, I would not worry about those kinds of temps in a zone 7. Here in zone 6 my sunroom routinely gets into the 40's and even 30's on the coldest nights, citrus, guavas, avocadoes, mango all continue growing. The fact that the temps go back into the 60's or 70's most days from the sun is important. I'm guessing that's your scenario too. You might even consider some thermal mass to help store up heat during the day.

Thank you! The building does stay toasty during the day--it's small and has gas heat.. and I will make sure it stays at 50* or above.. I am really excited..

You will find that they actually excel and thrive in those cooler temps. In warm and dry homes, they really suffer and go into decline. I used to grow citrus in the home--they died. I decided on putting them into a chilly, south-facing garage (covered in glass), in Zone 7 and they thrived!--Just keep them on the arid side in terms of soil moisture.

To tell you the truth, herein lies the truth, it was Njoasis that I took his suggestions to heart.

It worked, and I have been storing my citrus in a very cool room with no heat with no issues ever since. I work feverishly to keep that room no higher than the 50's to low 60's, even if it means keeping a window cracked open on the much warmer days until the sun returns sometime in March.

If I was to bring the temps up, I had better make sure my trees are getting more than 8 hours of direct sun in a sunny south facing window or its bye bye trees.

Mike