Since it will be inside a lot and in cooler weather, I would suggest the gritty mix. I'm not sure how large their plants are but 12" is probably good to start with but get yourself a nice pot and skip those black nursery pots. I prefer plastic pots with attached watering trays on the bottom but I live in zone 9B with summers that get into 100 degree temps. You will probably need a free draining pot so just plan ahead and buy a cheap tray or something so that water doesn't run everywhere in your house haha. I've never had good luck with clay pots, they look nicer but tend to break quickly for me.

I do well with gritty mix, but if carrying weight is an issue for you 5:1:1 is lighter, and some like the 5:1:1 just as well if not better. I agree with the plastic pots, clay pots tend to be moist/cold in winter for the roots in our zone, even indoors, because it tends to be colder near the windows. I have a tree in a nursery pot that I place inside a pretty ceramic pot, and that's been fine. My 3 yr trees go into 11 or 12" pots.

I actually made the gritty substituting half the granite with perlite to cut weight. I have a bunch leftover from last summer along with plenty of leftover 5:1:1. If gritty is better I will go with that. Mine isn't screened great but that will help in the summer.

Mandarin 1 what else do you grow? Do you get everything to fruit? Any other tips for our climate? Do you use miracid?I have been using osmocote and miracle grow for some other plants. Will that work?

the weight doesn't matter, what is the general consensus on this board of for meyer lemon's 5-1-1 or gritty? Just want to start out on the right foot. I have read tons of posts but can't figure out which one to use (probably means either one will do). If using 5-1-1, should i skip the lime to keep it more acidic?

Queenskitchen, I, too, subbed some perlite in my gritty mix due to weight, it was fine. I think your tree would do well in gritty or 5:1:1, your choice! I also grow variegated pink lemon, key lime, and meiwa kumquat, all have new growth and flowered, and have small fruits right now. I hope to add a Kishu mandrin soon! They're in a West window. For fertilizer I use Foliage Pro at 1/4 tsp per gallon of water, every watering, purchased on line.

I used gritty mix for a few years but unfortunately having the gritty mix directly in heavy ceramic pots is too heavy for me anymore, so soon I'll be changing those trees over to plastic pots with 5:1:1 because of the weight. So you see, I'm not concerned about whether using gritty mix or 5:1:1. The gritty mix worked fairly well (not perfectly) at keeping pots upright in the wind when my trees went outside....that's another consideration. If using 5:1:1 no, definitely don't skip the lime, that volume of bark is quite acidic and the lime "corrects" it.