Container grown citrus repotting

That’s a common recommendation when upsizing containers, and you’ll find that recommendation throughout the literature, however I’ve grown several citrus varieties where I upsized directly into 15 gallon nursery containers without any issues. The general concern with a small root ball in a overly large container where the potting soil retains a fair amount water, is the potential for root rot (you don’t have a large root system relative to potting soil volume to uptake that excess water). But if the potting mixture drains well, I’ve personally not found that to be an issue.

Best potting mixture, I can’t say for sure, but I personally mix “garden soil” (composed forest products with some sand added, often called “top soil” in bags at the big box stores) and mix it in a 1:1 ratio (by volume) with peat moss (sphagnum) and appropriate nutrients, etc. It drains well which is important for citrus.

But for 1 plant/pot Miracle Gro makes a “Palm, Cactus & Citrus” potting mix that drains well - I’d probably suggest that. The big box stores usually carry it, but I don’t recall if they carry larger 1 or 2 cubic feet quantity bags.