My trees in ground right now are all mother trees. They are spaced approx 6 feet apart. I plan on keeping them pruned to stay squatty and compact. I keep some in containers (4 containers), but maintaining the 100s of pots in our high desert heat was alot of work. So, I spent 2 weeks putting them in-ground. They even survived our 18 degree F cold snap or ~ -8C cold snap.
The Rosso di Trani, Naples White, Col de Damma Gris, and Brogiotto Bianco now have ~5 inch circumference trunks!