I have Mandarin Keraji, Satsuma Collot and Flying dragon with grafted Bloomsweet and Duncan Grapefruit.
I have startet 3 winters ago in open ground in z7 with Keraji nd Collot. First winter I protected them with fleece and 80 w heating cable. The last 2 winters Keraji had only passive protection. Collot, due to companian Ichangensis x sinensis together I protected with a heater when temperatures went lower than -7 ° C. The others are now one winter in open ground with passive fleece protection.