Pip, I know nothing about the rootstock, but I did comment to your reply on Mike's thread about which varieties need heat. Check it out...although it is limited experience...

I also did a lot of googling on this after one of the rootstocks grafts i did turned out to be Rich 16 , From what I gathered Rich 16-6 Trifoliate is used a lot in California for Oranges/Mandarins since they handle heavy soils well , they are slight more dwarfing and less vigorous growth than C35 .

Heres some links , text search by Rich 16

http://citrusresearch.org/wp-content/uploads/2007-Michael-L-Roose-Rootstock-Breeding-and-Evaluation.pdf

http://www.crec.ifas.ufl.edu/extension/citrus_rootstock/Rootstock_Literature/Univ.%20CA%20CitrusProdManual%20Rootstock%20Chapter%202014.pdf

Rich 16-6

6b Steve

Before you buy it do you have a place for it. I believe you are frost free up through December. You will also have to pot it in something much more water retentive than 5-1-1. I find here in Cincinnati I need to use a 6-5-1 mix or I will have problems in the summer.

6b Steve

I use crappy potting mix now since the heat and humidity are what they are. I'm not too worried about frost, it's zone 10. If they can't live outside here they can't live outside anywhere in the continental USA.

ive still got 50lbs of 1/8-1/4 turface that I probably won't ever use now.

Pip You still need a mix that is pourus to insure air movement or you tree will have problems. Just use less turface and more compost and peat as I do. I will only have 2 potted tre rs this winter so I will rig each tree with an air suction device so I can use my shop vacuum to push warm air through the trees roots. The dirt will need watering about 1 every 4-6 weeks.

6b Steve