Hi everybody,
I've been reading you all for a few weeks now, and this is my first post in this forum. This topic is specially interesting for me -thank you Simon and rest of members sharing so useful info- since I live in southern Spain, in the coast of Mediterranean Sea and climatic and soil conditions are pretty similar to those of SoCa. In my particular case I do not have trouble with cold since absolute minims here almost never go below 4ºC (39ºF) but I do have the same problems as you with high pH and extremely dry summers. Here it stops raining in June and keeps like this at least until September, but lately I'm noticing that the dry season is getting longer, starting in May the last years.
Regarding rootstocks as you all probably know by other members from my country, the most popular here is Gomera 3, with a good resistance to limestone soils and cold temperatures, and very high resistance to Pseudomonas. Another one with even greater resistance to very high pHs is 13/1 from Israel, available here just in one place as far as I know. This one is a good choice when pH and space are a problem, because is little vigorous.
I found very interesting the advice to let the trees grow until they get the size enough to bear fruit. I gonna have the trouble described in this topic since my 3 mangos are all drafted in the traditional way. One of them, a Sensation, I'm thinking now of removing the scion and let the Gomera 3 of the rootstock grow free. The other two (a Keitt and a NDM 4) I'll probably let them be and see what happens. For the other varieties I wanted to plant (LZ, ST, CC, Maha, PPK) I'm thinking after reading this topic that the most practical way to go could be to look for seeds instead of scions. Seeds should resist better the shipping process and I just would have to select the clon seedling in order to graft it in a Gomera 3 or a 13-1.
Thanks everybody for sharing so useful info!
Jose