Thank for all inputs. Soursop has lateral roots; so it recoveries from the cold quite well as same as avocado. However, it doesn't like temperature below 40F. In my area, the best time to graft annona family is the beginning of August (after extreme hot weather)
Simon, you did quite a good job on planting fruit trees in containers. The cherimoya rootstock is the seedling of my 8 year seedling. My 8 year seedling provides fruits for 2 years and got killed by December 2013 cold (In addition, I tried to graft different varieties on this seedling. Those grafting weakened it, and it died. )
bsbullie, you are right. The seedling of soursop is more hardy than grafted soursop (I assume you mean soursop on soursop.) I have a seedling soursop. It grows fast from June to November. it is 1 yr old but very bushy and its trunk is about my thumb. My friend bought a grafted soursop from LA and brought back to Fremont. It was about 1-1/2 foot tall. He put it in greenhouse. It never grew taller and later died.
JF, yes, the time of graft and the type of wood are the key of success for grafting the soursop on cherimoya. It is in container without bottom. I planted it between the houses to prevent wind and cold.
Tam, you are right.
Berto, grafting cherimoya on soursop also works. My area has wet cold winter. Root of soursop doesn't like wet cold soil. I can't use soursop as rootstock for Annona family.
Does anybody graft soursop on pawpaw? I have 5 inches pawpaw seedling. I will try when it gets big enough.