My guess is they just need more time. I can't see the steady warmth being any problem. They have evolved to be slow starting in spring because the new growth is so frost tender.

in conifer grafting.. it has nothing to do with budding.. and in fact you want the buds to remain dormant ..

you tip the tree out of its container.. and look to see if you have active root growth .... fresh white tip growth ...

and that is the key to having an active vascular system.. to allow the callousing.. IF i am using the right terms ... [which i doubt.. lol]

by the time the buds become active.. they will be draining the plant of vital juices ...

is it so much different in fruit???

ken

Mine take about 4 weeks (temp in the low sixties).

Grafting is very different conifers to fruit. Different time, different techniques. Your answer could be very helpful to someone grafting conifers.
John S
PDX OR

gotta learn one new thing a day..

thx for the answer Sky

ken

Thanks, everyone, for sharing your thoughts, and thanks, Dave, for the original idea.

I grafted my first three potted persimmons 3/15 and then another three yesterday. They've about all broken dormancy by now, but I'm letting them go a little longer to make sure the bark is slipping is well (assuming a little more time will help with that.) I've put most of them in an insulated unheated building that's probably been staying in the 40's lately. I've assumed that cooler temperatures like that without extremes would be ideal for the graft unions to heal, but would warmer temperatures actually be better? I could keep them in the house instead. Or I could put them in the back of a cold frame that probably gets up in the 80's during the day and stays at least above freezing at night. If you could control the temperature and humidity and whatever other conditions would affect a graft what would you choose for persimmons?

Persimmon are a warm weather crop. I'd put them in an area more like 70-80F to callus grafts rather than 40s. But this is just my general sense not actual experience with persimmon. To callus grapes and figs I go for about 80F. Persimmon should be similar I'd think.