In grafted plants are chill hours determined by the sion, the rootstck or both?

In plans to graft several varieties onto one one root stock it raised the question will scion and or root stock effect chill hour requirements? I understand that for effective cross pollination the various grafted scions need to flower about the same time or at lease overlap to insure cross pollination. The question is in grafting does the scion(s) maintain the chill requirements and bloom date or are they effected by the choice of root stock?

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The scion definitely affects, if not determines, the blooming time. When you see blooming date charts for a given species, those are for grafted trees, perhaps to a common rootstock. They don’t tend to call out the rootstock, but do show distinctions across varieties.

As with vigor, I’m sure the actual bloom date is a combination of effect from rootstock and grafted variety.

But if you are talking various varieties on the same stock, the relative bloom sequence is likely to reflect those that have been observed for the respective varieties.

I consider blooming and ripening dates to be relative, not absolute. I try to take into account the climate and growing conditions. It’s more helpful to learn that a persimmon is early or late, or x number of weeks before or after a common variety - than to just read that it “ripens in November” out of context. That may be an early or late ripening cultivar depending on the other factors.

Likewise with bloom dates.


That’s all anyone needs to know. Very well-written.


btw, I have a minium of 6 “plums” on the same Prunus americana’s (native and coming up together is likely) and they all bloom at different times - affected by cultivar . . . There is one that is 3-weeks later than any of the others and I’m talking “full bloom.”

Additionally . . . there isn’t going to be much affect if several rootstock are sourced . . .