How old a rootstock or scion bud can be used for graft?

[EricSC]

I just found that grafting on a fast growing branch or a new branch has a high take-rate than the old branches.   Now the questions are:

1, How old/young a branch can be used as rootstock?  The younger ones may have high take-rate, but also east to be damaged.  How about a 3 month old branch which is firm but still in triangle shape?
2, How old or young a scion bud can be used?  The younger ones have high take-rate, but also are easy to be damaged, such as those on the triangle branch sticks.

[kumin]

There's no real reason young rootstocks or scions cannot be used. However, the mechanics of the physical manipulation of tender, easily dessicated tissues greatly complicates the procedure. You are correct in stating that young tissues are responsive to grafting. The issue, as you recognize is that there's a trade off in the practicality of working with very small, fragile rootstock and/or scions.
I've grafted and budded rootstock at about 1/8" in diameter. It's doable, but tedious and slow. Scions on the other hand need only be firm enough to prevent dessication and crushing by being wrapped too tight. When performing bark flap grafts I prefer slender, flat scions for a neater finished graft.

After using such small diameter stock, it's a relief to work on larger stock.

Small diameter scion on larger rootstock. Bark flap graft. Although not shown, the cambium is exposed on both sides of the scion, which increases cambium contact surface area.

[Millet]

Kumin, great post with much valuable information. Thanks

[EricSC]

Thanks for the valuable detailed explanation.   

I noticed that the young scion buds and sticks are much fast to take and heal with a high success rate.   At the same time, the old ones are slower with lower success rate.