Grafting different varieties of avocado? Utuado and Haas

[apullin]

Hi folks,

Can I craft Utuado scions onto Haas rootstock?

I have a nice Utuado tree that I got 3-4 years ago, and it's grown a lot. But it does have some thin lower branches that almost certainly will need to be pruned away.

But I also sprouted tons of seeds from Haas (grocery store avos), and also lots from a random non-commercial variety (Stewart, maybe) growing in my neighborhood.
I did it for fun, but it got out of hand, and I definitely have 20+ trees ranging in size from 2ft-7ft.

As those from seed will almost certainly be useless, I am considering trying to graft them to something known-good.
I suppose I could also take Haas scions from a commercially grafted Haas (or other) tree.

From some searching, people seem to say that all avocados are one species - does that imply they might all be graft-compatible?

[spaugh]

Thry are graft compatible and you can graft whatever you want on them. 

[apullin]

Oh. That's good news.

Follow-up question for anyone: I let some of the sprouted seed avos grow probably too tall/thick. If it's ~15mm wide (4+ feet tall), is that too tall to graft onto? If not, is there a specific height I should cut it back to, and a grafting technique to use in such a case?

(I actually have never grafted before .... if there's anyone in the SF bay area who either wants to show me or wants some cold hardy avo rootstock, let me know ... )