Avocado - burying the graft union

[nexxogen]

Hello. This spring I will be grafting some Stewart avocado seedlings with Mexicola and Mexicola Grande scions. My previous attempts to plant seedlings grown from store bought fruits (Guatemalan most likely) in ground have failed as the trees froze to the ground every winter. It is not that cold here, but the cold spells can be prolonged and I don't have any sheltered spots on the property (some cousins have store bought seedlings doing fine in sheltered areas). Now, I know that Stewart is less cold hardy than Mexicola and assuming the seedlings could end up inheriting this trait, I would like to make some precautions to protect the rootstock part.

I have read online that in California, the West Indies rootstocks are being used for their tolerance of many things, but because they are the most cold sensitive type of avocado, the graft union gets buried under ground.

Has anyone had any experience with this burying of the graft union? I know that avocados really don't like being water logged, so this burying kind of sounds like it would increase the chance of the trunk rotting away.

Or maybe someone has other ideas on how to protect the rootstock?

[Finca La Isla]

It’s an interesting concept.  I haven’t buried the graft Union with avocados but I have with other species.  With Mamey sapote I have had a very good experience.  It would be hard to root a cutting of Mamey but the scion started to make its own roots as well.  So, if there was a problem of incompatibility the scion would be able to survive on its own.
Peter

[nexxogen]

So you just buried it below soil level, and not with mulch or something similar?

[Finca La Isla]

Basically yes. The first one I did was a low side veneer graft and I was able to bury it while still in the pot.
I first heard reference to this technique on this forum from a post by Mike T. Then I saw an article about it on an Australian rare fruits page.
Peter

[ScottR]

I have a Duke tree that was grafted onto Mexicola rootstock which I made myself because had scion wood of Duke 7 which is rootstock. So, when I planted in bigger pot I buried the graft union hoping that the Duke scion would send out it's on roots but after 1-year it never did so I planted in ground deep with graft covered with soil but has never re-rooted (Duke scion). I would sure try you have nothing to loose maybe wounding above graft ans applying root hormone might help?
Best of luck and please keep us posted on results!

[nexxogen]

Thanks for the answers guys. The only reason I would want to do this is to protect the rootstock from cold, because it might turn our to be more sensitive than the scion. So it really isn't important for me that the scion also roots. I'm only concerned about the trunk rotting after being planted below soil level. I assume this didn't happen to you? As long as the tree doesn't suffer, I really don't need the scion part to root.

[ScottR]

Heavy mulch around trunk would help protect from hard freezes too!