Greetings from just west of Austin:

Last fall, I planted three "cold hardy" avocados in a sheltered location: two Joeys and one Lila (so that I would have both type A and B pollinators). They did well (quickly grew up to about 6' each, and were actually starting to flower.

Then came the Big Chill last February. These "cold hardy" varieties can take temps down to 15-18F, especially if you given them some protection. But despite putting tents over them with light bulbs inside, 8" of snow, 8F lows, and over a week below 20F kicked them in the teeth, and all of them died back to the ground.

Amazingly, both of the Joeys have resprouted just above the graft scar. One is just barely alive (two wimpy sports less than 8" long), but the other has already regrown to about 5' tall and is very healthy.

The Lila resprouted as well, but unfortunately from below the graft scar, meaning it's sprouting from the rootstock and thus is probably is not a cold-hardy variety (which are typically grafted onto warm-weather rootstocks). The new plant is quite healthy (new growth is now about 1.5" thick at the base and about 5' tall), but I suspect it will not like a hard freeze.

Ergo, my question. In the spring, I'd like to graft a type A pollinator (Lila, Fantastic, Opal) onto this clearly healthy rootstock. Anyone have directions or ideas on the best way to graft a scion (which will be much smaller in diameter) onto a larger rootstock?

Ideas welcome.

Wellcome to the forum Ikbonham, Greetings from the other side of the Globe
I love doing Grafting including avocadoes
I believes as long as the cambium layer of both graft and scion are in good contact it will works
it is even better to use an actively growing root stock, one that is still soft like a young stem from seedling (most of the time I graft scion to a seedling root stock, with seed still attached)
But grafting to a large hardwood is also works, if the root stock are too big or the wood is hard, you can insert the scion right between bark and wood, exactly between cambium layer. I wish to do few grafting in near future using this method too
mean while before that, below is my newly result of grafting a variegated scion to a seedling root stock


I remove the sprout of the rootstock

Thanks for the response.

In order to make the resulting plant cold hardy, I'll need to make the graft as close to the ground as possible (if the plant later freezes below the graft, game over for the scion). That means no way the scion and rootstock will be anything close to the same diameter, so some sort of graft as you describe seems to be called for.

So, chip graft? T-window? Cleft graft? Bark graft? Which technique works best for avocados??

BTW, I've read about some folks solving the A/B pollinator issue by just grafting a scion from a Type A variety onto an established Type B (or vice versa). Any thoughts on that (and the best technique for it?)

For a large plant I prefer bark graft approach, since that will give the most contact between cambium. Avocado wood are kind of difficult to heal very well here at my tropical climate, and few centimeter from the cutting surface they easily rotten. We call this type wood soft-wood at my place.
For this kind of "soft-wood" I made a bark peel several inches below the stump surface, this will ensure the graft stay away from the rotten-prone area of the surface.
kind of like this
https://www.houzz.com/discussi...
I made a screen capture from the above link


I think grafting could really help with the problem of pollination as long as you can get them both flowering at the same time. Here at my place, I saw many avocados flowers at different time of the year, quite random, may be because in tropical area there are no distinct season (in terms of light and temperture), so avocados and many trees flowers randomly. However since we have lots of trees within my village, pollination is not a problem. I assume since in your area avocados will mostly flowers simultaneously at spring, so it will be good

Gotcha. Perfect.

Do you seal the top of the stump with wax or somesuch?

I never use wax or covering stuff, since big stump usually have root pressure that keep pumping water to the top, this will create wet area between wax and stump, I am afraid that will induce bacterial or fungal problem. In my case I just cover all the thing including stump and scion in clear plastic bag to keep moisture and to prevent rain water or environmental factor during graft union, excess water will accumulate sometime at the base of the bag, open the bagging if necessary to release water and change with new clean plastic bag. I will open the plastic bag after I can see growth at the tip of the scion, on avocado usually 3 weeks in my climate. I use simple plastic band to bind my grafting, since it is cheap compares to elastic grafting band, The plastic band stays for few weeks more to ensure the graft kept stable
kind of like this post
https://garden.org/thread/view...
But I do see other people use wax or paint the stump with fungicide, I just never done that.