MM106 is a bit shorter than Myro. MM106 is about 3-4 meters high while Myrobalan is about 4-5 meters high.

I don't have those rootstocks. I cramped my trees in a small space. I just prune them all open and short (around 10 ft).

I have animal issues (deer, a groundhog, squirrels). So far, it's not too bad. I choose to have short trees and learn to fight the animals instead. I know I could lose.

Relative vigor is much more complex than simply the matter of rootstock- Castleton plum (probably not grown in Australia) or Green Gage are much less vigorous than Valor (sorry, I am not knowledgeable enough about varieties of plums you are likely to grow in Australia to provide a vigorous example you might grow.

When and how much it rains in what type of soil also are equally influential as rootstock and a well drained clay can help create vigorous trees. 106 is a notoriously poor survivor if there is any issue with drainage, by the way, so you probably best make those mounds high. If the clay is poorly drained it will likely have a dwarfing affect once the trees have used up the aerated soil in the mounds.

Finally, pruning will allow you to grow all the trees at pretty much whatever height you want with branch spreading and some summer pruning to help reduce vigor. Also remove excessively vigorous branches more than a third the diameter of the trunk at point of attachment for vigorous varieties. Leave a very short stub if you need a branch in its place.

A normal commercial spacing for 106 would be about 6.5 meters by at least 4 meters around here, so you will need to manage at least some of your trees especially for compactness, IMO.

H-man,

I ordered a Castleton plum from Cummins this year. Originally it would be on Myro but somehow they sent me one with a Marianna GF 8-1 rootstock and said it'll be about 10 ft tall.

I don't mind a shorter tree but have never heard of this rootstock before.

I thought that would be dwarfing but just looked it up and it should be fine. You don't really need to dwarf Castleton unless you are looking for a very tiny tree.

Here is a link that might be useful: geneva rootstocks

Thank you for the link. It's nice to have more info.

Thanks for the info folks. As you can tell, I don't know a whole lot about growing fruit trees!

Harvestman - I did want to go for M111 rootstock for my clay, but there's this massive trend in Australia towards dwarfing everything, and there wasn't anything available on M111 this year. All the suppliers are moving towards smaller and smaller rootstocks.

When you say to make the mounds high, how high are we talking?

Also regarding spacing - the layout I can manage would be symmetrical, sort of like two equilateral triangles, if you can imagine this - the 'base' of each triangle would be running north-south, with e path running between, and with a tree planted at each corner. The distance between the two trees on the north-south axis will be 7 metres, and the width of the path will be 6 metres. The apex of the two triangles would be on the east and west points, and these points are about 4 metres from the other plantings. I thought I could put another tree at each of these east and west points. But perhaps a smaller tree or none at all would be better.