This post will be a bit of a ramble about the mysterious tree that got me started in backyard grafting, but there are questions for the tree sleuths at the end.
I bought a house 10 years ago with a single apricot tree in the back yard, and a pipeline that means I can’t have anything over the middle of my yard. I moved what I assumed was an apricot volunteer the first year. After recovering from a year of transplant shock and several years of flowers and no fruit I figured out it was actually a plum tree. I figured it probably needed pollinator but did not know what kind of plum it was to pollinate it, so I reached out on facebook and met a friend who is on here who said he’d come graft it with a few varieties to see what took.
The rootstock produces small plums that stay green and taste like green grapes.
We started with a Jam Session, Toka, and Beech. If my research is right Jam is a European, the Toka is an American x Asian and Beech is an American plum.
All three took, with the Jam session being crazy vigorous, giving me fruit in the 2nd year with about 3 feet of growth it’s first year.
In the years since the Toka has also taken off and is filling out nicely, though with poor pollination. I got 1 plum from it last year and this year I might get 5-10.
The Beech grows about 1 inch a year and bloom so late that they never have partner.
After this first initial plum grafting experience I discovered the true source of my volunteer. The lone apricot tree I had started loosing large branches 
and in response started pushing up suckers EVERYWHERE. I’ve had some pop up 33 ft (10m) away! I let some of them grow expecting apricot’s, but it quickly became apparent that these were actually plums. I finally put it together that the apricot was grafted onto a plum rootstock! 
It was with this realization that I decided to work on my grafting technique using all the suckers and that I realized I can do different prunus species on a plum rootstock.
Last year I was able to get a nectarine to graft onto one of the suckers, and this year on my original volunteer I added on a white peach I grew from a pit and cherries (Utah Giant and Vann). I also put on an apricot from the mother tree on to the volunteer. I also have some plums I’ve taken cuttings from around my neighborhood (Empress and some unknown one).
Needless to say I have been impressed with how well this root stock has taken to all prunus varieties I graft on to it. I am assuming that the rootstock is probably a European variety due to how vigorously the jam sessions and Empress plums grew on grafting (over 6ft of growth from a graft last year for a jam session graft !), but then I had an apricot do the same thing, so now I’m not sure.
I am really curious what kind of a plum tree it is, so I’ll post some pictures and some information about it.
It has a light grey bark. The leaves small with a long oval shape. Their color is with very dark green. The leaves are tough/thick with a rough texture compared to any of my other prunes. They pop out around the same time as the flowers, usually early April in northern Utah. The fruit is usually perfectly round, keeps it’s green color and matures to about the size of a quarter to a half dollar. It is a cling stone with a rather sweet flavor, similar to a green table grape. Fruit reaches ripeness in September or late August. In the picture below I have pictures of the leaves in a shot with a peach graft that took on it.
I’ll post more shots of the tree and other grafts below as I think I’m limited to one picture per post.
