I want to start a new multi grafted potted tree from one of the various dwarf varieties that I can find at my local home improvement store.

I really like pigmented oranges so I am thinking of starting with a Moro blood orange tree and grafting the other pigmented oranges onto it as well as everything else that I can get my hands on.

My next preference is a mandarin/tangerine tree. And my third preference is a lemon, probably Improved Meyer lemon tree.

The priority of the varieties that I'd like to graft are pigmented oranges, followed by mandarins/tangerines, lemons, and finally grapefruits.

I know another option would be to start with a bare rootstock. The reason why I'd like to use an existing fruit tree is in case the grafts didn't succeed at least I'd have the original fruit tree to settle for.

If I were to start with a potted dwarf variety at my local home improvement store, which variety would be best suited for what I am trying to do?

Well,
first to answer you question: What is the rootstock tree? Or what is the variety on which you want to put another variety on?

Because it's important to know because of graft compatibility.

Example: You have a lemon tree. You want to graft now to the lemon twigs several other varieties. So it's useless, to know, that the lemon is grafted onto a sour orange rootstock, because you want to graft your variety onto the lemon twig.
If you want to graft a kumquat onto lemon, well, I would have then give the advice, not to do so, because often you have bud take problems, because lemon and kumquat won't match to well.


So, if you have seedling rootstocks trees, like Poncirus trifoliata or any other, that a true rootstock, and it would be no problem, to graft on a large Poncirus tree a mandarin, a grapefruit and a kumquat and establish a huge multi-graft- or so called cocktail tree.

I'm not sure what rootstock Home Depot, or even Lowe's for that matter, uses. I looked on the labels but it doesn't say.

Home Depot, of course, did not grow the trees, they purchased them form a citrus nursery. Did the tree have a tag on them identifiying the grower? If so, you can call the citrus nursery and ask them. The grower is always happy to tell you what understock they used on your trees. - Millet (1,311-)