Once they graduate from a sprouted seed into a real seedling.....maybe even with a few nascent branches :-) Leaf color and shape should at that point be indicative of their future appearance.

How abouf size? Are dwarf maples always grafted?

once you aCHIEVE AN MATURE ROOT MASS.. oops.. then you will start noting annual mature growth rate.. which will then indicate whether a plant is a dwarf.. aka.. annual growth reduced form the species...

keep in mind.. dwarf does not mean it will stay small... it just means annual growth is lower than the norm ... resulting in a smaller plant by the decade...

if tree time is counted in decades.. im guessing you will have your answer if 3 to 5 years.. but in 10 for sure... growing trees is not a hobby for the impatient.. lol ...

ken

" Are dwarf maples always grafted? "

Named forms of ALL Japanese maples are always propagated asexually, primarily by grafting, rarely from cuttings. That is the only way an exact clonal duplicate of that cultivar - true to name - can be produced. Seedling grown JM's regardless of their parentage are just considered as species trees. If you purchase a JM with no graft - or an obvious seedling grown tree - with an assigned cultivar name, you are being hoodwinked! They will ALWAYS be just a straight Acer palmatum - no assigned name can be legally applied.

And contrary to the previous statements, a dwarf JM will stay small - it's in their genetics. Dwarfism is characterized by short internodes, often smaller foliage, dense branching and a tendency to layer or weep - most weeping JM's are dwarf. Graft location can also control mature size. But a dwarf JM that produces seedlings may also produce offspring that will not be fully dwarfed. This can be due to cross pollination with other JM's or with just the wide range of seedling variability. Some will be dwarf; some not.