I bought three today thinking they were a dwarf variety. Wrong! How long do they take to reach full size? I wanted them in a group
Of three but my beds too small for three mature ones.
They reach maximum height by August. As for clump diameter, that will grow over many years but it'll probably increase to 12" over the first 5 years then slow down thereafter.
never have seen a dwarf variety of sedum autumn joy. They are summer bloomers so you'll know by then how tall they will grow to.