A very bitter, astringent seedling growing in the historc Pitts orchard north of Cortez, Colorado. It does not take much juice from this apple to improve a cider blend with its tannin.
Choose rootstock type depending on availability:
Malus domestica Standard sized seedling rootstock. This is what trees were historically grafted on. These will be large trees that will grow for a century or more due to their cold hardiness and drought tolerance. Plant 25 feet or more apart.
M111 Semi Dwarf rootstock. 3/4 size of standard. A good compromise if you want a slightly smaller tree. Plant 15 feet or more apart.
M7 Semi Dwarf, Smaller than M111. Probably not as long lived, but produces sooner. Longer lived than M26. Plant 12 feet or more apart.
M26 Dwarf, Short lived (a few decades), fast producing, needs staked, not drought tolerant or as cold hardy, plant as close to 1-2 feet apart.