Generally late blooming, apple trees need full sun, well-drained soil, and moderate fertility. Can be susceptible to codling moth, apple scab, powdery mildew and gophers. If the variety is not self-fertile, make sure that you have the right pollinizer.
Semi-dwarf trees are on M-111 rootstock (unless stated otherwise) which tolerates wet soil, dry soil & poor soil. It also resists woolly apple aphids and collar rot and is a great all-around rootstock for apples. Semi-dwarf trees will grow to 15'-25', but you can keep them the size you desire with pruning. Trees are 2 years old and should begin to fruit in 4-5 years.
Dwarf apple trees are grafted onto either Geneva 935 or M-27 which are extremely dwarfing rootstocks for apples. M-27 trees are dwarfed to 6-8 ft. and Geneva 935 are dwarfed to 8-10 ft. and are heavier bearing. Both are ideal for high density planting, for small spaces in the garden and are good for container growing.