At this time, I'm picking State Fair apples, which is one of the early apples that can be grown around here. That got me to thinking that perhaps I can pass on some apple knowledge.
Should you want an apple tree to survive, you must: Select an apple tree correct for this growing zone, support it with posts and ties to keep the wind from shaking the soil loose around the roots, protect it from mice and rabbits by using metal screen around the lower trunk, water it religiously but not too much, and do not let mowers and weed trimmers get close to it. Failure to do these things is the primary reason apple trees fail to make it.
You can also do all those things and -- because you planted it in the shade of some other tree, or in the wrong soil, or it broke due to poor or nonexistent pruning, or you failed to control apple pests, or you let it overbear or bear too soon -- you will still be unhappy with what you have. Apple trees are, it is sad to say, nearly as difficult to raise as children.
But, you say, you grew up with apple trees and no one did those things, to which I reply: Are those trees still alive? Wild apples are one thing. Sweet, edible apples are another. They are good because they are grafted onto special root stock, and that grafting makes them much more to our liking for taste, but much less tolerant of the problems listed above.
Back in the old days, apple trees were planted from seed, and those folks valued apples for cooking, or cider, or for other purposes for which being pretty sour really didn't matter. It turns out that apple trees possess somewhat the genetic variation that humans have. All humans have the same two arms, legs, eyes, ears, etc., but are different. The same thing goes for apple trees. You could plant 10,000 apple seeds and get 10,000 apple trees -- each of which will bear an apple that is somewhat different from other apples. It is a very rare occurrence for one of those 10,000 trees to produce an apple that everyone agrees is tasty.
But once in a great while a perfect apple happens, due to cross pollination (cross breeding, in other words) with another tree. The University of Minnesota, among others, spends years trying to grow the perfect apple by cross breeding one tree's flowers with another tree's pollen, and then growing that apple and planting the seed. It's a process that requires enormous patience. It is also a process that produces countless dead ends before a Honeycrisp or a Fireside or a Honeygold pops up. These are all apples that will not only survive but will produce well here in Zone 4, where winter nights are prone to freeze less hardy trees to death.
Once that perfect tree is grown, then small pieces of limbs -- called scions -- are cut from it, and they are then grafted onto a variety of root stock that is known to be winter hardy. One of the more popular rootstocks comes from Russia, so that gives you some idea of its winter hardiness and sheer vigor. These rootstocks have a great deal in common with crabapples, and in fact the crabapple root itself makes a fair grafting stock. This is why, when the rabbits chew off your tree's bark down around the ground, the root will still poke out new growth, which, if let grow, will turn out to be one of those 10,000 or so apple trees, because it was a crabapple or a cousin of a crabapple.
Feel lucky? Perhaps you could be the proud owner of a wild apple (wild in the genetic sense) that turns out to be the next great apple. More likely, it'll be mainly good for bird food. Even less likely but more likely than the next great apple, it will -- with large amounts of sugar -- be worthy of being baked into a pie.
By sheer serendipity, I have a Red Splendor crabapple tree -- same rules about the 10,000 thing -- that produces a medium-sized apple that is somewhat edible. I'm in the process of attempting to graft this onto another crab rootstock. It is not, however, an apple that many people would pay a nursery $30 for.
By the way, when you buy that nicely branched out apple tree at the nursery and plant it and a couple of years go by and the thing is shooting branches out every which way, and you wonder why?
It's most likely because those limbs that were so nicely laddered on it to begin with were bud grafted onto it. So you would like it.