Why do apples trees have to be grafted?

Actually, they can be grown from seed. You are just not guaranteed to get the same type or quality of apple. On the other hand, you could get a great apple (the apple equivalent of the Hass avocado).

Apples don’t breed true to the parents – i.e., if a Red Delicious flower is fertilized by Red Delicious pollen, the resulting apple seed may or may not grow into a Red Delicious apple tree. It’s unpredictable, and may very easily grow into a tree that doesn’t produce tasty apples.

You could try planting all the seeds, and some of them will – but trees take a long time to grow. So if you want a tree that provides reliably tasty apples, it’s best to use the branches of one that does. The roots will still feed it as if it were its own, if done skillfully.

(All the main varieties of apples you name – everything from MacIntosh to Delicious to Granny Smith – all started out as random apple trees that turned out tasty almost as if by accident.)

I don’t know about apples per se, because I was trained as an agricultural inspector in Florida, where apples are not grown. However, not only do you guarantee the same variety of fruit through grafting, you can also help your trees avoid problems through grafting.

For example, many citrus varieties are grafted onto Rough Lemon root stock because this variety is resistant to nematode problems. Orange varieties are often grafted onto Sour Orange root stock because the roots are particularly hardy so you get more and bigger fruit.

Many agricultural departments in state universities spend a lot of time looking for new varieties with a special flavor or size or color. They then propagate these plants vegetatively – that is by grafting rather than by seed, to keep those beneficial characteristics.

We have apple trees and have worked with Cornell in the past. They will even make trees to match your requirments.
First they match the root stock to best work with your soil and desired size of tree. The root stocks have numbers like M55 or M109 for example. Then they graft the variety you desire: Red delicious. Golden delicious, Double Red Jonathan, etc. You get the best yield and the best apples.
Isn’t science great?

Some interesting apple facts here, here and here.

One of the places I buy my hostas has asked for ‘sports’ of hosta plants; that is, certain parts of the plant, usually leaves, that vary a bit from the parent plant. I have one variegated hosta that has begun producing solid colored leaves, I should get out there and get some cuttings started to see what I can come up with. New plants are being developed all the time, I imagine I could name my new hosta variety Evelyn’s Zebra or some such thing. =)

My trees are about 30 years old. I just checked the Cornell site and found this info on rootstocks . M-9 rootstock is the hot setup now.
Even though my trees put out a tremendous number of apples, they are fossils by today’s standards.

@Lupin, heirloom plants are all the rage right now. Perhaps your apples could fit that description, if they breed true.

@evelyns_pet_zebra We have some full size Red Delicious trees that are 50 years old. They are incredibly high maintenance. They yield tons of sweet, spotted apples that most folks don’t appreciate. Personally I have no trouble just eating the clean half.
The only way I can get decent apples off them is to spray with Captan after every rainfall and I am not willing to do that.
The deer eat very well.

I appreciate your answers, but I still do not know why other fruits like peaches can be grown from seed without using grafts.

@LostInParadise Even Peach trees are grafted. They will grow from seed but not produce the variety you just ate. Why? Most fruit tress are pollenated by either the wind, bees, or other insects. The pollen contains genetic material from other trees and blossoms. The mix is not likely to be the same as the original tree.
Think of it like children. The child has some characteristics of the parents but is never exactly alike. That is a good thing. It means we keep evolving into something better. If we were genetically identical, all it would take is one particular virus to wipe out the species. The reason my red delicious trees get pounded every year is the particular apple scab in my area has had time to specialize. If I plant a new variety it will be clean for a few years but eventually the fungus will figure it out (the ones that don’t, die) and the new trees will be just as spotted as the old.
I suggest you look at a basic biology text or look up genetics. There will be much more info for you there.

I still think there is a particular problem with apples. My only direct experience with this is growing up in the burbs. My father bought what was called a miniature peach tree. It was only about five feet tall, but produced a large amount of small great tasting peaches. We also had an apple tree that was grafted onto another tree.

Actually, @LostInParadise, many varieties of fruit are grafted for a variety of reasons having to do with hardiness, yield, preservation of the fruit type, producing dwarf plants (these are easier to harvest), producing “fruit cocktail” trees (those with several different but related fruits on the same plant), just for fun, to speed up maturity, to make a plant with otherwise desirable characteristics sturdy, and resistance to disease.

As I said above, commercial citrus are all grafted. So are most European-origined grapes. Apples are grafted in part for control of fruit type but also to dwarf the adult tree so apples are easier to harvest. Roses are grafted because many of the most beautiful flowers are on weak plants and grafting makes the plant sturdy.

According to Wikipedia, tomato, cucumber, eggplant and watermelon, eucalyptus, cherries, and many other plants are grafted.

Most fruit trees are grafted including: pears, peaches, persimmons, plum trees. Check this link from University of Georgia.

Micheal Pollan’s The Botany of Desire (which is one of my all-time favorites) has a great chapter about this issue.

Okay, I stand corrected and learned something as well. Thanks all