Most apple trees need to be cross pollinated ie need pollen from a different variety. Pie cherries are mostly self pollinating, most sweet cherries need a pollinator. Most peaches are self fruitful. Usually pears need to cross pollinate.
Reguarding size Mostly controled by the rootstock of the tree. Go to grandpas grandpa's orchard or cummins nursery and look around they have info on tree size. or google what you want to know.

Very few species of fruit trees are strictly male or female. The only ones that come quickly to my mind are persimmons and the che fruit, but I'm sure there are some others.

Thank you all very much for your responses

When planting apples, pears, or sweet cherries, look around your area. If you have neighbors nearby who have a tree (including flowering crabs for apples), that will provide the pollen for cross pollination of that particular type so you are fine with one tree.

Otherwise consider a multigraft tree so that you have multiple varieties on the same tree if you only have room for 1 of each type of tree.

goo idea. Thanks

Multi grafts are a simple way of planting one tree without the need for more to pollinate. When choosing varieties that need cross pollination make sure they bloom at the same time. Some trees bloom early some mid spring and others later. The rootstock controlls the size of your tree
So ask or check to see if the trees you want come on different rootstocks
I like quince and OHxF 333 as a dwarfing rootstock for our pears
For the most part apples pears and sweet cherries need cross pollination. Bartlet pears are somewhat self fertile.
Meaning in a good year they will bear heavy crops in other years you might get nothing. There are many nurseries out there who could assist you in choosing varieties to work for your situation.
Good luck happy growing
Cory the son of a fruit freak

To me there's an amazing diversity with fruit trees. Some trees either have male flowers or female flowers like persimmon and mulberry. Some trees have some male flowers and some female flowers on the same tree like pecans. And some trees have all the male and female parts on all their flowers (called perfect flowers).

Most traditional fruit trees have perfect flowers, but many of those still require cross pollination, as noted in the posts above, and some can pollenize themselves. It's also interesting to note some varieties have perfect flowers but are pollen sterile, meaning they can produce fruit but require a pollenizer for themselves, but are unable to offer viable pollen to other trees.

On the size issue, most tart cherries, peaches, and to a lesser degree plums are sold on standard rootstocks. On standard roots, tart cherries have about a 15' diameter. In good soil peaches will have a 20' diameter. Plums can also get 20' in diameter.

You should check Walter Reeves website. He's our regional garden person on 750 am in Atlanta. His site links to UGA extension service. My understanding is that cherries and plums are not recommended in Georgia. And the local nurseries like Johnson Brothers in Elijay spell out which ones do the best in the humid south. With the internet you can buy anything, but it doesn't mean it will grow here. And the the home depot and lowes are consistently selling fruit trees that are not recommended for our area. I'll throw in a plug for rabbiteye blueberries (more than one varieity rec),figs(self fertile), muscadine grapes(I don't fully understand) and persimmons(seperate male and female - but I have two female and they are being fertilized by a wild tree somewhere). These plants are indestructable in our area. Apples and pears work, you typically need two different plants and you have to study up on the variety for Georgia because of disease and insect pressure.

"My understanding is that cherries and plums are not recommended in Georgia. And the local nurseries like Johnson Brothers in Elijay spell out which ones do the best in the humid south."

There are several Japanese cross plums developed specifically for the south at the ARS breeding station in Byron GA. The plumcot Spring Satin was also developed there.

Maybe the reference is to European plums?

Olpea, you are right on the european plums. I went back and read what Mr. Reeves has posted and he recommends the Japanese/N.American hybrids. I have to go back to my first recommendation which is to look at Walter Reeves site and/or UGA's extension site.