Brian:

In our zone Granny Smith and Scarlet Sentinel will cross-pollinate; I cannot vouch for the others.

I used to think that the columnar trees were a gimmic, but our Scarlet Sentinel is produces good crops of tasty apples and is very trouble-free. The origin of them is a bit fuzzy, with one nurseryman speculating they came from the Albert Etter collection.

Applenut

I was also led to believe that the columnar's produced relatively poor apples, but at the All About Fruit show this fall I had a yellow one that was much better than average to my taste.

It may have been Golden Sentinel (or perhaps spire was in the name). In any case, it made me rethink columnars.

Good information.

I definitely want to get a few of these trees, but want to ensure that they will be pollinated to even get the fruit off of them!

In anyone's experience - what was the highest yield on these columnars and how long did it take to acheive? I'm guessing that the first year will be pretty small in yield as it grows.

Going by your pruning picture you have a lot more room than you're thinking you'll have. You may not want them because you want the land for something else but you have plenty of room. Put a tapemeasure to your tree's trunk, about 7.5' out in all directions will be that GS footprint.
I'm going to have 1 semi-dwarf cherry, 1 dwarf cherry, 2 espalier apples, 2 dwarf apples and 3 semi-dwarf apples in my approx. 60'x80' backyard that also contains a 35'x30' garden and a 12'x12' shed.

If you actually do have space issues because you want to use your yard for other things or the picture doesn't tell the whole story, you could espalier and they won't take up any more room than your grape vines (in fact a neighbor used to think my apple trees were grapes).

I could potentially put another tree up closer to the house in line with the Granny Smith, but then that would cause the grapes to be shaded in the morning.

That is the trouble I am having is I have to ensure that all of the plants get good sunlight during the day - especially in the morning to help evaporate the morning's dew.

I understand the 7.5' measurement, but if I was to plant another tree, that would be double - 15' - because the next tree would also need 7.5' on all sides as well. This would run right in the way of the grape arbor I have as well. It doesn't help in this picture, but below is the arbor. It is exactly 15' away from the Granny Smith tree, but it is only about two feet in front, not 7.5'. Therefore if another tree grows out, it will begin to entangle with the arbor. This is why putting two of the columnar apples along the side of the arbor would be better suited.

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That is an impressive structure. Did you cement those posts in the ground? You have almost the same house as me (even the color is the same!).

What if you put in dwarf trees? I plant stuff a lot closer then 7.5Ft... a lot closer! Pruning is the key. Might cut down on yield, but i'd rather have a variety in my small yard.

Our sun is pretty much straight overhead in the summer for the North to South. Yes East to West is a problem in wet years. My house shading one of my cherry trees in the morning caused powdery mildew this year.

I was thinking of grapes on a fence, not overhead.

I was going to try and explain espalier but I figured pictures would do better.
The two are dwarfs about 20 years old. Just a standard espalier.
The single is a 15 year old semi-dwarf that is a little overgrown, it started out to be a candelabra shaped espalier but I got sick of doing it once it became ladder work and let it grow naturally. You can see some of the original shape in there. It's 5' away from the fence and hardly bends over it even with the weight of apples, the other direction it does take up its semi-dwarf sized footprint.

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Very nice pictures of the tree. I would prefer to have more natural trees in the yard as it also needs to be appealing since all of the land I have is in the front yard. I have a nature preserve in the backyard that has mature trees that shades the very little piece of land I have back there all day - so I also have to try to stay aesthetically pleasing as well.

For FrankTank's question - I didn't cement the poles in the ground actually. They are about 1.5' down to make the structure about 6.5' tall. Originally the plan was to make it movable in case we move sometime in the future, but I decided that it definitely won't be moved because it would be too hard and make it look bad in the yard with the pavers already down.

I had also thought about doing dwarf trees as well; and I may put a few dwarf pear trees in at some point. But, I think I have decided to go with the columnar and I will put them on the left side of the arbor.

The little boxes in the back of the thing are for the strawberry patches that we'll put in this year as well. So that worked out well because the two columnar apple trees (I found out that Golden Sentinel and North Pole pollinate each other from Rain Tree Nursery) and the tri-star strawberries are all ordered from Rain Tree, and I got a free 25 bunch of strawberries with the order (20% of the order in bonus items if paid for now and shipped in spring).