Years ago I went through a topiary phase, during this phase I decided I would focus strictly on topiaries. At the time I picked up the book The Complete Book of Topiary by Deborah Reich. I believe the book it out of print now but you may come across it in a used book store or at the Chicago Public Library and I highly recommend it. It is a DIY gardening book and has projects that anyone interested in gardening, indoors & outdoors, can do to add whimsy to their plant collection or garden.
In The Complete Book of Topiary there is a section on espalier and it really blew my mind. Espalier is a French word that can refer to the plant being trimmed to grow in a geometrical pattern or to the support system the plant is growing on. Before coming across this horticultural technique-- I'd only ever thought of trees grown in the ground as growing up and over my head, like an umbrella. What blew my mind was seeing trees trained to grow on a two-dimensional plane.
The past couple of years I've been using sunflowers and annual vines to cover the wrought iron fence in front of the house to provide some privacy and protect passersby from being exposed to plumber's crack when I'm playing in the garden. I've noticed a couple of Big Box garden centers carry a few espaliered fruit trees & shrubs and they always end up on clearance for around $10.00, nobody buys them because a lot of people think of fruit trees as growing like I described above.
While visiting Rick Bayless' urban edible garden and the Garfield Park Conservatory I came across several examples of espaliered trees. The photos of the espaliered trees in this post were taken at the Garfield Park Conservatory. They show trees growing against a wall but you could grow them in your yard along a fence to provide privacy and create an urban orchard at the same time. If you want to espalier an apple or a pear, make sure it is growing on dwarf rootstock and that they fruit on spurs--and have a good resistance to diseases and pests. You could go completely ornamental with trees or shrubs like Pyracantha, juniper and witch hazels.
After being inspired by the espaliered trees I saw at Rick Bayless' garden and the espaliers at the Garfield Park Conservatory, I've decided I'm finally going through with my plans of creating my little urban orchard.