Urban gardeners constantly crave space. On a lot less than 1/4 acre in area, with a house, driveway, alder shade (and roots) and a few other things gobbling up arable land, I am always seeking out new ground, including the labor or ripping up a gravel RV driveway. But eventually, short of demolishing the house, there just is no more land. And then it's time to garden vertically.
There are books about small space gardening, but most solutions present themselves. Some plants just obviously want to climb, and it's a matter of the gardener recognizing and facilitating that natural urge. Pole beans want to twine upward (no kidding), hops hop sunward, berry canes arc back to earth only because their exuberant upward growth overshoots ambition and succumbs to gravity. Then there are things like squash and cukes, even tomatoes, that will grow along the ground if nobody helps them out, but which happily accept any support offered.
Gardeners have invented all sorts of ways to get plants to grow upward: trellises and cages, proprietary systems of plant suspension. My preference runs more toward scavenging, buying not much more than a roll of sisal twine. So I cull on hazel coppice to provide some bean poles or make a tipi for the hops to climb. I weave blackberry canes through fence boards, I plant a bean by the scraggly saskatoon. In warmer climes, I grew a small pumpkin (the Seminoles who bred it called it something that translated to hanging pumpkin, and would plant it at the base of dogwood trees that they'd girdled to make a big trellis) that would cover fences and woodpiles, dangling fruit the size of a kid's head.
Hops are the champion climber here. They quickly top the measly 10-foot tripod of branches, and I weave in some withes to extend it. This year, I'm directing the oldest plants into a big hazelnut where they can roam free. We'll see how that works. I planted new ones at the corners of the house, stringing twine up the gables to the peak, which may be a little optimistic in their first year, but then again maybe not.
Raising the foliage means more ground space for little stuff like lettuce that does not have big root systems, matures quickly, and can maybe handle some of the shade that's being created. (Speaking of which, the general rule is that the tallest must be northest, so as not to shade out short stuff unnecessarily--my first round of hops live at the north end of beds.) The second and later sowings may not get so much space, because of that shade and because even the climbers need room for roots, but multi-story gardening still allows me to squeeze a little more food from my limited space.
Pruning proves to be a big part of the game as well. The hops get a leader or two, channeling the strength so the runner has strength and endurance. The Himalayan blackberries would swallow the yard, the house, and slow-moving gardeners if I let it go unchecked, and so I relentlessly rip out the plants I don't want, and cut the thorny medusaic shoots that reach into pathways and other plants' airspace. (And maybe also because sometimes I enjoy the spectacle of a wild thing well kempt--maybe a a counterbalance to my personal grizzleness.) Ultimately, it comes down to productivity, and a high climbing single vine, cane, or runner tends to do that better than an unchecked tangle. Fewer fruits hiding til the rot, more of them growing to their full potential.
Eventually, if I have my way and energy does not fail me, the garden will climb onto the roof. Most green roofs are covered with plants succulent only in the sense that their leaves retain water. I want one that has succulent taste treats. A strawberry patch maybe. The edges will be lined with vines hanging earthward (those tiny Hawaiian tomatoes would work well, now that I think of it), meeting the dirt-rooted plants growing toward the sky. Summers will find my abode knit in a cooling green cloak.
Having drifted from real gardening to flights of fancy, it seems like time to quit. Time to get my hands in the dirt, and off this keyboard.