Look, you're already stuffing your entire life into a 100 sq ft box, you might as well maximize your balcony's utility as well. With some minor augmentations, you can turn even the tiniest outdoor space into a personal Babylonian Garden.
Plant What in the Where Now?
Before you get started slapping plants up all over the place, you're going to need a solid planting plan. Start with a scale diagram of your outdoor space and try to envision what you'll want to put where, taking into account the plants' lighting, temperature, and moisture requirements as well as any existing furniture, grills, and whatnot. Be sparing in your planning to start—you can always add more plants later—just make sure that you leave enough space for people to move around comfortably out there. Remember, this is your garden, not a nature preserve.
If you're having trouble deciding what to plant, or if your climate will allow for it, head over to Sproutbot. This handy gardening database will not only tell you when to plant, it'll even mail you the proper seeds.
Install a Few Wallflowers
Your patio has plenty of arable space, it's just that it's mostly vertical. To take full advantage of this space, you can always build and install a smaller version of the orchid wall that recently opened at the NY Botanical Gardens. These shallow vertical planters are packed with sphagnum moss or other suitable substrates, seeded with orchids, Bromeliads, ferns, and other aerial-root plants, then hung. They look amazing when done right and properly cared for, but they are labor intensive to construct and maintain.
An easier and less costly option is to use a vertical, soil-based planter. Take the Urban Garden planter for example. These eight planter pouches can be hung on any wall (or off the balcony) and grow more conventional, hardier garden crops rather than temperamental orchids. Just hang it, fill it, and plant it.
If you'd prefer a more compartmentalized approach, or simply don't want a hanger garden taking up the full wall face, you can easily make your own attractive and dirt-cheap alternatives. The Gutter Garden we shared earlier this year has produced roughly 10 pounds of lettuce this season and works well for any shallow-root herbs, decoratives, or crop plants. Plus you can make multiples and stack them at a slight angle up the side of the wall (think the first level of Donkey Kong) then water the top one only and let it run down through the rest. Of you can always just mount some recycled cans to the wall to lend a more rustic feel.
Wall gardens are great—assuming your landlord is cool with you driving anchoring screws into the building's facade. Some added personal green space is not worth losing your deposit over, so if you can't use your walls, exploit your deck's safety railing instead. These planters balance their loads on either side of the railing and provide much-needed root space for their plants. There are a plenthora of options at Home Depot and Walmart, almost all of which are quite inexpensive. Just make sure you measure the width of your railing before you head out to the home improvement center to ensure that whatever you buy will actually fit.
Plant a Living Floor
Who says you can't have a lawn just because your apartment is on the fifth floor? If your terrace is structurally sound and can support the added weight, you can totally grow your own grass lawn no matter how high up you are. Cover the floor with filter fabric, add a shallow layer of gravel under another layer of topsoil, then seed it.
Like vertical orchid gardens, a patio lawn is an awesome conversation starter and focal point for your outdoor space, but it's a major pain in terms of upkeep, requiring regular watering (which also adds a significant amount of weight), fertilizing, and mowing. Seriously, you want to be out there on your knees with hand shears like some schmuck? No, you don't. Just use normal planters instead.
Or, if you're running a bit low on floor space, use nestled, stacked pots instead. Strawberry pots are a prime example, you can install up to a dozen individual plants into a single container, stick it in a well-lit corner, and enjoy fresh fruit throughout the summer. And it's not just strawberries, most anything can be enticed to grow in that manner using the Akro-Mils Stack-A-Pot. These individual planters stack vertically, offset of course, and can accommodate a variety of common houseplants. Plus, clustering post like this slows evaporation and reduces the amount of time you spend watering every day.
On the other hand, if you prefer something akin to ground cover but don't want to try naturalizing your patio floor, take a look at the Fairmount Living Tiles from Shift_Design. These miniature raised beds measure 14 inches square and 4 inches deep. The aluminum outer frame holds a bio-bag filled with soil (like the wall of planter sacks above). Use these as low-lying accent pieces for your taller strawberry pots or other focal items.
Hang a Garden
Your floor and walls look like a scene from the Cambrian era and you've still got plants to install? There's only one place left to go: up. You don't want to overdo it with hanging pots and planters as they tend to get drippy after watering and can visually dominate your patio if the plant it carries becomes overgrown.
Hanging options include the conventional, coconut husk-lined wire basket as well as cuter variations on the theme that would work well for smaller herbs and spaces. You can also hang your stacked planters as well to save valuable floor space but just ensure that whatever overhead beam you're driving the anchor screws into can safely support the weight of whatever you're hanging.