With a little creativity, you'll be surprised how much produce you can farm in the city. First, go vertical. Save precious ground by training vining crops such as peas, pole beans, melons, squash, and cucumbers on vertical supports. Good trellises can be made of lath stakes, bamboo poles, a section of fence, or grow-netting stapled between two upright poles. Go wide with low-growing plants such as leafy crops, onions, and root crops.
Wide-row gardening works on the principle that plants sown closer together in broad bands produce up to 4 times as much harvest as the same area planted single file in separate rows. Individual plants may produce less than when they're spaced according to the seed package guidelines, but, on the whole, the volume produced is greater. Wide-row gardening also reduces weeding, because vegetables grow thickly and choke out weeds. In addition, plants shade the soil, keeping it moist during hot, dry spells.
With double-cropping, you'll get twice the harvest per square foot. To prevent crowding, combine plants with different maturities; for example, sow radishes with slower-growing carrots. When the radishes are ready to harvest, the carrots can take over. Beets planted with broccoli are another good combination. Second-cropping involves planting in succession for constant production. Early-season vegetables, such as lettuce and green onions, leave voids after they're harvested in midsummer. Reseed empty areas with fast-growing crops such as summer squash and bush beans. Later in summer, plant more cool-season crops for a fall harvest.