One of the big advantages of container gardening is that you have so much ability to adjust the immediate local “climate” your plants are growing in.
If a plant is baking in too much sun, you can pick up the pot and move it to the shade. If it is becoming crowded by an exuberantly growing neighbor, you can slide it over to give both plants more space.
Get creative. If searing sun is a problem, figure out ways to manufacture portable shade. You can use patio furniture to shade a newly transplanted plant, or to help one that is suffering during a heat spell. Cardboard, plywood, or lattice are all inexpensive materials which can be used for creating shade. By using trellises or wires, you can go 3-D and train vining crops like snowpeas, pole beans or small squashes to grow vertically. This frees up space in tight urban conditions, plus you can move more delicate plants into the protected spaces you have created.
Black pots can get hot in baking sun. Shade the rootball by moving the entire plant into filtered shade, or by sheltering it in a cluster with other plants (or simply change to a lighter colored pot).
Cluster your pots into groups. The foliage from shorter plants can shade the pots of larger plants, keeping them cooler and slowing evaporation. You can set a smaller pot onto the soil within a larger pot. Drape trailing foliage down the face of a pot to protect a rootball from the sun’s rays. Don’t get compulsive about cleaning out leaves that catch between the pots in your grouping. The leaves in pockets around the containers may help insulate and retain moisture as well.
If you don’t get much sunlight on your balcony, you may be able to amplify reflected light with panels of mylar (cheap automobile window shades often have it) or white-painted objects (for instance plywood or cardboard). If all else fails, reconsider your plant choices. Leafy greens and green onions can grow lush and tender in low-light or reflected light situations.
excerpt from Food from a Flowerpot by Joanne Poyourow