Planter style matters.

A front door might call for a hanging basket to provide colour and scent at eye level, while a patio offers space for many different planters. If your starting point is a plant, rather than a location, choose your planter accordingly: for example, a hydrangea will require a much larger planter than a geranium. But if your outdoor space is limited, you may want to plant up one large planter, but in a larger location you can combine a number of planters of varying size and shape to achieve a similar effect as a border.
A planter to suit the plant.
A large pot, because it holds more compost is ideal for growing a stimulating combination of plants. Once planted up, however, it will be difficult to move. To lighten the load, fill the base of large pots with polystyrene beads or bits of broken polystyrene plant trays. An additional advantage to using a large planter is that the compost is less likely to freeze around the roots in winter as it might in a smaller pot, also it won't dry out so fast in summer. You need to keep in mind the height of your mature planting when choosing a pot. A dwarf or low-growing plant can look swamped in a heavy planter, whilst a large shrub will look badly proportioned in a narrow pot. Stability is crucial if you are growing a tall plant, which could sway in the wind and eventually topple the pot. Planters with very tapered bases are particularly susceptible. The most stable shapes are regular ones for example square planters, taller planters with wide shoulders, or large, round dishes. To anchor a planter in place, drive a stake into the ground or into the space between two paving slabs, place the drainage hole of the planter over the stake then slip the empty planter over it.
For any successful display you need to consider the form and size of the plants you are choosing, the situation, and the size and shape of the planter. Tall planters suit trailing plants such as ivy, creeping Jenny and ground ivy, which will hang over the planter in soft trails. Such planters ideal for growing lilies or clematis, which both need a deep, cool root run. Shallow planters such as old sinks and alpine dishes are more suited to the delicate forms of rockery plants, spring bulbs such as crocus, and low-growing herbs. Tall and elegant, narrow-necked planters, sometimes called Ali Baba jars, make a curvaceous focus on a patio or if set among plants in your garden. These ornamental pots can look spectacular when full of trailing stems, wispy grasses, or weeping plants, which create a cascade of foliage, like flowing water. However, the narrow necks of these pots make it almost impossible to remove a plant that needs re-potting. Big-bellied planters present the same problem, but both can be used as cachepots, to disguise a plain plastic pot either set in the neck or placed inside the container.