Garden Planters

Drainage comes first

More container plants are killed by standing water than by drought. An outdoor planter needs a way for water to leave: a drilled base, or a liner arrangement that keeps roots out of what collects. Raising a planter on feet lets water clear and stops the base sitting in a puddle, which also prolongs the planter itself. If you are planting directly into a decorative pot with no hole, use an inner pot you can lift out rather than filling it with compost.

Materials outdoors

Galvanised metal is light, tough and does not mind frost, though it heats up in direct sun and will dry a rootball faster than stone. Stone-effect composites such as fibrestone give the mass and look of stone at a weight you can move, and they are generally frost resistant. Woven finishes suit a softer scheme, and the ones intended for outdoor use are built on a synthetic weave with a plastic lining. Terracotta is handsome and porous, which means it dries quickly and can flake in a hard frost unless it is stated as frost proof.

Weight, moving and where a planter can go

A planter's empty weight tells you very little about the weight you will actually be living with. Compost is heavy and wet compost is heavier, so a large floor-standing planter that two people can carry into position becomes something nobody moves once it is filled. Decide where it goes before you fill it, and plant in place. On a balcony or a roof terrace this stops being an inconvenience and becomes a structural question, so check what the space is rated for and keep the heaviest containers close to the wall rather than the edge. Where a planter has to be moved with the seasons, a lighter composite or metal body, or a plant caddy on castors underneath, saves a great deal of trouble. Fillable and lined planters let you use a lightweight drainage layer in the base rather than filling the whole volume with compost.

Size, scale and grouping

A planter should be bigger than looks necessary. Roots need volume, and a large body of compost dries out far more slowly than a small one, which is the difference between watering twice a week and twice a day in July. Odd-numbered groups of different heights read better than pairs, and repeating one material along a terrace does more for a scheme than mixing several. Check the weight when planted before committing to a balcony or a roof terrace.

Using planters as structure

Planters do a job in a garden that furniture cannot: they divide space without building anything. A pair either side of a door frames it. A run along the edge of a terrace gives a low boundary you can see over and move when you want the floor back. A single large planter with one substantial plant in it settles a corner that looks unfinished. On a hard-surfaced garden with nowhere to dig, containers are the whole planting scheme, so it is worth buying fewer and larger rather than several small ones, which read as clutter and dry out twice as fast.

Watering and winter

Containers dry from the sides as well as the top, so they need water more often than open ground and much more often in wind. Mulching the surface slows it. In winter the risk reverses: a waterlogged planter that freezes can split, and roots sitting in cold water rot. Raise pots off the ground, move tender plants to shelter, and empty anything that cannot drain.

The commonest mistake is watering a little and often, which wets the top few centimetres and leaves the roots below it dry. Water thoroughly, until it runs from the base, then leave it until the surface has dried. Where a planter is going to be hard to reach, or the garden goes unwatered on holiday, a larger container and a mulched surface will forgive far more than a small one. Grouping planters together also helps, because they shade one another and the air between them stays a little more humid than it does around a pot standing on its own in the middle of a terrace. A saucer under a pot helps in summer and hurts in winter, so lift pots off their saucers once the weather turns, so that rain can run away instead of standing under the pot.