Creating a container water garden on a balcony

Start with the space you have

Nothing lifts a balcony or small paved patio quite like water. Even a half barrel's worth brings dragonflies, bees and the sound of movement, and it works in a space no bigger than a doorstep. You do not need a garden or a spade — a sturdy container, the right plants and a small solar pump will do it. Before you buy anything, spend ten minutes studying your site. Note how many hours of summer sun the balcony gets and whether it is sheltered or windswept. Five hours or more will grow dwarf water lilies well; a shadier corner suits iris, marsh marigold and ferns. Rainwater from a diverter is ideal, but on a balcony you will mostly be carrying watering cans, so keep the container within easy reach of a tap.

Choosing a container and getting the weight right

Old oak half barrels, glazed pots, galvanised troughs and even large plastic storage boxes all work, but size matters. Around 60 to 90 litres is the sweet spot — big enough to stay stable in temperature and clear in summer, small enough to move if you ever need to. Aim for at least 30cm of water depth for a dwarf water lily; 45cm is better.

Weight is your real constraint. Water is roughly 1kg per litre, so a 90-litre container with compost, plants and the vessel itself can reach 120kg. Spread that load across wider bearers rather than one small foot, keep it against a wall rather than out on a cantilevered corner, and never balance a pond on a railing. If you rent or live in a block, check your lease or ask the managing agent first — most balconies are fine, but one phone call settles it.

Line a galvanised or metal container with butyl pond liner before filling: zinc and other metals can leach into the water and upset plants. If you use a barrel, check it is genuinely watertight and free of drainage holes.

Planting a small pond properly

Use purpose-made aquatic compost — it is low in nutrients, which is exactly what you want. Ordinary multi-purpose compost leaches phosphate and gives you green soup by July. Plant in baskets lined with hessian, then top the compost with a 2cm layer of grit to stop it clouding the water.

• One dwarf water lily: 'Pygmaea Helvola' or 'Pygmaea Rubra' stay small and flower freely in 30cm of water.
• Two or three marginals: water forget-me-not, lesser spearwort, marsh marigold, blue-eyed grass or a compact iris.
• Oxygenators: hornwort or water starwort, sold loose, simply dropped in to drift.
• A floater or two: frogbit or broad-leaved pondweed for shade and cover.

Skip water hyacinth and water fern: both are banned from sale in the UK as invasive species, and should never be tipped into a ditch or stream. Fill with rainwater where you can. Tap water is fine if you leave it standing in a can for a day or two to let the chlorine dissipate.

Solar pumps and a little movement

A small solar pump transforms a static tub into something alive. A 5-watt panel with a low-voltage pump is plenty for a 90-litre container, and models with a small battery will keep trickling through a cloudy afternoon. Run it as a gentle bubble or a low spitter rather than a fountain that splashes everywhere — you will lose water to the wind and soak the neighbours below.

Keep the pump's intake raised a few centimetres off the bottom on a brick or inverted pot so it does not clog with debris, and lift it out monthly for a rinse. In autumn, when the leaves come down, unclip the pump and store it indoors; frost will crack the impeller housing.

A stone, a ramp and a bee-friendly edge

Even a container pond becomes a small habitat. Bees and wasps come to drink and will drown without somewhere to stand, so leave one or two flat stones just breaking the surface. A piece of rough timber leaning from the water to the rim gives frogs and hedgehogs a way out, and dragonflies will use the upright stems of iris and rush as resting perches.

Avoid goldfish. In a container this size they foul the water, eat the wildlife you are trying to encourage, and struggle when temperatures swing. Let the pond find its own inhabitants — water boatmen, pond snails and the odd visiting damselfly will arrive on their own.

Keeping the water clear through the year

Clarity comes from balance, not chemicals. Aim for roughly half the surface shaded by leaves by midsummer, which starves algae of light and keeps the water cooler. If it turns green in spring, that is usually a temporary bloom while plants are still waking up, and it settles. A small bundle of barley straw in a mesh bag can help, but the real fix is more oxygenators and less sunlight.

• Top up with rainwater in dry spells, keeping the level constant.
• Deadhead lilies and remove yellowing leaves before they rot down.
• Net off fallen leaves in autumn before they sink.
• Thin oxygenators in late spring if they fill the container.
• Overwinter with the container against a sheltered wall, wrapped in bubble wrap or hessian, and never smash ice — rest a ball on the surface or pour warm water over a floating object instead.

After that, the pond asks very little. Ten quiet minutes a week with a pair of scissors and a watering can keeps a balcony water garden looking generous all year — and the wildlife will find it before you have finished your first cup of tea.