Why a small pond belongs on a balcony or patio

You do not need a garden to make a genuine difference to British wildlife. A container pond on a balcony, courtyard or patio can support a surprising range of creatures, from damselflies and hoverflies to bees, pond skaters and the occasional frog if you are at ground level. These mini habitats are especially valuable in built-up areas where natural ponds have vanished. The best part? You can run one without touching a mains tap, simply by harvesting rainwater. A sturdy container, a dwarf water lily and a handful of native wetland plants are all you need to begin.

Choosing and siting your container

The container is your pond’s foundation, so choose something robust and watertight. Aim for at least 45cm across and 35–40cm deep, holding 40–60 litres. Anything smaller will overheat quickly and fluctuate in temperature, which stresses plants and wildlife. Frost-proof glazed ceramic, an oak barrel with a butyl liner, zinc or heavy-duty plastic all work well. Avoid terracotta, which cracks in frost and loses water through its porous walls, and thin plastic, which becomes brittle after a season or two.

• No drainage holes. A pond must hold water, so check the base carefully.
• Placement: four to six hours of sun encourages water lilies to flower, but some afternoon shade prevents overheating. Shelter from strong wind, which whips leaves and dries out marginal plants.
• Weight: 50 litres of water weighs 50kg, plus the container and compost. On a balcony, check your load limit and place the pond over a supporting wall or beam if possible.
• Rain access: site it near a downpipe or guttering so you can easily divert rainwater into the pond.

Planting up: dwarf water lilies, creeping Jenny and native companions

Think in layers. A good container pond has oxygenators submerged below the surface, marginals around the edge, and one or two deep-water plants for colour and cover. Dwarf water lilies are perfect for small spaces because their leaves stay compact and their flowers are proportionally small. Try Nymphaea ‘Pygmaea Helvola’ for soft yellow blooms or ‘Froebeli’ for deep red. Plant them in a aquatic basket with aquatic compost, then top the compost with a layer of grit to stop it clouding the water. Position the basket so the crown sits 20–30cm below the surface.

Around the edges, creeping Jenny (Lysimachia nummularia) is a superb choice. This native British plant trails over the rim and into the water, providing cover for emerging insects and softening the hard line of the container. Pair it with other native marginals such as water mint, marsh marigold, lesser spearwort and water forget-me-not. For oxygenators, hornwort and water starwort are reliable and native. Avoid invasive non-natives like parrot’s feather or water hyacinth, which can escape and clog waterways if discarded carelessly.

• Deep water: one dwarf water lily, planted in a basket.
• Marginal: creeping Jenny, water mint, marsh marigold, lesser spearwort.
• Oxygenators: hornwort, water starwort — these keep the water clear and oxygen-rich.
• Compost: specialist aquatic compost, topped with grit. Do not use ordinary garden soil, which is too rich and encourages algae.

Filling and topping up without mains water

Rainwater is the lifeblood of a healthy container pond. It is soft, free of the nutrients that fuel algae, and exactly what native plants evolved with. Fit a rainwater diverter to a downpipe and run it into a water butt, or simply place a clean bucket under a gutter during a shower. Use this to fill the pond initially and to top it up through summer. If you must use tap water in an emergency, let it stand for 24 hours to allow chlorine to dissipate, but do not make a habit of it. Tap water contains phosphates and nitrates that can turn your pond green. Keep the water level stable, especially in hot spells, and never empty and refill the pond completely — you will lose the tiny invertebrates that make it work.

Keeping the pond healthy and wildlife-friendly

Resist the urge to add fish. Even small goldfish eat insect larvae and produce waste that clouds the water. Instead, let wildlife arrive naturally. Add a few stones or a piece of brick that slopes from the water to the rim so that frogs, hedgehogs and beetles can climb out. Leave fallen leaves and dead stems over winter — they provide shelter for overwintering larvae and insects. Blanketweed can appear in spring; twirl it out with a stick, add a small mesh bag of barley straw, and ensure oxygenators and marginals are growing well to outcompete it. Never use chemicals, dyes or algaecides. Mosquitoes may lay eggs, but predators such as pond skaters, damselfly nymphs and beetles usually move in and keep them in check.

A year in the life of a patio pond

In spring, new shoots emerge from the water mint and marsh marigold, and frogs may visit if your pond is at ground level. Summer brings water lily flowers, damselflies patrolling the surface and bees drinking from the margins. By autumn, cut back excessive growth but leave some seed heads and hollow stems for shelter. Oxygenators may sink to the bottom — this is normal. In winter, do not smash any ice that forms. It damages the pond liner and harms wildlife. Simply leave the pond alone and let it rest. By the following spring, you will have a thriving, self-contained oasis that asks for very little and gives back an enormous amount.