Growing water lilies in a small pond

Why a small pond benefits from water lilies

A water lily earns its place in even the smallest pond. The floating leaves shade the surface, which cools the water and starves blanketweed and green algae of the light they need to multiply. The leaves also give frogs, newts and small fish somewhere to hide from herons and cats, while the flowers bring colour from June right through to September.

The catch is that most water lilies sold in garden centres are far too vigorous for a pond the size of a bath. A vigorous variety can throw leaves across two metres of water and smother everything else. Choose the right one, though, and a modest pond becomes a proper feature with very little effort.

Choosing a lily that fits your pond

Start with the spread, not the flower colour. The label usually gives a spread figure, and that is the area the plant will cover at maturity. As a rough guide, a pond of one square metre wants a lily with a spread of 30–45cm, and anything up to 60cm is workable if you are happy to thin it out every few years.

• Pygmaea group – the smallest reliable hardy lilies. Compact, free-flowering and happy in as little as 15cm of water. Look for Pygmaea Helvola with its soft yellow flowers or Pygmaea Alba in white.
• Small hardy hybrids – slightly larger, with a spread around 45–60cm. Reliable in British winters and better for a pond of two or three square metres.
• Tropical types – vivid blues and purples, but they need warmth, a longer season and lifting before winter. Lovely in a conservatory tank, less sensible in an open UK pond.

Buy bare-root rhizomes in spring if you can. They establish faster than potted plants and you can see exactly what you are getting.

Planting in baskets with heavy loam

Water lilies are greedy rooters and they want soil, not compost. General-purpose potting compost is too light and too rich; it floats out of the basket and feeds the algae rather than the lily. Use a heavy, loam-based soil instead, ideally with a little clay in it. Garden soil from a border works well, provided it has not been treated with weedkiller recently.

Use a large, shallow aquatic basket, roughly 3–5 litres, and line it with hessian if the mesh is wide. Half fill with moist loam, lay the rhizome on top with the growing tip pointing towards the centre of the basket, then cover so the crown sits just at or slightly above soil level. Firm it gently, top-dress with 1–2cm of pea gravel to stop the soil clouding the water and to deter fish from rooting about, then soak the whole basket in a bucket until the bubbles stop.

Lower it into the pond at an angle so trapped air escapes. For small varieties, the top of the basket should sit 15–30cm below the surface; larger ones can go to 45cm. If your pond is deeper, stand the basket on a couple of bricks. Newly planted lilies often prefer shallower water for the first season, so start them high and move them down the following spring.

Position, water and summer feeding

Water lilies want sun — six hours or more of direct light for a decent show of flowers. Shade gives you leaves and little else. They also want still water. A fountain or spout splashing over the leaves will rot them and discourage flowering, so site lilies away from moving water, or run the pump only when you are out in the garden.

Feeding should be modest. Push a slow-release aquatic fertiliser tablet into the soil at the edge of the basket in late spring, and a second one in midsummer if growth looks pale or flowering stalls. That is usually enough for the season. Overfeeding produces soft, sappy leaves and a flush of algae that turns the water green.

Keeping the pond clear and the lily healthy

Little and often is the trick with maintenance. Once a fortnight in summer, cut away yellowing leaves and faded flowers at the base with scissors — leaving them to rot adds nutrients to the water. Check the undersides of leaves for aphids, which cluster on new growth; a jet of water from a hose usually shifts them, and the pond's own insects deal with the rest.

If green water appears, it is almost always excess nutrients plus too much light. More leaf cover from the lily itself will help, along with a few oxygenating plants. Duckweed is a nuisance rather than a threat; skim it with a net before it spreads, and never tip it onto the compost heap where it can wash into drains.

Overwintering and dividing

Hardy lilies need no cosseting. As the leaves die back in autumn, cut them off and let the basket sink to the bottom of the pond, where the water stays above freezing. Tropical lilies must come indoors before the first frost and be kept damp and frost-free.

Every three or four years, lift the basket in early spring and divide the rhizome. Cut it into sections with a clean knife, making sure each piece has a healthy growing point and a few roots, then replant the best piece in fresh loam and pass the rest on. This keeps the lily flowering well and stops it taking over a small pond — which, in a modest water feature, is the one thing you really do need to watch.