Creating a wildlife-friendly stream bank in your garden

Why the bank is the busiest part of a stream

A stream bank is the junction between water and dry land, and that makes it one of the richest habitats you can create in a garden. It is damp for part of the year, dry for the rest, shaded in places and sunlit in others. That variety is exactly what wildlife needs. Frogs, toads and newts use the water to breed and the bank to feed and shelter. Dragonflies and damselflies climb out of the water on emergent stems to dry their wings. Bumblebees nest in tussocky grass, and birds hunt along the soft edge for insects.

Too many garden water features end with a neat line of rockery stone and close-mown lawn. That looks tidy, but it offers almost nothing. A better bank is softer, messier in places, and planted with things that belong here.

Designing the bank before you dig

Get the shape right and the planting will look after itself. Aim for a slope of about 1:3 or gentler — shallow enough for amphibians to climb out easily and for soil to hold. If your stream runs through a narrow channel, put a shallow planted shelf on at least one side, roughly 30–45cm below the normal water line, so marginals can sit in wet soil rather than in open water.

• Width: allow at least one metre of planted bank on the sunny side. Two metres is better if you have room.
• Levels: build two or three shallow terraces rather than one steep face. Each terrace holds different moisture and suits different plants.
• Soil: use subsoil topped with a thin layer of topsoil. Rich soil grows floppy, lush growth; leaner soil grows tighter, flower-rich plants.
• Liner: a butyl or EPDM liner is easiest, but cover it. Bare liner becomes dangerously hot in sun and gives wildlife nowhere to grip.
• Hide the edge: tuck gravel, pebbles and planted pockets over the liner so the bank looks like a natural transition.

Planting a native mix that works hard

Stick to British natives and you will attract British insects. In the damp zone at the water's edge, try marsh marigold, water mint, ragged robin, cuckooflower and yellow flag iris. Slightly higher up, where the soil stays moist but not waterlogged, meadowsweet, purple loosestrife, soft rush and greater bird's-foot trefoil all earn their place.

On the drier upper bank, sow a wildflower mix with oxeye daisy, knapweed, field scabious, lady's bedstraw and bird's-foot trefoil, plus fine native grasses such as tufted hairgrass and common bent. These grasses form the tussocks that bumblebees and overwintering insects rely on, and they hold the bank together against winter spate.

Avoid invasive non-natives such as Himalayan balsam, floating pennywort and New Zealand pygmyweed. They are illegal to plant in the wild in the UK, and they will smother a small stream within a couple of seasons.

Plant in spring or early autumn, when the soil is warm and damp. Water new plants through their first summer, then let them fend for themselves.

Leave some of it genuinely wild

This is the part most gardeners find hardest. Resist the urge to tidy every square metre. Leave a patch of nettles in a sunny corner — they feed the caterpillars of peacock, small tortoiseshell and comma butterflies. Let a bramble scramble through the hedge line; it provides nectar, blackberries and dense cover for birds and small mammals.

Allow fallen leaves to gather under trees and shrubs instead of sweeping them away. Leaf litter is a nursery for insects, and it feeds the food chain right up to the song thrush. A brash pile of prunings in a quiet corner does the same job, and it costs you nothing but the decision to leave it alone.

Basking spots, refuges and bare ground

Reptiles, amphibians and insects all need somewhere to warm up, and a south-facing bank is perfect. Add a few flat stones or slates laid on bare soil, angled slightly towards the sun. Leave one patch of bank unmulched and unplanted — bare, well-drained earth or fine gravel is a basking surface, and solitary bees will nest in it.

• Leave a few dead stems standing over winter so dragonfly nymphs and other insects can climb out on them in spring.
• Sink a shallow dish of water at bank level, filled with pebbles, so hedgehogs and birds can drink without falling in.
• Stack a small log pile half in shade and half in sun for slow worms and beetles.
• Never use slug pellets or insecticides near the water. Amphibians and dragonfly larvae are the best slug control you will ever have.

Looking after the bank through the year

Manage the bank as a meadow, not a lawn. Cut the wildflower area once a year, in late August or September, and always remove the cuttings — leaving them smothers the plants beneath and feeds the soil so it becomes too rich. Cut half the grass one year and the other half the next, so there is always somewhere for insects to shelter. Leave seed heads on teasels, knapweed and meadowsweet through the winter for the birds.

Check the bank after heavy rain for scour and undercutting, and firm back any eroded soil with a spade. Top up gravel where it has washed away, and pull out any invasive weed before it sets seed.

That is really all the maintenance a good bank needs: a late-summer cut, a bit of repair work, and the discipline to leave the rest alone. Do that, and within a couple of seasons you will have frogs arriving, damselflies drying their wings on your iris stems, and a bank that looks alive rather than merely tidy.