Why natives make sense at the water's edge

A garden brook is a demanding place to grow. Roots may sit in cold water through winter, then in cracking-dry soil by August. Native marginal plants evolved here, so they cope with that swing without mollycoddling. They also sit comfortably in a British setting — soft greens and muted flowers rather than bold exotics — and they feed and shelter the insects, amphibians and birds that already use your garden.

There is a practical argument too. A dense ribbon of native planting hides the liner edge, the butyl lip or the line of stones where a brook meets the bank. Once it knits together, the join disappears.

Read the edge before you buy anything

Spend twenty minutes with a trowel before ordering plants. Three things matter most.

• How wet, and when. Is the ground permanently saturated, damp for most of the year, or only flooded after heavy rain? Marsh marigold and water mint want the wetter end; ragged robin and meadowsweet cope with merely damp.
• Light. A brook under trees suits sedges and marsh marigold. An open, sunny edge will take water mint, purple loosestrife and flowering rush.
• Depth and flow. Measure the marginal shelf. Most marginals want their crown no more than 5–15cm below the water surface. In a fast-flowing brook, plant in baskets and weight them, or the current will shift them.

Three dependable natives to start with

Sedges (Carex species). The backbone of a natural-looking edge. Carex riparia (greater pond sedge) is vigorous and suits a large brook; Carex pendula (pendulous sedge) has arching tussocks and drooping seedheads, though it self-seeds freely, so deadhead it if you garden on heavy clay. Carex pseudocyperus (hop sedge) is better for smaller gardens, with pale green tussocks and hanging flower spikes. Sedges give cover for froglets and damselfly nymphs leaving the water.

Water mint (Mentha aquatica). Aromatic, quick, and a magnet for bees, hoverflies and small butterflies from July to September. It spreads by runners, so plant it in a basket sunk into the bank if you want it contained — otherwise let it roam and pull out the excess each spring. Lilac-pink whorls of flower sit at the top of stems 30–60cm tall.

Marsh marigold (Caltha palustris). The earliest and cheeriest of the group. Buttery yellow flowers open from March, often before anything else on the edge has stirred, and they are a genuine early-season nectar source. It prefers dappled shade and reliably wet soil, and will sit happily with its crown at or just below the waterline. Leaves die back by midsummer, so pair it with a sedge or water forget-me-not to fill the gap.

Other natives that earn their place

• Water forget-me-not (Myosotis scorpioides) — low, sprawling and long-flowering; perfect for hiding a messy edge.
• Ragged robin (Silene flos-cuculi) — wants damp meadow rather than standing water, and is superb for bumblebees.
• Meadowsweet (Filipendula ulmaria) — taller and frothy, good at the back of a damp bank.
• Lady's smock (Cardamine pratensis) — the food plant of orange-tip caterpillars, so worth a damp patch even if it looks unassuming.
• Yellow flag iris (Iris pseudacorus) — striking, but vigorous and best kept to a contained pond, as it can escape into wild watercourses.

Planting and the first season

Plant in spring or early autumn, when the soil is warm and rain is about. Use aquatic baskets lined with hessian or fine mesh, and fill them with heavy loam or garden soil — not multi-purpose compost, which floats away and feeds algae. Top the soil with 2–3cm of washed gravel to stop birds and fish rooting about. Aim for the crown just level with the surface, and set marginals in groups of three or five for a natural look.

Water in with rainwater from a butt rather than tap water, which is rich in nutrients and encourages blanketweed. In the first year, keep the soil around new plants damp while roots establish. After that, natives generally need no feeding at all — fertiliser in or near water simply grows algae.

Keeping the edge looking good year after year

Leave seedheads and hollow stems standing through winter; they shelter overwintering insects and their seeds feed finches. Tidy sedges and mint in late February or early March, cutting back to about 10cm before new growth shows. Divide congested clumps every two or three years in spring, replanting the livelier outer sections and composting the woody middle. Pull out any thuggish spreader before it takes hold, and watch the bank for erosion where water runs in fast — a few stones and a sedge tussock will usually settle it.

Keep pesticides and lawn fertiliser well away from the edge. A brook is a corridor, and a strip of native planting along it is one of the cheapest, easiest pieces of wildlife gardening you can do.