Oxygenating and Marginal Plants for Garden Ponds

Peltandra or Arrow Arum

A hardy, semi-evergreen perennial from North America, highly regarded for its architectural form and structure. Individual plants aren't particularly large, but a group can be stunning—best suited to larger ponds.

Leaves are bright green, shiny, strongly veined, and distinctly arrow-shaped. Undersides sometimes take on a chestnut hue. In deeper water, they tend to be evergreen.

Tiny greenish flowers on a short spike enclosed by a conspicuous greenish-white spathe appear in early summer, followed by green berries.

Set plants 30cm (12in) apart in spring. Ideal water depth: 0-25cm (0-10in). Choose full sun or very light shade. Plant directly into soil—Peltandra dislikes containers. Remove faded foliage in late autumn. In winter, protect plants not underwater by packing straw or bracken around crowns.

Propagate by dividing creeping rhizomes in spring.

Also found under old names Peltandra undulata or P. sagittifolia. White arrow arum (P. sagittifolia or P. alba) has purer white flowers with red autumn berries. P. virginica often turns evergreen in deep water.

Ranunculus or Spearwort

Most species are relatively invasive—think buttercups in lawns. Ranunculus lingua happily extends creeping roots and colonizes large areas, so not suitable for small ponds. It redeems itself as a marginal with lovely showy flowers.

Blooms are large, ~5cm (2in) across, golden yellow with a sun-glistening sheen. Appear mid-spring to early autumn. Pollinated flowers produce pretty light green mace-like seed heads ripening slowly to light brown.

Long, spear-shaped leaves (hence the name) are bright green most of the season, pinkish when young.

Ranunculus aquatilis is a spreading invasive species with flowers and stems often submerged. Lesser spearwort (R. flammula) is less invasive, lower-growing, and less decorative—suitable for small ponds.

Grow marginal ranunculus in full sun or light shade, plant in spring directly into soil or planting baskets on pond margin ledges.

Remove all old, dying, or dead leaves and stems in autumn to avoid water pollution. Broken stems falling in water often root from leaf nodes—another spread mechanism.

Divide overgrown clumps every 3-4 years in spring.

Propagate by division or sow seeds in moist compost pots in spring, kept in a shaded cold frame.

Sagittaria or Japanese Arrowhead

All sagittarias, from the Far East and northern Europe, are popular and attractive, even considered architectural.

Most common: Sagittaria sagittifolia.
Leaves of Sagittaria sagittifolia (Photo credit: Wikipedia)

Old botanical name S. japonica—still found in nurseries. Leaves distinctive, especially combined with double-form flowers.

Mid- to late summer: fairly large spikes of white flowers with black and red centers. Male flowers at spike tops, females below.

Elegant arrow-shaped leaves held above water; long ribbon-like leaves produced underwater.

S. latifolia similar but less hardy; S. sagittifolia 'Flore Pleno' produces double flowers.

When growing multiple plants, set 23cm (9in) apart. Plant tubers/young plants directly into soil or weigh down and drop at pond edge. Preferred water depth: 5-30cm (2-12in); deeper water = fewer flowers. Cut all growth in autumn. Feed in spring if practicable.

Easiest propagation: divide every 2-3 years when overcrowded, in spring. Also sow seeds under glass in spring.

Edible roots—sometimes called duck potato because ducks in large ponds eat the tubers.

Typha Reed Mace

A tall plant with sword-shaped blue-green leaves reaching considerable heights, framing taller brown-tipped flower stems ('pokers') through summer. Leaves die back in winter but woody flower stems remain, attractive when frosted.

Not for small or lined ponds—has very strong, vigorous pointed roots capable of penetrating most flexible liners! Best for large natural ponds and lakes. Successfully used for riverbank stabilization—massive root systems form a tough, dense, raft-like mat just below surface.

Typha angustifolia (slender reed mace): graceful, slightly shorter, otherwise similar.

T. minima (miniature reed mace): useful for small ponds. Round seed head differs from cigar-shaped heads of others; leaves narrower. Main similarity: tendency to produce pointed roots.

An additional liner layer between root system and pond liner protects the liner, but it's great effort for a plant that's honestly not the most decorative marginal! Cut old foliage in late autumn to prevent water pollution. Typhas don't require feeding.

Propagate: remove root system length with healthy tips/roots, pot in heavy loam or clay soil, place in water.

Veronica Beccabunga or Brooklime

More correctly water speedwell, closely related to familiar blue-flowering wild plant. Common name "brooklime" likely from growing wild in brooks on chalky ground.

Low, scrambling aquatic plant that hides unsightly exposed liners at pond edges. Dark green elliptic leaves borne profusely along branching lighter green stems.

Dainty royal-blue flowers on short branching stalks in late spring/early summer, fading within weeks. Stems reach 2m (6ft)+, blanketing large areas.

Like watercress, brooklime can be a "poor man's water clearance plant"—aerial roots clean excess plant food that would encourage algae.

Genus Veronica has 200+ species; this is the most readily seen aquatic form for sale.
Veronica beccabunga (Photo credit: Wikipedia)

Can become untidy if not trimmed. Pinch out long stem tips to encourage side growth. Fully hardy, leaves remain until late autumn—remove most growth then.

Propagate by planting trimmings in ordinary garden soil, keeping moist for a week or two, then placing in pond.

Zantedeschia aethiopica, Arum Lily or Calla Lily

From South Africa, as well known as a pot plant as for pond fringes. Sometimes called calla lily but shouldn't be confused with Calla palustris.

Quite hardy if crowns protected in winter by straw/bracken mulch—or at least 15cm (6in) of water! Highly variable: impossible to say absolutely if hardy/half-hardy, deciduous/semi-evergreen, or best as marginal/bog plant. In full bloom, a large clump is breathtaking.

Spring/summer: minute flowers on fragrant yellow spikes from center of large white spathe. Large leathery deep green elongated heart-shaped leaves are dramatic.

Varieties: 'Crowborough' taller and hardier; 'Green Goddess' spathes unfurl deep green aging to pale ivory emerald; 'Apple Court Babe' delightful miniature for small pools/contained features, chalk white spathes above bright green leaves.

Grow in full sun or partial shade, damp bog soil or pond edge in water 5-30cm (2-12in) deep. Plant and divide in spring. Flowers produce many seeds, sow following autumn or spring.

Ajuga reptans or Bugle

Hardy spreading plant from northern Europe, available in several color forms from dark greenish-reddish wild type to lighter tricolored cultivars.

Shade-loving, excellent under trees and shrubs if soil stays moist. Irony: leaves not at their best in shade, but plant sulks in sun. No greater mystery than its common name—nobody knows why it's called bugle.

Winter: leaf rosettes close up, larger outer leaves drop, leaving creeping stems (stolons) with plantlets at tips visible. Suitable for growing between paving of informal pond surrounds.

Flowers: short spikes of small lipped purple blossoms in spring.

Cultivars: 'Atropurpurea' (purple flowers, deep purple-bronze leaves); 'Variegata' (deep green leaves, cream margins); 'Burgundy Glow' (claret leaves); 'Alba' (green leaves, whitish flowers); 'Multicolor'/'Rainbow'/'Tricolor' (blue flowers, dark bronze leaves splattered with cream, pink, red).

Easy care: plant autumn or spring, little general fertilizer in spring, water well during dry periods.

Best propagation: division in spring. Individual plantlets planted directly into soil.