Oxygenating Plants for the Garden Pond
Eriophorum – Cotton Grass
This is an elegant genus of hardy perennial sedge. Native to high-altitude pools, streams, marshes and moorlands with acid soils, throughout the Northern hemisphere, it is even seen growing in Arctic regions. Suited both to the bog garden and the margins of a pond, it is extremely slow growing, and is quite unmistakeable in summer when its seedheads form cottonwool-like tufts.
Although not the easiest of plants to grow in low-altitude water gardens, it is certainly worth trying. The small insignificant blooms with bright yellow anthers appear in early to mid-spring. They are followed in summer by brown seedpods, which, when they split open they expose attractive tufts of white silky hairs. These are the main feature of the plant, and are most attractive when seen en masse. If the ‘tufts’ are picked when at their best, they dry and last well for floral decoration indoors.
Allow the flower stems to die down naturally each year. The leaves are in shades from olive green to reddish brown, depending on the situation. They are long, slim and drooping, in clumps.
Choose a position in full sun or light shade, in wet peaty acidat the edge of larger ponds, or in shallow water no deeper than 10cm (4in). Plant 23cm (9in) apart directly into wet soil or into baskets. Eriophorum is an undemanding plant, as long as it has acid soil and water. If growing in the bog garden as opposed to growing in water, mulch in spring (particularly if the soil is likely to dry out), and feed with a general fertilizer in spring while young. Keep the plants healthy by dividing the larger clumps every four or five years. If space permits, cotton grass should be planted in bold drifts at the edge of a wildlife pond to create a natural effect.
To propagate, divide larger clumps in spring; either transplant the divisions directly or start them into growth in trays of mud under glass and then plant them out. Alternatively, sow seeds in wet ericaceousunder glass in spring.
The broad-leafed cotton grass (Eriophorum latifolium) is slightly larger and tolerates some lime content in the soil and water but seems to have a shorter life-span.
Houttuynia cordata – Orange peel plant
This is a vigorous and easily grown semi-evergreen plant for the water’s edge or bog garden. It makes attractiveand can become invasive unless confined in some way. ‘Chameleon’ outsells any of the other forms and its brightly coloured leaves never fail to make a talking point. The common name of orange peel plant is due to the citrus-like smell one gets when the foliage, stems or roots are crushed.
In early summer small, white, four-petalled flowers appear on short stalks above the leaves. These flowers are attractive, with heart-shaped green-blue leaves. ‘Chameleon’ (which can also be found wrongly named as ‘Tricolor’ or ‘Variegata’) is a recent man-made hybrid. Here the flowers pale to insignificance when compared to the foliage. The leaves are boldly variegated in shades of pink, yellow, green, cream and white. There are as many gardeners in favour of this plant as there are who would not even think of growing it. Its leaves are, to some, gaudy and unnecessary, while to others they are magnificently ornate. The form ‘Flore Pleno’ has double flowers.
Plant Houttuynia during the spring or autumn, directly into the soil at the edge of the pond, or in baskets to restrain root spread. It prefers a position in partial shade, but will comfortably tolerate either full sun or shade. Planting should be into wet soil or directly into shallow water, no deeper than 10cm (4in). Remove dead or fading foliage and generally tidy up in the autumn. To protect soil-grown plants from frost, mulch with compost in the autumn. Clumps should be divided every four or five years. Divide the spreading roots of larger clumps in spring.
Elodeoides – Marsh St John’s Wort
The hypericum is most familiar as a long-lived shrub; sometimes these are worthy garden plants, and sometimes they are more at home on roadside verges or scrubland. However, this small, creeping species from Western Europe is happiest in mud or water 0-8cm (0-3in) deep. This is the only aquatic hypericum, and may be seen under an often-used incorrect name, Hypericum elodes.
Hypericum elodeoides is a very good plant for concealing the edges of pond liners. Small, yellow trumpet flowers appear at the tips of the stems from mid-summer to early autumn. The leaves are small, oval and woolly, pale green to green-grey.
A sunny spot certainly brings out the best in this plant, but it will also tolerate light to medium shade. Planting can take place in spring or autumn and it is best planted in small groups of three or five, if you have the room. Because it is not large, you may be forgiven for thinking that a small pond is the ideal home for Hypericum, but it is perhaps best used as a small contribution to a massed planting around a medium sized pond, or larger.
Little in the way of cultivation is required. In spring, provide an aquatic fertilizer tablet to help sustain the plant throughout the year, and to inspire it to flower better. In the autumn remove all dead leaves and faded flowers.
To propagate Hypericum, simply divide large clumps in alternate years in spring. Alternatively, you can tryof soft young growth in summer and growing on.
Lobelia Cardinal Flowers
The mainly red-flowering aquatic Lobelias from North America are very closely related to the annual lobelias so beloved of container gardeners for their showy, blue or white overhanging flowers. The aquatic lobelias are different in almost every respect, but mainly they are hardier, taller, and not blue! Although many gardeners are tempted to grow them in ordinary garden soil, they only ever perform at their best with their roots under water.
From mid-summer to early autumn bright, rich red flowers appear in clusters on tall stalks. The glossy, narrow leaves are deepcoloured.
The hybrid of Lobelia cardinalis, ‘Queen Victoria’, is stunning, with carmine flowers and blood-red leaves. Three closely related species are also worthy of mention. Lobelia fulgens is larger and more graceful than L. cardinalis, but is not frost hardy. L. dortmanna is a rosette-forming aquatic species with pale mauve flowers, while L. siphillitica is a very hardy relative with violet-blue flowers.
The best place to plant aquatic lobelias is in full sun or light shade, preferably in water 5-15cm (2-6in) deep, but most will perform well in a moist bog garden. If you live in a colder area, plant them in containers and take them to a frost-free greenhouse for winter. Cut down all top growth in autumn and, if they are growing in a bog garden, cover the crowns with straw or bracken to protect them from the worst of the frosts.
To propagate, sow seeds under glass, or divide plants: both are carried out during spring. Alternatively, take softof the plants during summer.
Mentha aquatica or Water mint
Water mint was once one of the most popular of marginal plants for the average garden. Now, mainly because of brighter and better-hybridized alternatives, this hardy herbaceous perennial is grown mostly in wildlife ponds where it is a good plant for covering the margins with its aromatic leaves and flowers that attract bees and other foragers. It can soon become invasive, however.
Flowers appear from mid to late summer. They are characteristic of most mints: tiny, pale mauve and fragrant, in tight round clusters at the ends of shoots. Prior to flowering, leaf and stem growth can be very rapid, and you may need to control them. Once the flower shoots start to appear, however, this growth slows down.
The small, deciduous, oval, woolly or hairy leaves are dark green turning reddish purple in bright sun. Like all other mints, they are very heavily scented when crushed.
Mentha cervina is less common, but is slightly daintier. It is low-growing and forms leafy clumps with lilac-blue flowers in late summer. Pennyroyal or brook mint (Mentha pulegium) is closely related; dwarf and sprawling, it also thrives in very wet soil.
Plant during spring, in groups of three or four plants maybe, for impact. Choose a position in full sun or light to medium shade. If planted in baskets, these plants will not spread so rapidly and are much easier to keep in check. Cut down all growth in the autumn. Keep the clumps healthy by dividing every other year.
Propagation can be carried out easily in any of three ways: by dividing up clumps, sowing seed in spring, or by taking easy-to-root stem cuttings in the spring or summer.
Menyanthes Trifoliate – Bog bean or Marsh trefoil
The roots of this plant will grow perfectly well in the muddy soil at the sides of the pond, and they will just as happily creep out into deeper water to grow as a true aquatic. In this latter situation, however, the plant tends to be less decorative. It is a low, scrambling plant that will colonize a large area in a few years, so caution needs to be used — do not plant it in a small pond! Bog bean, a native of several Northern European countries, is a rather unsavoury name. To many, the plant is untidy and so not particularly attractive. It is not a true ‘bean’ in the sense that it is not in the same family as the vegetable beans. Its smooth, shiny, bright green, pointed oval leaflets do resemble those of the broad bean, however that is where any similarity ends.
So does it have any redeeming qualities? Its main attribute is that it will cover a pond edge very well, and between mid-spring and early summer lovely white or pale pink star-shaped flowers open. The reddish flower buds are attractive in their own right.
Plant it in full sun or part shade, during mid-to late autumn, or wait until spring. It grows best in a soil that is slightly acid, and a depth of water as much as 25cm (10in) will not harm the plant. Cut down dead stems in autumn.
The aerial rooted stems are ideal for propagation — remove them from the plant, pot them horizontally in a heavy loam, and submerge the pot immediately.
Alternatively, propagate by dividing larger clumps every four or five years. Do this in spring, cutting the creeping rhizomes into several rooted sections. Or you can sow seeds in pots of wet soil during late summer. The only species available is Menyanthes trifoliata.
, Water musk, Yellow musk or Monkey flower
Several musk flowers make excellent plants for pond edges and margins, but they really do need room to grow (being fairly invasive and with their propensity to self-seed), so larger water gardens make the best homes.
Depending on the species and cultivar yellow, orange, red or lavender-blue flowers are carried on tall spikes. Close-up, the blooms have pronounced lips, rather like snapdragons. The leaves are small, rounded, mid-green and deciduous.
The water musk (Mimulus luteus) produces yellow blooms with red blotches during mid-summer. The cardinal flower (M. cardinalis, and not to be confused with the other cardinal flower, Lobelia cardinalis) has attractive downy leaves and bright red, almost scarlet flowers throughout summer. The great purple monkey flower (M. lewisii) carries pink to wine purple coloured flowers from early summer to mid-autumn, and the lavender musk (M. ringens), not surprisingly, carries pale lavender coloured flowers.
The blooms of the monkey musk (M. moschatus) are all-over yellow. In past centuries, this was one of the most richly perfumed garden flowers. Then, inexplicably, around the year 1914, all of the strains of this plant across the world lost much of their fragrance— and have never regained it.
Musks, most of which hail from North America, grow best in full sun in water 0-8cm (0-3in) deep — but 8-15cm (3-6in) deep in the case of M. ringens. Set out young plants, or transplant self-sown, in spring. Cut back dead or dying stems in the autumn.
To propagate, divide overcrowded plants every two or three years; do this in spring. Take softwood cuttings in summer. Seed of some forms, such as M. ringens, can be sown in spring.
Myosotis scorpioides or Water forget-me-not
One of the main attributes of the water forget-me-not is the fact that it emerges from the shallows in spring, at a time when the pond and its immediate environment are still relatively barren. It grows easily in most situations and is very reliable. Its creeping rhizomes are not invasive; they will trail into the water, making this an ideal choice for masking pond edges. It is useful for underplanting irises and other tall.
The flowers are small, rounded, single and of an intense azure blue (with a yellow, pink or white eye). They appear from mid-spring to mid-summer. Deciduous, small, oval, bright green leaves covered in short hairs, are carried on long trailing stems.
There are several varieties worth growing. ‘Pinkie’ is a most attractive form with sugar-pink flowers, and ‘Mermaid’ has large bright blue flowers over a long season. ‘Snowflakes’ is a new hybrid bred in the USA, with lovely white flowers; valuable in the water garden, but it is less robust than the blue forms. A breathtaking effect can be had if this white form is grown among the blue and pink, providing a riot of colour.
Plant in spring or autumn in moist soil close to the water’s edge; a depth of soil 0-15cm (0-6in) is ideal. It will tolerate a position equally well in full sun and heavy shade (some say this plant is the most shade-tolerant of all flowering aquatics). A single plant will spread to 60cm (2ft) in a year; the stems are much longer, but trail down. Cut down dead growth in autumn.
To propagate, transplant the self-sown seedlings (from species only) in spring, or take stem cuttings in summer.