Using the right vegetation is vital to a balanced natural swimming pool

June 1, 2014

By Markus Winkler and Karen J. Williams

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When planting in natural swimming pools (NSPs), nature should be used as a model, putting together groups of seven, eight or even a dozen of most native species.

Planting in natural swimming pools (NSPs) is not only pleasing, but also plays an important function in the water’s ecological balance. In particular, planting native species is recommended as they are suited to the climate and are generally more robust than non-native specimens. Further, nature should be used as a model, putting together groups of seven, eight or even a dozen of most species. Extremely fast-growing plants should be avoided, if possible, as they have the ability to overpower less vigorous specimens. This article provides a basic guideline for novice NSP designers/builders who should also note the importance of the zone where the NSP is being built. Each zone has its own specific guidelines and rules of thumb which must be adhered to.

First up: Border planting

Outside the NSP’s capillary barrier, pockets of vegetation can be formed using plants that not only work well with the pool, but also fulfil the task of holding back leaves and other debris brought on by wind. Above all, be careful not to create too many biomasses themselves that could land in the water.

Carefully consider which plant life is used. For example, alders and willows would have a negative effect on a NSP, whereas grasses, large-leaved flowering plants, iris, and evergreen shrubs are especially suitable. When it rains, however, no mulch or humus from the plant beds should float into the pond; the capillary barrier should always be higher than the plant beds.

Shore planting using hardy marginals

When planting in the shore area—approximately 305 mm (12 in.) deep—make sure the colours co-ordinate and the species do not fight/compete amongst one another. The swamp and shore plants always bear a changing water level; if the water level lowers, the roots grow towards it, and the shore zone remains damp by capillary action. Short-term overflows are also borne well. The thicker the shore plants are, the less substrate is washed out by rain.

Hardy marginals are the largest grouping of pond plants and are also the most diverse. They are categorized as such because their roots grow under or within an unfettered supply of water and their shoots/foliage can be found either floating or growing upright above the waterline. Highly adaptive and tolerant, hardy marginals are the ultimate survivors, thriving in a range of conditions from completely submerged to intermittent watering.

Each plant has a specific ‘hardiness zone,’ as well as a preferred moisture level in which it grows best. The sheer amount of shapes, sizes, and colour mean hardy marginals have their place in every pond and, thus, have the ability to design and shape the pond landscape like no other group of plants. The following are some examples:

Variegated sweet flag (Acorus calamus)

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Variegated sweet flag

Zones: Four to 10.

Exposure: Full sun to part shade.

Height: Up to 1524 mm (60 in.).

Planting depth: Moist soil and will tolerate standing water in the spring and summer months. Among northern native Americans, these plants are used for medicinal and stimuli purposes. The roots, shoots, and flowers are quite fragrant, which makes them an attractive, impressive marginal.

Water plantain (Alisma plantago-aquatica)

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Water plantain

Zones: Three to 10.

Exposure: Full sun to part shade.

Height: 457 to 609 mm (18 to 24 in.).

Planting depth: Moist soil to submerged conditions. A native North American water plant, they flower mid-summer bearing small white-pink petals, which last roughly two days. One of the first to have foliage in the spring, these lush marginals are at home in or beside the water. With this plant, versatility is important.

Golden sword

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Golden sword

Zones: Six to 11.

Exposure: Full sun to part shade.

Height: 762 to 1219 mm (30 to 48 in.).

Planting depth: Moist soil and will tolerate standing water during the summer months. Golden sword rushes are native to Australia and have cylindrical leaves with extremely thick cuticles that have a distinct yellow stripe running its length. These plants are ideal for streamside planting.

Hop sedge (Carex lupulina)

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Hop sedge

Zones: Four to 11.

Exposure: Full sun.

Height: Up to 914 mm (36 in.).

Planting depth: Moist soil to 25 mm (1 in.) of standing water. These unique sedges are renowned for their spiky, lime-green seed spikes, which form over mid- to late-summer. This plant is a hearty feeder and, thus, provides good filtration for ponds with excess fish and/or nutrients.

Bowles’ golden sedge

Zones: Five to 10.

Exposure: Full sun to part shade.

Height: Up to 914 mm (36 in.).

Planting depth: Moist soil and will tolerate standing water during the summer months.

Button bush (Cephalanthus occidentalis)

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Button bush

Zones: Five to 10.

Exposure: Full sun.

Height: 1.8 to 6.1 m (6 to 20 ft).

Planting depth: Moist soil and will tolerate standing water up to 152 mm (6 in.). Button bushes are a temperate North American native shrub with dense, rounded heads (up to 25 mm [1 in.] across) comprising small, fragrant, tubular, funnel-shaped, white-to-cream flowers with red veined and mid-ribbed green leaves.

Dwarf water bamboo

Zones: Six to 10.

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Dwarf water bamboo

Exposure: Full sun to part shade.

Height: Up to 457 mm (18 in.).

Planting depth: Moist soil and will tolerate up to 102 mm (4 in.) of standing water. Although not a true bamboo, the upright green leaves and stocks resemble their namesakes and form non-invasive, dense clumps. A heavy feeder, this plant is best to fertilize regularly.

Rush plants

These plants fulfil an important function in the shoreline area to a water depth of approximately 508 mm (20 in.). Not only do they consume nutrients that are released by sinking biomasses (e.g. leaves, seeds, flower petals, pollen, etc.), they also take care of the air-gas exchange when the pond is frozen during the winter. Through the dry stalks, gases like methane escape, allowing oxygen to enter the pond. Tall plants like reeds, rushes, bur-reeds, also serve as sight protection for the waterway. Here are some specimens:

Cotton grass (Eriophorum)

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Cotton grass

Zones: Four to seven.

Exposure: Full sun to part shade.

Height: Creeping 152 to 205 mm (6 to 12 in.).

Planting depth: Moist soil and will tolerate up to 25 mm (1 in.) of standing water. This is a lush green grass-like plant that produces downy tufts of bright white seed heads in the summer.

Mare’s tail (Hippuris)

Zones: Four to 10.

Exposure: Full sun.

Height: 152 to 305 mm (6 to 12 in.).

Planting depth: Moist soil to submerged conditions. These aquatic plants resemble horsetails superficially, but are not hollow and produce small flowers.

Gold strike reed

Zones: Three to 11.

Exposure: Full sun to part shade.

Height: 305 to 610 mm (12 to 24 in.).

Planting depth: Moist soil and will tolerate being submerged up to 76 mm (3 in.). This variegated cultivar is a natural addition to most NSPs.

Corkscrew rush (J. effusus, J. filiformis, and J. inflexus)

Zones: Four to nine.

Exposure: Full sun to part shade.

Height: Up to 457 mm (18 in.) (creeping), while J. effusus ‘Unicorn’ are more upright and can reach heights of 610 mm (24 in.).

Planting depth: Moist soil and will tolerate being submerged up to 152 mm (6 in.) during the warm summer months. During mid-summer, the long spiral stems will begin to develop abundant seed heads, roughly 25 mm (1 in.) from the growing tip. This adds to the already cryptic nature of the plant’s form, as well, when submerged, these seed heads often form new miniature replicas of the mother plants. No NSP or water feature is complete without some form of Corkscrew rush and, with the many varieties available, there are plenty to select from.

Cardinal flower (Lobelia cardinalis)

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Cardinal flower

Zones: Five to nine.

Exposure: Full sun to part shade.

Height: 610 to 1219 mm (24 to 48 in.).

Planting depth: Moist soil. Cardinal flowers were first discovered in Canada in the 1600s by French explorers. During the summer, Lobelias send up red blooming towers of showy, vibrant petals which make these plants impressive in any NSP.

Dwarf water clover

Zones: Six to 11.

Exposure: Part shade to full shade.

Height: Up to 101 mm (4 in.).

Planting depth: Moist soil and will tolerate a water depth of approximately 51 mm (2 in.). This four-leaf clover, a close relative to the ferns, is ideal for table-top or bowl water gardens. It is also often the first to have foliage in the early spring.

Variegated water clover

Zones: Five to 11.

Exposure: Partial shade.

Height: Grows along the surface of the water.

Planting depth: Should be submerged approximately 102 to 152 mm (4 to 6 in.) over the crown, allowing the leaves to float on the pond or bowl surface. This lovely four-leaf clover has mottled-green centred leaves with large, rounded lobes. This plant provides an excellent cover for fish, should this be what the owner wants.

Upright water clover (Marsilea quadrifolia)

Zones: Six to 10.

Exposure: Full sun to part shade.

Height: 152 to 305 mm (6 to 12 in.).

Planting depth: Moist soil and will tolerate a water depth of 51 to 102 mm (2 to 4 in.). This exquisite clover grows atop long reddish-brown stems that stand upright out of the water or damp soil. Native to Europe and northern Asia, Upright clover is also a creeping plant, providing excellent cover and garden density with its lush-green foliage.

Curly-leaf mint

Zones: Six to nine.

Exposure: Part shade.

Height: Up to 305 mm (12 in.).

Planting depth: Moist soil and submerged conditions up to 152 mm (6 in.). This mint, much like regular mint, is an extremely fragrant, ornamental marginal. These plants attract wonderful butterflies in the summer and the aromatic leaves can be used for seasoning. This is a pleasant marginal to have growing poolside or in a bowl on a patio.

Bog bean (Menyanthes trifoliate)

Zones: Three to eight.

Exposure: Full sun to part shade.

Height: Up to 305 mm (12 in.).

Planting depth: Moist soil and submerged conditions up to 203 mm (8 in.). This herbaceous perennial has three-palmate dark green leaves growing from the creeping stem, with short, erect racemes comprising 10 to 20 white fringe-edged flowers. These flowers are pink in bud, pinkish white when opening, and white in full bloom. One of the first marginal plants to flower, Bogbeans have been popular in North American water gardens for years.

Floating plants

These plants fulfil an important task in a NSP as they shade the water to keep it cooler, which is especially important in sunnier locations. They offer light and nutrient competition for algae and give living space to many water-cleaning organisms. Floating plants thrive well in mesotrophic waters, but also in oligotrophic environments if they are provided with enough nutrients, or nutrient-rich moist soil in their root area. In the case of water lilies, all species prefer mesotrophic/eutrophic water and substrata; they make no special demands on the water quality if it does not show extreme pH values. They grow in calcium-rich, poor aquatic environments as well. All water lilies need sunlight—six hours per day—to unfold their floral splendour. Only the pond roses can get by with little sun and thrive in the shade.

Floating plants are unique as they require no potting and, thus, no soil. They simply float on the pond’s surface and remove excess nutrients in the water, keeping the rest of the pond clean and clear. The roots of floating plants provide excellent biological and mechanical filtration. These plants seem to have it all, while being relatively maintenance-free. The following are some examples:

Water hyacinth (Eichhornia crassipes)

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Water hyacinth

Zones: Nine to 11.

Exposure: Full sun to part shade.

This plant has bulbous, air-filled sacs, ending in rosettes of glossy-green leaves. A tropical perennial, water hyacinths have large lilac/bluish flowers that are delicate, lasting only one to two days. An aggressive feeder with long, filamentous purplish roots, these lush floaters are probably the most popular floating plant and are in high demand during the summer months. An excellent filter plant, especially suited for pond life, they stay flat and level with the water’s surface. This is ideal, as hyacinths will brown and perish if turned upside-down and submerged.

American frog’s-bit (Limnobium spongia)

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American frog’s-bit

Zones: Eight to 11.

Exposure: Full sun to part shade.

Frog’s-bit has small, spiny-type flowers in mid to late summer, although the dark-green, spongy floating leaves are what makes this plant attractive. If the NSP includes fish, be aware as they may nibble on the outer edges of the leaves.

Water lettuce (Pistia)

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Water lettuce

Zones: Nine to 11.

Exposure: Part sun to part shade.

Water lettuce has lush, lime-green leaves arranged in spirals. This tropical floater is highly susceptible to frost, but makes a great summer addition for large NSPs to small bowls.

Salvinia natans (Large Salvinia)

Zones: Nine to 11.

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Salvinia natons

Exposure: Part sun to full shade.

This unique aquatic fern grows in whorls of three leaves, each bearing fine silky hairs. Not readily eaten by fish, Salvinia natans provide near-perfect surface cover.

Salvinia rotundifolia (Small Salvinia)

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Salvinia rotundifolia

Zones: Nine to 11.

Exposure: Part sun to full shade.

A smaller, more round form of Salvinia, this floating fern grows in less defined sections and seems to free-float more than its larger counterpart.

Planting water lilies and winter-hardy water lilies

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Each lily should have approximately 1 m (3.2 ft) for growth and sustainability. Prior to purchasing, determine if the species selected spreads quickly or is less expansive. If stunted growth is desired, this can be done by building up stones fist-or head-high around a water lily bed to hinder its expansion. More than 450 varieties of water lilies are on sale worldwide. Of course, not all are ideally suited to every climate. Therefore, choose types that have been raised for generations in the climatic zone where they are to be planted.

water lily[16]
More than 450 varieties of water lilies are on sale worldwide; however, not all are ideally suited to every climate.

Hardy water lilies are defined as water lilies that can tolerate winter temperatures provided the rhizome itself does not freeze. Six main colour varieties dominate the hardy water lily landscape: red, pink, white, yellow, peach/orange, and changeable. Most varieties can be traced back to a cold-water Nymphaea native to mountain lakes in Sweden. As such, these particular water lilies are extremely tolerant of temperate climates and grow very well in zones four to 11. From spring to fall, single flower buds—often many per plant—will rise from the base. Like clockwork, opening mid-morning and closing at night, these flowers last three to four days and are continually replaced by new flower buds arising from the depths.

The underwater plants

Underwater plants as the name suggests are well-suited to the aquatic environment; the stems and leaves are flexible and have air chambers that lift them. With their entire plant body, they take nutrients directly from the water, serving mainly to anchor the plants to the bottom. Submersed plants are the best nutrient competition for algae and give off various materials that halt algae development (alleopathy). These underwater plants should be found in every pond, since they do the following ‘jobs:’

There are more than 25 types of underwater plants (i.e. submersed macrophytes) that can be used in NSPs. Do not scrimp on this plant group as they work against algae formation from the beginning.

Oxygenators, one of the most important pond plants of them all, are also often the most overlooked. Either free-floating or rooted, these essential plants not only provide much-needed air for a healthy pond, they also filter water, provide cover for fish and other pond life, act as a main food source for fish—directly and indirectly—and most importantly, they compete for the same nutrients as algae. Absorbing nutrients through their leaves and stems, oxygenators keep the water clean and clear, while algae blooms are eliminated. Any pond containing fish will not be a healthy pond unless it is well-stocked with oxygenators.

Because oxygenating plants acquire nutrients from their leaves and stems, they can often be planted in gravel. Those without roots do not need to be planted at all. Quite simply, these plants can be the easiest to maintain in a NSP. Here are some popular specimens:

Brazilian waterweed (Egeria densa)

Zones: Six to 11

Exposure: Part sun, part shade.

Planting depth: Grows fine as a free-floating aquatic oxygenator, but can also be planted 152 to 457 mm (6 to 18 in.) below water into soil or gravel/sand. Anacharis is great for aerating the water, as well as algae control and fish cover.

Canadian pondweed (Elodea Canadensis)

Zones: Three to 10.

Exposure: Full sun to part shade.

Planting depth: Grows fine as a free-floating aquatic oxygenator, but can also be planted 152 to 457 mm (6 to 18 in.) below water into soil or gravel/sand. Elodea is a great NSP oxygenator and is a well-used staple.

Hornwort

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Hornwort

Zones: Four to 10.

Exposure: Part sun (direct sunlight may burn exposed tips).

Planting depth: A free-floating aquatic oxygenator, Hornwort is a complete aquatic plant with thinly branched, bristly leaves that fork out underwater.

Parrot feather (Myriophyllum aquaticum)

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Parrot feather

Zones: Six to 10.

Exposure: Full sun to part shade.

Planting depth: Parrot feathers are a submerged oxygenator that can be planted in soil or bare-rooted in water. Bright blue-green, feathery foliage sits upright at the water’s surface, sometimes up to 305 mm (12 in.) high. This plant is excellent for water filtration and aeration.

Sagittaria subulata

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Sagittaria subulata

Zones: Eight to 11.

Exposure: Full sun to part shade.

Planting depth: These plants can be submerged up to 610 mm (24 in.) over the top of the pot. This sagittaria is a vigorous producer of showy, multi-headed white flowers with green-yellow centres. They can be planted pond side, in shallow water, or medium water depths.

Dwarf parrot’s feather (Myriophyllum sp.)

Zones: Six to 11.

Exposure: Full sun to part shade.

Planting depth: These plants can be submerged up to 305 mm (12 in.) and are also free-floating. Dwarf parrot’s feather may be less vigorous than the larger, nominate variety, but they are just as hardy. Two popular cultivars are available in the red-stemmed variety and a spiny, lance-shaped variety termed ‘propium.’

Planting the vegetation

Plants are set in prepared beds that are filled with specific NSP substrate, which should be supplied with meager nutrients and trace elements. Since they need fine soil, the substrate at these places is best covered with 0 to 8 mm (0 to 0.3 in.) or 0 to 16 mm (0 to 0.6 in.) screened gravel, but not deeper than 1 mm (0.04 in.).

Plant life in NSPs play a vital role in creating a healthy environment by ensuring proper water balance, cleanliness, and enjoyment for not only the end-users, but also for micro-organisms and wildlife. The proper use of indigenous plants for the zone and hardiness will allow the waterway to balance with ease.

 

Winkler_HeadshotMarkus Winkler is the master designer and lead strategist for PoolsByNature, a designer/builder of natural swimming pools (NSPs) in Kelowna, B.C. He has more than 12 years of experience in the field of NSPs. Winkler has an engineering background in electronics and has received extensive education with respect to environmental and aquatic applications. He can be reached via e-mail at poolbynature@gmail.com[20].

 

 

 

Williams_HeadshotKaren J. Williams is the design analyst for PoolsByNature. She has more than 20 years of experience in environmentally sustainable product strategies and is a member of the design team responsible for the connection between licensee partnerships and end-users while working with the company’s master designer.

Endnotes:
  1. [Image]: http://poolspamarketing.com/wp-content/uploads/2014/06/DSC_0329.jpg
  2. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/Variegated-sweet-flag_cropped.jpg
  3. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/water-plantain_cropped.jpg
  4. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/golden-sword_cropped.jpg
  5. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/hop-sedge_cropped.jpg
  6. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/button-bush_cropped.jpg
  7. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/Dwarf-water-bamboo_cropped.jpg
  8. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/cotton-grass_cropped.jpg
  9. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/cardinal-flower_cropped.jpg
  10. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/water-hyacinth_cropped.jpg
  11. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/americans-frog-bit_cropped.jpg
  12. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/water-lettuce_cropped.jpg
  13. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/salvinia-natans_cropped.jpg
  14. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/salvinia-rotundifolia_cropped.jpg
  15.  : http://www.poolspas.ca/wp-content/uploads/2015/05/water-lily.jpg
  16. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/water-lily.jpg
  17. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/hornwort_cropped.jpg
  18. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/parrot-feather_cropped.jpg
  19. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/sagittaria-subulata_cropped.jpg
  20. poolbynature@gmail.com: mailto:poolbynature@gmail.com

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