By Markus Winkler and Karen J. Williams
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)
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)
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
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)
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.
