How to Plant a Pool

Planting is probably the most important part in establishing your pool and it is often the most neglected. A pool cannot be successful without a full complement of aquatic plants, an under planted pool will usually remain green or cloudy unless you invest in a biological filtration with an ultra violet clarifier, without which, makes it difficult to see your fish except when they are near to the surface.

Pools should be planted when the plants are in their growing season, which is normally from late March to the end of September. If the pool has been filled with tap water then allow this to stand for a few days to allow Chlorine and other chemicals to disperse. It is important that the aquatic plants be given at least three weeks to establish before introducing any fish.

Water plants should be planted in open sided baskets; except for water lily tubs, which are generally solid. The baskets should first be lined with basket liners to prevent soil erosion then filled to within 1″ of the rim with Stapeley’s own aquatic soil, which has at least 60% clay content. The intended plant should be trimmed if necessary, a hole is made in the middle of the soil with your hand and the plant placed in the soil so that the top of the soil of the plant is the same level as in the basket, firm the soil around the plant and push a couple of plant food tablets deep into the soil. Trim the excess basket liner then top of the soil with well washed aquatic gravel, this will help to prevent the fish from digging into the soil.

To help with selecting which basket to purchase, refer to this chart below.

o Mini round-1 small marginal or 5 bunches of oxygenators

o Mini square- 1 small marginal or 5 bunches of oxygenators

o Medium round- 1 marginal, 10 bunches of oxygenators or 1 small water lily

o Small square- 1 marginals, 10 bunches of oxygenators or 1 small water lily

o Medium square- 1 or 2 marginals, 10 bunches of oxygenators or 1 small water lily

o Large square- 1 or 2 marginals, 15 bunches of oxygenators or 1 medium water lily

o Contour- 1-3 marginals or 15 bunches of oxygenators

o Lily tub- 1-3 larger marginals, 20 bunches of oxygenators or 1 medium or vigorous water lily

o Jumbo lily tub- 50-100 bunches of oxygenators or 1 vigorous water lily

The basket/tub should be placed into the pool in accordance to the type of plant it is (further details will be given later on). Avoid placing any plant basket too near moving water as the soil could be eroded and avoid putting lilies where fountains can splash them. Marginal plants look better in bold groups rather than individually, with the taller ones near the back of the pool and the lower growing ones near to the front.

It is difficult to give exact numbers of plants required for your pool, however, a guide to plant numbers can be found at the appropriate plant section.

Aquatic plants are divided into five main categories, these are: –

Oxygenating plants

Oxygenators are essential for all pools; the water is unlikely to clear until these plants are growing vigorously and in quantity. Without oxygenators, pools turn to a green pea-soup colour, this is caused by millions of microscopic, free floating single cell plants we call algae.

Algae flourish under the influence of sunlight and excess mineral salts present in the water. In time, oxygenators should compete for light and nutrients and literally starve the algae to death producing clear water. Apart from clearing the pool, oxygenators provide a supplementary food source for fish; they also provide a spawning medium and hiding place for fish, amphibians and insects. Oxygenators are sold either already potted up or as unrooted cuttings, which should be planted up and be placed, eventually, at the bottom of the pool.

Oxygenators- allow 5 bunches per 1 sq. metre of water surface

Water Lilies

These are without doubt the queens of the pool; these most beautiful of plants come in five colours, white, red, pink, yellow and changeable/copper. They can flower from June to October with often, a constant succession of blooms, each lasting for 3-5 days and some providing a delicate perfume.

Whilst most water lilies are cultivated for their beautiful flowers, the leaves of some varieties are also very pretty, with their striking tiger stripes or delicate mottling, water lily leaves also provide shade for fish and cut down the amount of sunlight reaching the water surface helping to control algae growth. Varieties vary in size from the dwarf ‘Pygmaea Helvola’ that has leaves often the size of a fifty pence piece and can grow in 6″ of water, to the giant ‘Gladstoneana’ with its 18″ diameter leaves; this variety can eventually live in 1.2 metres of water.

Care must be taken when selecting your water lily as the wrong choice could lead to the plant either being too big or too small for the pool, the ideal coverage rate for a water lily is approx 65-75% of the water surface; the coverage rates for each size of water lily is shown below. As an example, I have a pool 2 metres wide and 3 metres long (6 sq. metres in total), so I need a lily which will cover approx 65-75% of this amount of surface, (approx 4 sq, metres) so I need 1x medium/vigorous (m/v) water lily or 2 x small/medium (s/m) ones

o Water lilies- miniature (T)- allow 1 plant per 1 sq. metre of water surface

o Water lilies- small- allow (S) 1 plant per 1.5 sq. metres of water surface

o Water lilies-small-medium (S/M)- allow 1 plant per 2 sq. metres surface

o Water lilies-Medium (M)- allow 1 plant per 3 sq. metres of water surface

o Water lilies- medium/vigorous (M/V) allow I plant per 4 sq. metres of water surface

o Water lilies- Vigorous (V) allow 1 plant per 5 sq. metres of water surface

The depth water lilies should be planted will depend on the variety; all planting depths are measured from the water surface to the crown of the plant or soil level; –
Initial depth is the recommended planting depth for a new or young plant.
Optimum depth is the recommended long term planting depth, which would allow for optimum growth under ‘typical’ conditions.

Maximum depth specifies the recommended maximum depth, which a mature lily will survive at, but may only apply when assuming clear water and full sun.


Miniature (T) Initial Depth 8cm – Opt Depth 16cm – Max depth 24cm

Small (S) Initial Depth 10cm – Opt Depth 20cm – Max depth 30cm

Small/medium S/M) Initial Depth 12cm – Opt Depth 24cm – Max depth 36cm

Medium (M) Initial Depth 15cm – Opt Depth 30cm – Max depth45cm

Medium/vigorous (M/V) Initial Depth 20cm – Opt Depth 40cm – Max depth 70cm

Vigorous (V) Initial Depth 25cm – Opt Depth 50cm – Max depth 90cm

Ideal water lilies for small pools- 2 sq. metres

– Caroliniana Nivea

– Laydekeri Lilacea (Pink)

– Froebelii (Red)

– Odorata Sulphurea (Yellow)

Ideal water lilies for medium sized pools – 5 sq metres

– Marliacea Albida (white)

– William falconer (Red)

– Marliacea Chromatella (Yellow)

– Gladstoniana (White)

Ideal water lilies for large pools- 8 sq metres +

– Colossea (Pink)

– Colonel A. J. Welsh (Yellow)

– Alba (White)

Marginal plants

These plants, in most cases will grow, both in damp soil and in waterlogged conditions with varying depths of water over the planting soil. In smaller pools there are a number of marginals that will help to provide some surface coverage and their roots will absorb waste nutrients. Marginals, however, are essentially decorative, with plants such as Iris and reeds providing a formal effect or symmetry in the pool. Alternately a more natural or informal effect can be produced using a mixture of vertical and clump forming plants to soften the edges between the pool and the rest of the garden. A pool without marginals may look flat and lifeless, marginal plants break up the flatness and provide a background to your water lilies.

When selecting marginals, like any other plant, pay attention to the any flowering period, flower colour, as well as the plant shape, texture, colour or height. Unless you are planting a formal pool, try to avoid planting marginals in even spaces and lines like soldiers, instead place different plants side by side for contrast or clumps of the same plant to form impressive displays, and have uneven gaps between others.

Like water lilies, most marginals appreciate full sun and occasional feeding, also when first planting marginals it is best to lower them slowly to their ideal depth (any planting depths given in our literature or on the web is measured from the top of the planting soil to the top of the pond).
Marginals- allow 1-2 plants per metre of shelf

Ideal marginal plants for the smaller pool.

o Caltha Palustris plena (Double marsh marigold)
o Calla palustris (Bog arum)

o Eriophorum angustifolium (Cotton grass)

o Geum rivale (Water avens)

o Iris setosa (Dwarf iris)

o Menyanthes trifoliata (Bog bean)

o Sparganium erectum (Burr-reed)

o Typha minima (Dwarf reedmace)

Ideal marginal plants for medium pools

o Acorus calamus (Sweet scented rush)
o Caltha Palustris (Marsh marigold)

o Alisma plantago (water plantain)

o Houttuynia cordata variegata (Chameleon plant)

o Iris ensata (Japanese water iris)

o Lobelia cardinalis ‘Queen victoria’

o Lysichiton camchatcensis (Japanese skunk cabbage)

o Persicaria amphibia (Amphibious bistort)

o Sagittaria japonica (Japanese arrowhead)

Ideal marginal plants for larger pools

o Caltha palustris var. palustris (Giant Marsh Marigold)

o Carex pendula (Drooping sedge)

o Cyperus longus (Sweet galingale)

o Iris pseudacorus (Yellow flag Iris)

o Pontederia cordata (Water pickerel)

o Ranunculus lingua ‘Grandiflorus’ (Greater spearwort)

o Schoenoplectus (Scirpus) tab. ‘Albescens’ (Bulrush)

o Schoenoplectus (Scirpus) tab. ‘Zebrinus’ (Zebra rush)

o Typha angustifolia (Lesser reedmace)

o Typha Latifolia (Greater reedmace)

o Zantedeschia aethiopica ‘Crowborough’ (Arum lily)

Buying Marginals

Marginals can now be purchased in 9cm pots, 1 litre baskets, 2 litre baskets, 3 litre baskets and occasionally as specimens in lily tubs, the smaller the pot size, the younger the plant, young plants will need to be given time to become a decent size and will eventually catch up with the older plants. 9cm plants need to be taken out of their pots and planted into medium sized planting baskets using Stapeley’s own planting compost which has been specially formulated for aquatic plants. 1 and 2 litre plants are OK for the first year then will need to be planted as per 9cm plants. Although it is difficult to accurately recommend how many marginals to use, we generally say between 1 and 2 per 1 metre of shelf depending on the overall effect desired.

Deep Marginal Plants

This category of plants are essentially the same as water lilies in as much that they are planted some way below the surface and generally have leaves on or above the surface, however, they are usually mentioned separately. Deep-water marginals are planted in medium to large planting baskets in Stapeley’s own planting compost and lowered slowly over a few weeks to their ideal depth.

Recommended varieties (Deep marginals)

o Aponogeton Distachyos (Water hawthorn)

o Nuphar lutea (Brandy bottle lily)

o Nymphoides peltata ‘Bennettii’ (Water fringe)

o Orontium aquaticum (Golden club)

Floating plants

Floating plants can be split into two basic groups; the first group contains the hardy plants, which are beneficial in small to medium pools, as they will quickley provide the valuable cover required to reduce algae growth plus their roots utilise waste nutrients in the water. Some of these plants could eventually cover the whole pool but all you have to do is occasionally remove any excess growth with a fish net. Lemna (Duckweed) and Azolla (Fairy moss) should be avoided in large pools, as their management will be more difficult.

Typical hardy floating plants

o Azolla filliculoides (Fairy moss)

o Hydrocharis morsus ranae (Frog-bit) not normally available until early May.

o Lemna minor (Common duckweed)

o Lemna trisulca (Ivy leafed duckweed)

o Straitiotes aloides (Water soldier/cactus)

The second group contains the tender, tropical floating plants, which look very attractive in the summer months, but which usually don’t spread enough to provide much cover. These plants should be treated as annuals as they will die off in the first frost, it is very difficult and not economical to try and keep them alive over winter. Introduce as many plants as you choose from this group. Water hyacinth and Water lettuce are excellent at removing excessive nutrients, so much so that they are used in huge filtration plants in certain parts of the world, they are also good at removing heavy metals from drinking water.

Typical tender floating plants

o Eichhornia crassipes (Water hyacinth) not normally available until end of May

o Pistia straitiotes (Water lettuce) not normally available until end of May

Floating plants- allow 1 plant/portion per 1 sq. metre of water surface

Moisture loving/Bog /Poolside plants

Whilst the ground immediately surrounding most pools will be constantly damp in nature, this does not follow in the garden when using a pool liner, if this area dries up during the summer then a polythene liner can be placed 30-60cm under the soil to hold moisture (poke holes in the base to avoid water logging), alternatively, water on a regular basis to avoid drying out. These plants are mostly in 9cm pots but a few are also available in 1-litre pots. Certain varieties such as lobelia cardinalis, Lysimachia nummularia and Zantedeschia aethiopica are very tolerant and are sold as marginals too.

Ideal plants for a small poolside area

o Adiantum pedatum v. subpumilum (Dwarf evergreen fern)

o Asplenium trichomanes (Evergreen fern)

o Lychnis flos-cuculi (Ragged robin)

o Persicaria affine ‘Donald lowndes’

o Primula auricula

o Primula veris (Native cowslip)

o Primula vulgaris (Native primrose)

Ideal plants for a medium sized poolside area

o Achillea ‘Walter funcke

o Astilbe

o Dicentra spectabilis (Bleeding heart)

o Hosta undulata var. albo-marginata

o Iris sibirica ‘Snow queen

o Lobelia cardinalis ‘Queen victoria’

o Lythrum salicaria (Purple loostrife)

Ideal plants for a large sized poolside area

o Crocosmia ‘Lucifer’

o Darmera peltata (umbrella plant)

o Dryopteris felix-mas (Male fern)

o Filipendula ulmaria (Meadow sweet)

o Gunnera manicata

o Hosta Halycon

o Ligularia dent. ‘Desdemona’

o Osmunda regalis (Royal fern)

o Rheum palmatum (Giant rhubarb)