Choosing and growing water plants in a wildlife pond
Even the smallest garden can accommodate a small pond, and if you have a large garden, the possibilities are endless. You can do nothing better to encourage wildlife than providing it with water, and you will be amazed at how quickly wild creatures – birds, small mammals, amphibians like frogs and newts, countless insects, molluscs and water-creatures – will visit or colonise your pond if you provide them with water, and the larger the pond the better. Mid-spring to early summer is the perfect time for planting up a pond, but now we’re all in lockdown, you’ll probably have time to make the pond too.
Be aware that small children can drown in just a few inches of water, so you will need to place a grid just under the water if children under about six are to use the garden.
If you want to keep fish such as koi carp in your pond, it will not be so good for wildlife, as fish are predators. They are much more suitable for a formal pond, nearer the house; this will also make feeding the fish easier in bad weather. Unfortunately, koi and other fish attract herons, so you may need to take preventive measures if these are likely to be a problem. (Herons will also prey on amphibians in a wildlife pond, but there will be far more opportunities for them to escape.) Fish-ponds are also better fitted with a filtration system, which is not necessary in a wild-life pond.
In larger gardens, first choose a site for your wildlife pond. Some people feel that a pond should be sited at the lowest part of the garden, as a natural pond would be, but this is not written in stone, and you may know exactly where your pond should go – it’s lovely to be able to see the pond and the wildlife from the house, where you will not disturb it. Choose a sunny spot, or one where most of the pond is in sun for most of the day; shady ponds are not good for wildlife generally, although small mammals and birds are unlikely to mind. That is not to say that the water should be exposed to the sun’s rays – you want 65-75% of the surface covered in water-plants, to keep the water cool and provide a refuge for the pondlife. Overhanging trees not only over-shadow the pond, but fill it with fallen leaves in autumn, which increases the nutrient level and means more maintenance. It’s also important to choose a level site, to prevent nutrient-rich run-off into the pond.
It is possible to dig out a pond and line it with puddled clay, but it’s easiest to line it with heavy butyl liner. There are lots of online guides to making a pond, and I would suggest looking at a few before you start, but here are a few basic tips. Keep the shape natural-looking and simple. The depth in the centre should be at least 60cm/2’ to prevent freezing in winter, and in a very large pond as deep as 90cm/3’. Your pond will look much more natural if you construct a ‘shelf’ (also level) about 15cm/6”– 20cm/8” below the edge of the pond for marginal plants around most of the perimeter. In a deep pond include a deeper ‘shelf’ at 60cm/2’. There must also be a ‘shallow end’, very gently sloping up from the centre of your pond to the edge, to allow birds access for drinking and bathing, and small creatures unlucky enough to fall in to escape – this looks particularly attractive if you make a ‘beach’ of very smooth, rounded pebbles sloping gently up and onto the outside of the pond. Make sure that the sides are absolutely level, using a spirit level on a long plank running from side to side and along the length. When you’re happy with the shape and levels of your pond, remove any stones, firm up the inner surface of your pond well, and then line it.
Butyl liners must be laid over a special underlay, or stones will rise from the depths of the soil and puncture it; the underlay will also allow a bit of ‘give’ to the liner if something sharp falls into the pond. At least 30cm/1’ of the liner should overlap the pool; weigh this down with the sods you removed when digging the pond out, until the liner is correctly fitted against the underlay, and then fill your pond. Rainwater is ideal, siphoning it from your rain-barrels; well-water is usually fine; tap water, especially hard water, is a last resort. The pressure of the water will ease the liner into its final position, and the sods, being fairly light, will allow the liner to sink back in to fill any gaps if necessary.
When the pond is full, sink the edge of the liner into a slit trench, firm it in and cover it with smooth stones, pieces of wood or similar things which will provide hiding places for wildlife. If you want a bog area round the pond, dig it out and line it with excess pieces of butyl liner, perforate them in just a few places – you want it to drain only very slowly – and then fill it with soil.
Now add some smooth, rounded pea-gravel to the bottom of your pond and the shelves, for self-sown water-plants to attach to, and again, to give a more natural look – no one really wants to contemplate a butyl liner. Let the pond settle for a day or two, and then comes the exciting bit – planting it up!
Planting your pond
Buy your plants from a reputable supplier like Future Forests – you can choose from a wide range and see pictures and planting advice on the website. Never collect from the wild or take some from a friend’s pond, as there are some horribly invasive water-plants that can hitch a ride undetected and choke your beautiful new pond.
There are four basic types of plants for ponds: oxygenators, ‘floaters’, deep-water plants like water-lilies, and marginal plants, which revel in boggy soil or shallow water.
Oxygenators are important for keeping the water well oxygenated and clear. The following are all native. Whorled water milfoil (Myriophyllum verticillatum) can be grown in ponds up to a metre deep; lobed emergent leaves and rather insignificant flower spikes above the surface. Greater water-moss (Fontinalis antipyretica), also known as willow moss, is our largest aquatic moss, forming an underwater clump which will tolerate occasional drying out. Hornwort (Ceratophyllum demersum) will grow in deep water, its long, feathery fronds floating freely. All these need to be anchored down with a smooth stone, although some come as pre-weighted bunches. The mat-forming dwarf hair grass (Eleocharis acicularis) will tolerate depths up to 60cm/2’, and has spiky brown flowers in late summer and early autumn; it can also be grown in a bog area. Common spikerush (Eleocharis palustris) has attractive seedheads, and can be grown at a depth of just 6cm/2 ½” – on a brick on the pond’s ‘shelf’, or in boggy ground round the edge. Also good are common water starwort (Callitriche stagmalis) and spiked water milfoil (Myriphyllum spicatum) which has tiny red flowers held above the water and can be planted as deep as 1m/3’3”. At all costs, avoid parrot’s feather (Myrophyllum aquaticum) and Canadian pondweed (Elodea canadensis), as these are horribly invasive.
Floaters also help keep the water clear, and don’t need anchoring. A good native plant is delicate frogbit (Hydrocharis morsus-ranae) with little white flowers and water-lily-like leaves that float on the water. Water soldier (Stratiotes aloides), which is especially good at preventing algal growth, is also thought to be native, but may have been introduced in the early 19th century; it has rosettes of narrow leaves and a single, white, three-petalled flower. Avoid the invasive duckweed (Lemna species) and fairy moss (Azolla filiculoides), which can quickly choke your pond.
These include beautiful water lilies and water hawthorn. Not all of these are native, but they’re lovely, non-invasive, water-shading plants for planting in aquatic baskets in the deeper water. Water hawthorn (Aponogeton distachyos) with its floating leaves has the great advantage of producing its scented, white, bee-attracting flowers early in the year, and continuing until the frosts with a brief gap in August.
Native or long-introduced water-lilies include the familiar brandy-bottle or yellow water-lily (Nuphar lutea – good for pollinators) and the gorgeous white water-lily (Nymphaea alba) Ireland’s only true native. There are also many stunning water-lily cultivars available – choose from pink, red, white and soft yellow varieties, as you please – some, like Nymphaea Aurora, even change colour during their brief but beautiful life.
Water-lilies need still water and full sun. Their leaves spread over the surface of your pond, cooling the water and providing a safe place for pond-life to hide. There are tender, tropical water-lilies, but in our climate it’s best to pick a hardy one. Choose your water-lily according to the depth of your pond – you need to be careful about the depth they will eventually need, or they won’t flower. Large water-lilies will need a depth of 75cm/30” depth, medium-sized ones 50cm/20” and small ones 20cm/8” (check the website for planting depth).
Water-lilies can be planted between April and September. If they come in an ordinary pot you will need to re-pot your lily into an aquatic pot (see below), choosing a pot size suitable to the vigour and size of your chosen plant. As water-lilies are big feeders, add a slow-release water-lily fertiliser to the compost, unless your aquatic compost contains enough for the first season. Trim off any very long roots and damaged leaves and plant with the rhizome level with the top of the compost. Top the compost with lime-free pea-gravel.
Don’t plant at full depth straight away; rest the pot on smooth bricks at a depth of 20cm/8”, being careful not to harm the butyl liner. Over the next month or so, as your water-lily begins to produce leaves on the surface, gradually remove brick by brick until the plant is at the correct final depth.
Feed your potted water-lily again as it starts into growth each year. It’s best to remove the flowers below the waterline as they go over, and also the faded leaves in autumn; this will help keep the pond clear and sweet. Water-lilies need dividing every five years or so, as they outgrow their container; signs of needing division or potting up include poor or non-existent flowering, leaves above the surface instead of floating on it, or a congested appearance in the pot.
Marginals are plants that love shallow water (here’s where the ‘shelf’ comes in) or thrive in boggy ground, and are wonderful for creating a naturalistic edge to your pond. Native plants include the familiar flag iris (Iris pseudacorus), which happily sits in shallow water, or try its paler or variegated cutivars. Other, non-native, water-loving irises are also good on a boggy margin, including I. ensata, I. louisiana, I. sibirica and the beautiful black I. chrysographes with its delicate gold pencillings.
Smaller native bog plants include creeping Jenny (Lysimachia nummularia) with little yellow flowers, lady’s smock (Cardamine pratensis) and brooklime (Veronica beccabunga which will extend over the water and lap up surplus nutrients). Small native marginal plants that thrive in water include marsh marigold (Caltha palustris – plant in water up to 23cm/9” deep) the water forget-me-not (Myosotis scorpioides – plant in water no deeper than 10cm/4”) and bog pimpernel (Anagallis tenella – will grow in very shallow water).
If you have a large pond, think about reeds, sedges and grasses, like reed mace (Typha angustifolia) with its striking cylindrical seedheads, and variegated reed sweet grass (Glyceria maxima var. variegata) but be warned that these are spreaders, only suitable for very large ponds, unless planted in an aquatic basket and divided regularly. The same is true of the horsetails (Equisetum hyemale and E. robusta); these are wonderful for a strong vertical accent, but are invasive and very deep-rooted. The familiar gardener’s garters (Phalaris arundacea var. picta) is also a voracious spreader. Better-behaved are the evergreen sweet galingale (Cyperus longus, plant up to 20cm/8” below water-level) with its graceful papyrus-like flowers, the charming, twisted, evergreen corkscrew rush (Juncus effusus var. spiralis, which can be planted in very shallow water) and flowering rush (Butomus umbellatus) with pretty pink flowers, good for pollinators, and can be planted up to 25cm/10” below water-level.
And don’t forget other perennials that flourish in very moist soil. The Arum lily (Zantedeschia aethiopica) is wonderful beside a pond, and candelabra primroses, Rheum and Ligularia and many, many others can provide beautiful leaves and flowers over a long season. Always go for marginal plants and perennials that are good for pollinators – this is a wild-life pond, after all.
How to plant aquatic plants
Many marginals can be planted directly into boggy ground, but it’s safer to plant plants that actually sit in the water in specialist aquatic compost in aquatic (plastic mesh) baskets, which allow roots to escape through the mesh and to remain wet; line the basket with a piece of hessian to prevent the escape of compost into the water. Aquatic compost is made up of low-nutrient, gritty loam, sometimes containing a slow-release fertiliser that will not leak into the water to raise the nutrient level. You can make your own, but it’s easier to buy proprietary aquatic compost and know that the composition is right. Before you sink the pot into the water, cover the surface with a layer of lime-free pea-gravel. Check the website to see what planting method is best for the plants you choose.
‘Floaters’ like water soldier don’t need to be planted – just lob them in. Some oxygenators just need weighing down with a stone – check the website.
Planting a dry pond margin
If your pond has a dry margin rather than a boggy area, plant any perennial or low shrub that suits your soil and which looks appropriate to a pond edge – Mediterranean plants would not look well here. Plants which lean over the water look particularly lovely; angel’s fishing rod (Dierama pulcherrimum) is gorgeous reflected in the water, but does not like wet soil at all. Grasses can stand in for reeds, and give a vertical accent – Calamagrostis x acutiflora ‘Karl Foerster’ is particularly upright. Among these, plant some lusher, large-leaved plants; ferns would look lovely in the shade.
If you want to stick to native plants, for reliably moist soil choose Lady’s smock (Cardamine pratense) which loves a shadier area, purple loosestrife, meadowsweet, ragged robin and true valerian; try primroses, dog violet, foxgloves, tall mullein and field scabious in drier soils.
Around your pond
In order to attract and protect as much wild-life as possible, have some dense planting at one side of your pond, preferably near the ‘beach’ end. Unfortunately, this can also provide cover for cats, but animals and the shyer birds will generally feel safer if they can approach through cover.
If you have only a patio or tiny garden, you could think of plumbing in a wall fountain, and, if it is a stone wall, encouraging wall plants like ivy-leaved toadflax, rusty-back fern or common polypody to grow on the wall round it. It is safer for small children, birds will come to drink and bathe, and the sound of gently falling water is refreshing to the human occupants of the garden too. A bubble fountain is also safe, and good for attracting birds and small mammals.
A container like an old trough or butler sink with the drain sealed can make a miniature pond, as long as it is 40cm/16” deep (up to 50cm/20” if you want to grow a dwarf water-lily). Big, deep ceramic pots can also make good ponds, as can half-barrels, soaked first to ensure that the wood has swelled until they’re water-tight. Make sure that small creatures can escape the water by providing a bent branch or a few stepped rocks leading out of the container and onto the ground. Surround the container with plants to give cover to the wildlife.
Put some clean, rounded pea-gravel at the bottom, and plant some very small water-plants – no more than three – in aquatic pots, on bricks, if necessary; water forget-me-not and marsh marigold would be suitable. Or grow a single, beautiful, dwarf water-lily like Nymphaea ‘Pygmaea Rubra’ or Nymphaea ‘Pygmaea Alba’; these dwarf water-lilies are only hardy to -5º, but patios close to the house are usually a little warmer than the surrounding area. Be sure to plant an oxygenating plant or two as well.
Read through the notes above for fuller information on how to plant your small pond and for care of water-lilies.
In small ponds you may get algal bloom at first (use a stick to wind it out or clear it with barley straw) but as the pond matures it will usually settle.
Keeping your pond healthy
Algal growth may appear at first, but once you have a good collection of water-creatures, your oxygenating plants hit their stride, and water-lilies and mat-forming marginal plants spread over the surface, things should settle down. A big initial overgrowth of algae can be removed by twisting a stick in it. Barley straw sunk into the pool will also clear the water of excessive algae and keep your pond healthy.
The ideal is to have 65-75% of the water shaded by plants and the rest left as open water. If the pond gets congested with vegetation, rake or pull out some of it, taking it from all levels, so that 25-35% of the surface is clear. Leave what you’ve removed close the pond for a day or two to allow water-creatures to escape back into the water.
If you plant your water-plants in aquatic pots lined with hessian, compost will not cloud your water, but fallen or dying leaves may, adding nutrients which promote algal growth. Dead-head marginal and water-plants, and remove their dying leaves as they fade. You can spread a small-meshed net supported just above the surface of the pond in mid-autumn to catch dead leaves blowing in from the rest of the garden. Black pond-netting is less of an eyesore. If you can’t bear the look of netting, skim off floating leaves daily.
However, a large enough wild-life pond should become a more-or-less self-regulating system, and natural ponds do collect dead leaves. These will eventually rot down and form mud and silt at the bottom of the pond. This can be very smelly if disturbed, but is favourable to some forms of wildlife; however, it may need to be removed every few years or so, especially in smaller ponds. Remove half the silt one year and the other half the next, to preserve the balance of pond-life.
The water-level of your pond can sink in hot, dry weather, but this happens in natural ponds too. If levels get really low, top up with rain-water from a barrel – tap-water is a last resort, as the chemicals with which it’s treated are not good for pond-life.
- Alan Taylor