Water gardening FAQs

What is an ideal site for a pool?

This is rarely achieved, but it should be open, away from trees so that leaves do not fall in it; sunny, to allow the maximum number of flowers to form and open, particularly water lilies; compatible with the landscape of the garden; and fully visible from the kitchen or living room—or from some other vantage point of your choice.

What is the best size for a pool?

Basically, the size (and shape) that seems most suitable for the space available. It should not be so large as to overwhelm the space, nor so small as to be lost in it.

Mark out the proposed site with a thick string or rope to allow for the pool area, and again outside that with another piece of string to allow for any additional plantings. Then stand back and look at it from all angles, especially from the house. If you want a formal pool, it should be in a formal setting. The formal pool looks best with no planting immediately outside it, but an informal one can have planting around it according to the space available.

I am planning a rock garden and wonder whether I might have a pool to go with it.

Certainly—it will give the rock garden extra size in each dimension, increase the scope for another range of plants, and give a more natural appearance to the whole scene. The pool should be built first, and then the rock garden built around at least one side of it.

What can I do with the soil that I dig out to make a pool?

There are various possibilities. You could use the topsoil, usually the top 150 mm (6 in), for areas of the garden where it could improve the growing of plants; or you could stockpile it if you intend to build a rock garden alongside the pool—it will enable you to raise the level of the site. The subsoil which underlies the topsoil can be used to make up height and put at the base of the rock garden, with the topsoil placed on top of it afterwards. If you have no use for the subsoil, hire a skip and have it taken away.

What kind of water-plant container should I buy?

This depends very much on the size and vigour of the plants. If you are to have small ones, a square plastic-basket type, with perforated holes all around and below it, is ideal. If the plants are of a type that will eventually become much larger, a wider and possibly deeper container is essential, otherwise it will be toppled over by wind action on the top of the plant, and its roots will probably outgrow the basket. Almost any container will do, provided that it is at least as broad as it is high; I have used large concrete drains cut in half and placed on end.

I need some good water plants that will grow up to 450 mm (18 in) high. Any suggestions?

The following are excellent: water hawthorn (Aponogeton distachyus), with white flowers with dark spots throughout the year; Acorns gramineus ‘Variegatus’, for foliage colour in green and gold; bog arum (Calla palustris), with white flowers in mid-summer; Caltha palustris ‘Plena’, with double yellow flowers in March-April; Cotula coronopifolia, with yellow ‘buttons’ in July-August; Hydrocharis morsus-ranae, with white-flowered floaters all summer; Mimulus moschatus, with yellow, and M. ‘Whitecroft Scarlet’, with red flowers all summer; golden club (Orontium aquaticum), with yellow club flowers in May-June; and all the medium-sized water lilies (Nymphaea), in red, white, pink, and yellow shades throughout the summer.

Which plants are mainly ornamental?

There are many species. The most obvious are the water lilies (Nymphaea), whose flowers come in a variety of shades of pink, red, yellow, and white and are suitable for various depths of pond. Other plants of various sizes and requiring a constant depth of water include marsh marigold (Caltha palustris), brass buttons (Cotula coronopifolia), monkey flowers (Mimulus species and hybrids), water forget-me-not (Myosotis palustris), pickerel weed (Pontederia cordata), sweet flag (Acorus calamus uariegatus and A. gramineus ‘Variegatus’), and frogbit (Hydrocharis morsus-ranae).

I have a small pool about 3 x 2 m (10 x 6 ½ ft) in area and 600 m (2 ft) deep. What sizes and species of plants would be appropriate?

All the plants mentioned in the previous answer would be suitable; then to add some stature and height I would include one or two of the following: Iris kaempferi, I. laevigata (especially the variegated sorts), /. forrestii, and /. sibirica; flowering rush (Butomus umbellatus), with pink flowers; Pontederia cordata, with blue flowers; Lysichiton camtschatcensis, with white flowers and spreading leaves.

Are there any plants I should avoid in a small pool?

I would avoid the following, all of which are far too vigorous for all but the largest pools or lakes: Alisma plantago-aquatica, most species of Carex except C. stricta ‘Aurea’, Cyperus longus, Lythrum salicaria, Mentha species, Lysimachia uulgaris, L. thyrsiflora, Polygonum amphibium, Potamogeton natans, Ranunculus lingua, Sagittaria species, and Sparganium species.

Do I need fish and other water life to maintain a pool?

No, these are not essential. Most pond inhabitants except fish will soon appear, apparently from nowhere. However, enjoyment of a pool is greatly increased if fish are present. Some I would recommend are showy ones such as golden orfe and goldfish, especially the former, which come to the surface more often. As for other water life, I suggest you could add ramshorn snails (the best scavengers amongst the snails), and if you introduce tadpoles into the pond they will reduce the larvae of pests such as mosquitoes but when they turn into frogs you must provide a means by which they can reach dry land—a gently sloping edge to the pool or, better, some water plants by the edge. >

When is the best time to plant I pool?

In early spring to mid-June, when the weather is warming up—and in any event before you add the fish, otherwise the fish will go hungry unless you feed them yourself. You can plant later if the weather is not too hot but there will be a greater risk, especially to the fish, of a failure to adjust to the changing autumn conditions.

How far below the surface of the water should I position my plants?

This varies with the type of plant. Water lilies, for instance, need to be at the depth at which their leaves will lie flat on the surface, not stick out of the water. Most plants will thrive if the crown (the joint where roots and stem meet) are just covered. Most water-plant nurseries state in their catalogues the planting depth (distance between water surface and crown) of each ot the plants they sell.

How can I propagate my water plants?

This is very simple for most water plants. You just divide them in the spring after lifting out of the containers any plants you require. division is achieved by driving in either two handforks (or two larger forks for larger plants) back to back, then pushing the forks apart to prise away the outermost plants in the clump. Do not use the centre crowns: these are the oldest parts of the plant and should be thrown away. Use a sharp knife to cut water lilies into sections with individual crowns. In some particular cases, as with Mimulus ‘Whitecroft Scarlet’, take soft nodal cuttings.

How do I plant my water plants and what soil should I use?

Let’s take water lilies first. The crowns (tubers or rhizomes) should be planted in a medium to heavy loam with the crown tips exposed and upright—they must not be buried. All other container plants can be planted in the same type of soil and to the same depth as they were at the nursery or when you propagated them.

All planting should be firm, with the roots spread out and excessive or damaged leaves removed. Cover over the soil with chippings or shingle to prevent fish from disturbing it.

The oxygenators will need to be weighted if this has not already been done by the nursery. Clumps of 6-12 small pieces should be put on the floor of the pool and held in a group by a lead weight. This will keep them from floating to the surface. Natural floaters like

Hydrocharis morsus-ranae are simply placed on the surface.

Can you recommend using a fountain in a pool with water plants?

If the plants are marginals and oxygenators, I would say yes. But if they are water lilies or other plants with leaves floating on the surface, you must not use a fountain: the surface will be disturbed, which they will not like, and even if they survive they will rarely flower. This does not apply in a large pool, where water lilies could be located at one end and the fountain at the other.

Which is better, a submersible or an out-of-water pump?

For most small pools the submersible type is preferable. It is easy to instal and produces sufficient power for both the fountain and also a waterfall if you wish to have one. If, however, you want to make a big splash, or have a long connecting pipe, then a non-submerged pump will be necessary; but it is more expensive to buy and to operate.

How do I deal with a leaking pool?

If the pool is made of concrete you should drain it and line it with one of the liners suggested . Before laying the liner, smooth the concrete surface or line it with nylon netting.

If your pool has a polythene liner, it would almost certainly be best and cheapest to renew it completely. But repair kits are available for repairing the more expensive PVC and butyl-rubber sheeting, and your supplier can advise you on repair procedures.

What are the main pests and diseases of pool plants and livestock?

The worst pest of the plants is the water-lily beetle. Its larvae are like small slugs, dark on top and pale underneath. They feed on the leaves of water lilies. The small brown beetles hibernate in the hollow stems of other aquatic plants, which should therefore be cut down in the autumn and burnt You can control the larvae by laying a double thickness of newspaper over all the foliage fron the first appearance of the pest (indicated by holes chewed through the foliage). If this is done in the evening and the papers removed the following morning, and the process is repeated at weekly intervals for at least four weeks, you should find that the beetle larvae will have been eaten by other water life. Remove the worst-damaged leaves. This method of control is also good against the reddish-black aphids which can seriously damage the leaves. Hosing-off the aphids and beetles is also effective—but be careful not to add too much water to the pool .

As far as the fish are concerned, a good balance of water life and a fairly clean pool will go a long way towards preventing most problems; removal and disposal of diseased and injured fish is invariably simpler than treatment. Over-fed fish become constipated and sluggish. Bloated gills, tails, or fins are disease symptoms: remove the fish before the infection spreads. Bloating is due to over-feeding, temperature-shock, or overcrowding. Another disease symptom is a white film that may appear over any part of a fish. This is due to a fungus and usually follows injury. Again, remove the fish from the pool as soon as you see the symptom.

There is a thick green scum on the surface of my pool. What should I do?

If the pool has been filled with water for a matter of only days or a few weeks, remove the worst of the scum (which is formed of algae) with a fine mesh net, but do not change the water: it goes through this stage every time it is filled before it settles down. The presence of foliage on the surface will help to speed up the process of preventing light getting to all the water.

If your pond has been filled for some time, then the algae growth is most probably due to the fact that you are topping up with fresh water owing to a leak. In this case, mend the leak and do not change the water once you have re-filled the pool.

My pool is overgrown with plants and weeds. What should I do with it?

The first thing is to decide which plants you want to keep, and remove some crowns of these to a temporary home (a water-filled liner laid over a low circle of bricks is ideal). Then scrap the remaining plants, (they make good compost) or give them away.

Save the animal life in the same way as you preserve the plants (with a water-filled liner)—but separately, providing them with some degree of shade as well.

Clean the pool thoroughly, check for any leaks by filling it up without plants in it, and replace any damaged containers; renew the soil. Re-stock the pool first with the plants, then with the animals; make sure that the water temperature is the same all the time, otherwise you will risk losing the fish.

How often should I change my pool water? I have no pump to circulate it.

Never—unless you have to: the more often the water is changed, the greater the difficulty of maintaining the balance of life in the pool. Apart from replanting every 5 to 10 years, leave the pool to its own devices.

Although in an open site, my pool collects many leaves in autumn from my neighbour’s trees. Any advice?

Leaves rotting in a pool build up toxic gas, so they must be removed. The easiest solution is to place a net over the surface of the pond when the leaves begin to fall: it will save you a lot of work and will be there only for a short period. Clear the net periodically to admit light to the pond.

When is the best time to clear a pond of rotting and dead foliage?

In early spring from February to March, just as growth is starting; but do not do it during frosty weather. Handle the fish with care and remove them to water of the same temperature as that from which they have come.

How long can I keep a pool from the time of stocking it to the time of renewal?

So much depends on the initial stocking and subsequent maintenance that no hard-and-fast rules apply: it could be 3 or 30 years—though the latter is unlikely for a small pond. An average would be 8 to 10 years.

How can I prevent my pool from freezing over the entire surface (I have fish in it)?

The simplest way is to use a weighted plastic bottle, at least 300 mm (1 ft) long, floating so that the rim is about 150 mm (6 in) above the surface. Pour hot water into the bottle to thaw the ice surrounding it, then remove and refill it with a little warm water to thaw out thin ice when replacing it later the same day. This procedure is necessary only if the water has been frozen for more than 24 hours. Do not on any account attempt to crack the ice by hitting it: the shock of pressure would severely injure the fish.

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