Designing a raised pond for a small patio

A raised pond earns its place on a small patio

A raised pond is the most forgiving way to bring water into a courtyard, balcony or pocket-sized garden. There is no digging, no barrowing out of spoil, and no bending double to see what is happening under the surface. Because the water sits at waist height, you can feed, deadhead and net out leaves without kneeling on wet paving. Children are kept back from the edge, and awkward changes in level across a patio simply disappear behind the timber frame.

For a small patio, aim for a finished rim height of about 450–600mm. That is comfortable to sit on with a mug of tea, deep enough to give the water some thermal stability, and shallow enough to reach the bottom with your arm. A footprint of roughly 1.2m by 0.6m gives around 500–700 litres once the wall thickness and planting ledges are taken into account, which is a genuinely workable volume for a few plants and perhaps a small group of fish.

Choosing the site and getting the size right

Position matters more than the design of the box itself. Most flowering water plants, and water lilies in particular, want five or six hours of direct sun a day to perform well. Shelter from the prevailing wind keeps leaves intact and reduces evaporation, but full shade encourages algae and sulking plants.

• Keep it away from overhanging branches. Falling leaves foul the water, and falling blossom is worse.
• Check for a nearby outdoor socket if you plan a small pump or fountain, and remember that any electrical work outdoors must be done safely and protected by the appropriate device.
• Leave 600mm of clear space on at least one side for sitting, feeding and planting up.
• Avoid the route between the back door and the shed, and check the swing of gates and bin lids.

Build on something solid. Paving slabs laid level, or a strip of compacted hardcore topped with a thin concrete bed, will stop the frame settling and twisting once it is full of water. Water weighs one kilogram per litre, so a 700-litres pond is carrying the best part of a tonne.

Building a sturdy timber frame

New softwood sleepers of 100mm by 100mm, or 150mm by 150mm, are ideal. Buy timber that has been pressure-treated rather than creosoted; old-fashioned creosote is unpleasant for plants, fish and you. Lay the first course on a bed of damp mortar or on a strip of butyl rubber to keep damp away from the wood, then build up in overlapping courses like a giant log cabin, so each layer is staggered from the one below.

Fix each course with galvanised coach bolts or long stainless screws, two per corner, driven through pilot holes. Check for level at every stage. A frame that is 20mm out will show plainly once the water is in. Cap the top course with a flat board wide enough to sit on, overhanging the inside by about 50mm; this gives you a ledge to tuck the liner into and hides the untidy edge of the water.

Liner, underlay and filling

Butyl or EPDM rubber liner will outlast most garden projects, and the thicker grades are worth the extra. Line the inside of the frame with a geotextile underlay, taking it over the top of the capping board, then lay the liner on top. Ease it into the corners rather than forcing it, and allow plenty of slack; liners stretch as the water goes in.

Fill with a hose, then let the pond stand for a couple of days before planting. Tap water is fine, but if you are stocking promptly, use a dechlorinator or top up from a water butt. Add an overflow point at the top of the liner for heavy rain, and a gently sloping ramp of stone or roughened timber so hedgehogs, frogs and beetles can climb out and do not drown.

Planting a small pond well

Limited volume means every plant must justify its space. Use aquatic baskets filled with a heavy loam-based compost, topped with gravel, and stand them on an internal shelf of blocks set at 200mm depth.

• Marginals: brooklime, water forget-me-not, dwarf iris, marsh marigold, water mint in a basket.
• Oxygenators: hornwort or water starwort, which keep the water clear and give wildlife cover.
• Floaters and lilies: a pygmy water lily for colour, or water soldier, which sinks in winter.

Keep fish numbers low. A pond of this size suits a handful of small goldfish or none at all; a plant-and-wildlife pond needs far less intervention and rarely goes green. Herons are persistent visitors to even the smallest patio, so either build the rim high and steep, or be ready with netting.

Routine care through the year

Little and often is the rule. Net out fallen leaves in autumn and remove yellowing foliage, twisting out blanketweed rather than reaching for chemicals. Top up with rainwater where possible, and check the timber for soft patches each spring, treating the outside with a water-based preservative when the pond is well covered. Feed fish only in warm weather, when they are actively swimming. In winter, never smash ice, which can stun fish; float a rubber ball or leave a small area open. Come April, divide congested baskets and you will keep a small patio pond looking generous for years.